顔写真

オオガネ ミキヒコ
大兼 幹彦
Mikihiko Ogane
所属
大学院工学研究科 応用物理学専攻 応用界面物理学講座(スピンエレクトロニクス分野)
職名
教授
学位
  • 博士(工学)(東北大学)

  • 修士(工学)(東北大学)

委員歴 6

  • 電気学会 調査専門委員会委員

    2019年4月 ~ 継続中

  • 日本磁気学会 企画委員

    2018年4月 ~ 継続中

  • 応用物理学会 スピントロニクス研究会幹事

    2009年4月 ~ 継続中

  • 日本磁気学会 編集・論文委員

    2014年12月 ~ 2017年5月

  • 応用物理学会 代議員

    2013年1月 ~ 2017年1月

  • 応用物理学会・スピントロニクス研究会 庶務会計幹事

    2011年1月 ~ 2012年12月

︎全件表示 ︎最初の5件までを表示

所属学協会 4

  • 一般社団法人 電気学会

    2023年4月 ~ 継続中

  • 日本生体磁気学会

    2022年6月 ~

  • 応用物理学会

  • 日本磁気学会

研究キーワード 5

  • 量子磁気センサ

  • 磁性薄膜

  • トンネル接合

  • MRAM

  • スピンエレクトロニクス

研究分野 2

  • ナノテク・材料 / ナノバイオサイエンス /

  • ナノテク・材料 / ナノ材料科学 /

受賞 12

  1. 研究奨励賞

    2022年5月 みやぎ産業科学振興基金 量子スピントロニクスセンサの 超高感度化に関する研究

  2. Applied Physics Express 2021 Spotlight

    2021年11月 応用物理学会

  3. 第6回青葉工学振興会賞

    2012年12月7日 (財)青葉工学振興会

  4. 第22回トーキン科学技術振興財団研究奨励賞

    2012年3月 第22回トーキン科学技術振興財団研究奨励賞

  5. 第44回応用物理学会優秀論文賞

    2023年3月 応用物理学会

  6. JPSJ Papers of Editor’s Choice

    2021年6月 日本物理学会

  7. 支部貢献賞

    2018年12月 応用物理学会

  8. 第39回日本磁気学会論文賞

    2015年9月 日本磁気学会

  9. 第34回応用物理学会優秀論文賞

    2012年9月11日 応用物理学会

  10. 日本磁気学会論文賞

    2008年9月 日本磁気学会

  11. 日本応用磁気学会学術奨励賞

    2007年8月 日本応用磁気学会

  12. Young Researcher Award ISAM2-2003

    2003年10月8日 日本MRS

︎全件表示 ︎最初の5件までを表示

論文 289

  1. Enhanced sensitivity and thermal tolerance in tunnel magnetoresistance sensor using Ta-doped CoFeSiB soft magnetic layer

    Takafumi Nakano, Kosuke Fujiwara, Masakiyo Tsunoda, Seiji Kumagai, Mikihiko Oogane

    Applied Physics Letters 123 (7) 2023年8月14日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0162276  

    ISSN:0003-6951

    eISSN:1077-3118

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    We developed a tunnel magnetoresistance (TMR) sensor consisting of a CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) and a CoFeSiB amorphous soft magnetic layer. This multilayer structure is promising for a high-sensitivity sensor because a giant TMR ratio of the MTJ and a small anisotropy field Hk of the free layer can be obtained simultaneously. However, the soft magnetic properties of the CoFeSiB layer disappear when it is annealed at above the crystallization temperature (around 300 °C), which determines the thermal tolerance of the TMR sensor and limits improvements to the sensor's sensitivity and applications. In this study, we doped the CoFeSiB layer with various amounts of Ta to raise its crystallization temperature. TMR sensors using the Ta-doped CoFeSiB layers showed thermal tolerance to annealing temperatures above 425 °C, whereas the sensor with the undoped CoFeSiB layer was tolerant to annealing temperatures up to 325 °C. As well, the Ta doping effectively reduced Hk of the CoFeSiB layer, which resulted in a sensitivity of 50%/Oe, over three times higher than the sensor with the undoped CoFeSiB layer. These results pave the way toward next-generation TMR sensors having higher sensitivity and wider applicability.

  2. Prediction of Magnetocrystalline Anisotropy Constant in FeCoNi Alloys Using Machine Learning

    Ren Sudo, Mikihiko Oogane

    2023 IEEE International Magnetic Conference - Short Papers (INTERMAG Short Papers) 2023年5月

    出版者・発行元:IEEE

    DOI: 10.1109/intermagshortpapers58606.2023.10228569  

  3. TaFeB spacer for soft magnetic composite free layer in CoFeB/MgO/CoFeB-based magnetic tunnel junction 査読有り

    Takafumi Nakano, Kosuke Fujiwara, Seiji Kumagai, Yasuo Ando, Mikihiko Oogane

    Applied Physics Letters 122 (7) 072405 2023年2月13日

    DOI: 10.1063/5.0132866  

  4. Tunnel anisotropic magnetoresistance in magnetic tunnel junctions using FeAlSi 査読有り

    S. Akamatsu, T. Nakano, Muftah Al-Mahdawi, W. Yupeng, M. Tsunoda, Y. Ando, M. Oogane

    AIP Advances 13 (2) 025005 2023年2月1日

    DOI: 10.1063/9.0000440  

  5. Low magnetic damping constant in half-metallic Co2FeAl Heusler alloy thin films grown by molecular beam epitaxy 査読有り

    Takayuki Hojo, Nobuki Tezuka, Takafumi Nakano, Masakiyo Tsunoda, Mikihiko Oogane

    AIP Advances 13 (2) 025204 2023年2月1日

    DOI: 10.1063/9.0000419  

  6. Development of Magnetocardiograph without Magnetically Shielded Room Using High-Detectivity TMR Sensors

    Koshi Kurashima, Makoto Kataoka, Takafumi Nakano, Kosuke Fujiwara, Seiichi Kato, Takenobu Nakamura, Masaki Yuzawa, Masanori Masuda, Kakeru Ichimura, Shigeki Okatake, Yoshitaka Moriyasu, Kazuhiro Sugiyama, Mikihiko Oogane, Yasuo Ando, Seiji Kumagai, Hitoshi Matsuzaki, Hidenori Mochizuki

    Sensors 23 (2) 646-646 2023年1月6日

    出版者・発行元:MDPI AG

    DOI: 10.3390/s23020646  

    eISSN:1424-8220

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    A magnetocardiograph that enables the clear observation of heart magnetic field mappings without magnetically shielded rooms at room temperatures has been successfully manufactured. Compared to widespread electrocardiographs, magnetocardiographs commonly have a higher spatial resolution, which is expected to lead to early diagnoses of ischemic heart disease and high diagnostic accuracy of ventricular arrhythmia, which involves the risk of sudden death. However, as the conventional superconducting quantum interference device (SQUID) magnetocardiographs require large magnetically shielded rooms and huge running costs to cool the SQUID sensors, magnetocardiography is still unfamiliar technology. Here, in order to achieve the heart field detectivity of 1.0 pT without magnetically shielded rooms and enough magnetocardiography accuracy, we aimed to improve the detectivity of tunneling magnetoresistance (TMR) sensors and to decrease the environmental and sensor noises with a mathematical algorithm. The magnetic detectivity of the TMR sensors was confirmed to be 14.1 pTrms on average in the frequency band between 0.2 and 100 Hz in uncooled states, thanks to the original multilayer structure and the innovative pattern of free layers. By constructing a sensor array using 288 TMR sensors and applying the mathematical magnetic shield technology of signal space separation (SSS), we confirmed that SSS reduces the environmental magnetic noise by −73 dB, which overtakes the general triple magnetically shielded rooms. Moreover, applying digital processing that combined the signal average of heart magnetic fields for one minute and the projection operation, we succeeded in reducing the sensor noise by about −23 dB. The heart magnetic field resolution measured on a subject in a laboratory in an office building was 0.99 pTrms and obtained magnetocardiograms and current arrow maps as clear as the SQUID magnetocardiograph does in the QRS and ST segments. Upon utilizing its superior spatial resolution, this magnetocardiograph has the potential to be an important tool for the early diagnosis of ischemic heart disease and the risk management of sudden death triggered by ventricular arrhythmia.

  7. Magnetic Hammer Testing with Tunnel Magnetoresistive Sensors

    Jun Ito, Muftah Al-Mahdawi, Mikihiko Oogane

    IEEE Transactions on Magnetics 1-1 2023年

    出版者・発行元:Institute of Electrical and Electronics Engineers (IEEE)

    DOI: 10.1109/tmag.2023.3282988  

    ISSN:0018-9464

    eISSN:1941-0069

  8. Ac Susceptibility Measurement Using a Vibrating Sample Magnetometer

    Muftah Al-Mahdawi, Mikihiko Oogane

    IEEE Transactions on Magnetics 1-1 2023年

    出版者・発行元:Institute of Electrical and Electronics Engineers (IEEE)

    DOI: 10.1109/tmag.2023.3300268  

    ISSN:0018-9464

    eISSN:1941-0069

  9. Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

    Akitake Kanno, Nobukazu Nakasato, Mikihiko Oogane, Kosuke Fujiwara, Takafumi Nakano, Tadashi Arimoto, Hitoshi Matsuzaki, Yasuo Ando

    Scientific Reports 12 (1) 2022年12月

    出版者・発行元:Springer Science and Business Media LLC

    DOI: 10.1038/s41598-022-10155-6  

    eISSN:2045-2322

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    Abstract Non-invasive human brain functional imaging with millisecond resolution can be achieved only with magnetoencephalography (MEG) and electroencephalography (EEG). MEG has better spatial resolution than EEG because signal distortion due to inhomogeneous head conductivity is negligible in MEG but serious in EEG. However, this advantage has been practically limited by the necessary setback distances between the sensors and scalp, because the Dewar vessel containing liquid helium for superconducting quantum interference devices (SQUIDs) requires a thick vacuum wall. Latest developments of high critical temperature (high-T<sub>c</sub>) SQUIDs or optically pumped magnetometers have allowed closer placement of MEG sensors to the scalp. Here we introduce the use of tunnel magneto-resistive (TMR) sensors for scalp-attached MEG. Improvement of TMR sensitivity with magnetic flux concentrators enabled scalp-tangential MEG at 2.6 mm above the scalp, to target the largest signal component produced by the neural current below. In a healthy subject, our single-channel TMR-MEG system clearly demonstrated the N20m, the initial cortical component of the somatosensory evoked response after median nerve stimulation. Multisite measurement confirmed a spatially and temporally steep peak of N20m, immediately above the source at a latency around 20 ms, indicating a new approach to non-invasive functional brain imaging with millimeter and millisecond resolutions.

  10. Magnetic tunnel junctions using epitaxially grown FeAlSi electrode with soft magnetic property 査読有り

    Shoma Akamatsu, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

    AIP Advances 12 (7) 075021-075021 2022年7月1日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0094619  

    eISSN:2158-3226

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    Magnetic tunnel junctions (MTJs) with (001)-oriented D0<sub>3</sub>-FeAlSi epitaxial films, which have both soft magnetic properties and surface flatness, were fabricated and characterized. A tunnel magnetoresistance (TMR) ratio of 121% was observed, and a relatively low switching field was also confirmed, reflecting the soft magnetic property of FeAlSi. However, the results of the cross-sectional TEM image of the MTJ and the bias dependence of the TMR ratio indicate that the FeAlSi/MgO interface is probably oxidized. Therefore, since an insertion layer at the interface can suppress oxidation and further improve the TMR ratio, MTJs using FeAlSi epitaxial films are promising structures suitable for applications such as MTJ-based magnetic sensors and worthy of further investigation.

  11. Guidelines for attaining optimal soft magnetic properties in FeAlSi films 査読有り

    Shoma Akamatsu, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

    Applied Physics Letters 120 (24) 242406-242406 2022年6月13日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0086322  

    ISSN:0003-6951

    eISSN:1077-3118

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    Nm-order FeAlSi epitaxial films with a partially D0<sub>3</sub>-ordered structure were grown on MgO substrates, and ideal soft magnetic properties were obtained. We found that the sign of the magnetocrystalline anisotropy constant K<sub>1</sub> changes with increasing annealing temperature for certain FeAlSi compositions. This is caused by a change in the volume balance of the ordered phases with the annealing process and the point at which K<sub>1</sub> ∼ 0 shifts to the Al-rich concentration as the degree of D0<sub>3</sub>-ordering decreases. K<sub>1</sub> was precisely measured by ferromagnetic resonance under the optimal condition, and the value of 1.6 × 10<sup>2</sup> (erg/cc) was obtained, which is comparable to that of bulk. The uniaxial component of the magnetic anisotropy due to magnetostriction was small, and a fourfold symmetric component due to magnetocrystalline anisotropy was dominant.

  12. Control of sensitivity in vortex-type magnetic tunnel junction magnetometer sensors by the pinned layer geometry 査読有り

    Motoki Endo, Muftah Al-Mahdawi, Mikihiko Oogane, Yasuo Ando

    Journal of Physics D: Applied Physics 55 (19) 195001-195001 2022年5月12日

    出版者・発行元:IOP Publishing

    DOI: 10.1088/1361-6463/ac5080  

    ISSN:0022-3727

    eISSN:1361-6463

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    Abstract The tuning of sensitivity and dynamic range in linear magnetic sensors is required in various applications. We demonstrate the control and design of the sensitivity in magnetic tunnel junction (MTJ) sensors with a vortex-type sensing layer. In this work, we develop sensor MTJs with NiFe sensing layers having a vortex magnetic configuration. We demonstrate that by varying the pinned layer size, the sensitivity to magnetic field is tuned linearly. We obtain a high magnetoresistance ratio of 140%, and we demonstrate a controllable sensitivity from 0.85% Oe<sup>−1</sup> to 4.43% Oe<sup>−1</sup>, while keeping the vortex layer fixed in size. We compare our experimental results with micromagnetic simulations. We find that the linear displacement of vortex core by an applied field makes the design of vortex sensors simple. The control of the pinned layer geometry is an effective method to increase the sensitivity, without affecting the vortex state of the sensing layer. Furthermore, we propose that the location of the pinned layer can be used to realize more sensing functionalities from a single sensor.

  13. Observation of unconventional spin-polarization induced spin–orbit torque in L1<sub>2</sub>-ordered antiferromagnetic Mn<sub>3</sub>Pt thin films 査読有り

    Longjie Yu, Shutaro Karube, Min Liu, Masakiyo Tsunoda, Mikihiko Oogane, Yasuo Ando

    Applied Physics Express 15 (3) 033002-033002 2022年3月1日

    出版者・発行元:IOP Publishing

    DOI: 10.35848/1882-0786/ac52d7  

    ISSN:1882-0778

    eISSN:1882-0786

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    Abstract Non-collinear antiferromagnets exhibit richer magneto-transport properties compared to nonmagnetic materials due to the topological spin structure they possess, which allows us to manipulate the charge-spin conversion more freely by taking advantage of the chirality. In this work, we explore the unconventional spin–orbit torque of L1<sub>2</sub>-ordered Mn<sub>3</sub>Pt with a triangular spin structure. We observed an unconventional spin–orbit torque along the x-direction for the (001)-oriented L1<sub>2</sub> Mn<sub>3</sub>Pt and found that it has a sign reversal behavior relative to the crystalline orientation. This generation of unconventional spin–orbit torque can be interpreted as stemming from the magnetic spin Hall effect.

  14. 最新のセンサー系から見た心臓磁場計測技術と脳磁場計測に向けた展望 室温動作TMRセンサーを用いたリアルタイム心磁場および体性感覚誘発脳磁場の計測

    藤原 耕輔, 菅野 彰剛, 中野 貴文, 熊谷 静似, 松崎 斉, 有本 直, 大兼 幹彦, 中里 信和, 安藤 康夫

    日本生体磁気学会誌 35 (1) 76-77 2022年

    出版者・発行元:日本生体磁気学会

    ISSN:0915-0374

  15. Deep Learning Models for Magnetic Cardiography Edge Sensors Implementing Noise Processing and Diagnostics 査読有り

    Sadman Sakib, Mostafa M. Fouda, Muftah Al-Mahdawi, Attayeb Mohsen, Mikihiko Oogane, Yasuo Ando, Zubair Md. Fadlullah

    IEEE Access 10 2656-2668 2022年

    出版者・発行元:Institute of Electrical and Electronics Engineers (IEEE)

    DOI: 10.1109/access.2021.3138976  

    eISSN:2169-3536

  16. Sub-pT magnetic field detection by tunnel magneto-resistive sensors

    Mikihiko Oogane, Kosuke Fujiwara, Akitake Kanno, Takafumi Nakano, Hiroshi Wagatsuma, Tadashi Arimoto, Shigemi Mizukami, Seiji Kumagai, Hitoshi Matsuzaki, Nobukazu Nakasato, Yasuo Ando

    Applied Physics Express 14 (12) 123002-123002 2021年12月1日

    出版者・発行元:IOP Publishing

    DOI: 10.35848/1882-0786/ac3809  

    ISSN:1882-0778

    eISSN:1882-0786

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    <title>Abstract</title> We developed tunnel magneto-resistive (TMR) sensors based on magnetic tunnel junctions (MTJs) that are able to detect a weak, sub-pT, magnetic field at a low frequency. Small detectivities of 0.94 pT/Hz<sup>1/2</sup> at 1 Hz and 0.05 pT/Hz<sup>1/2</sup> at 1 kHz were achieved by lowering the resistance of MTJs and enhancement of the signal using a thick CoFeSiB layer and magnetic flux concentrators. We demonstrated real-time measurement of magnetocardiography (MCG) and nuclear magnetic resonance (NMR) of protons using developed sensors. This result shows that both MCG and NMR can be measured by the same measurement system with ultra-sensitive TMR sensors.

  17. 室温生体磁気計測の進歩:SQUIDを超えて TMRセンサの原理と心磁図計測

    大兼 幹彦, 菅野 彰剛, 藤原 耕輔, 中野 貴文, 熊谷 静似, 松崎 斉, 中里 信和, 安藤 康夫

    臨床神経生理学 49 (5) 299-299 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  18. 室温生体磁気計測の進歩:SQUIDを超えて 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 柿坂 庸介, 松崎 斉, 安藤 康夫, 中里 信和

    臨床神経生理学 49 (5) 300-300 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  19. 第32回小児脳機能研究会:臨床神経生理からみた小児の機能評価-中枢から末梢まで- 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 柿坂 庸介, 松崎 斉, 安藤 康夫, 中里 信和

    臨床神経生理学 49 (5) 371-371 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  20. 室温生体磁気計測の進歩:SQUIDを超えて TMRセンサの原理と心磁図計測

    大兼 幹彦, 菅野 彰剛, 藤原 耕輔, 中野 貴文, 熊谷 静似, 松崎 斉, 中里 信和, 安藤 康夫

    臨床神経生理学 49 (5) 299-299 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  21. 室温生体磁気計測の進歩:SQUIDを超えて 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 柿坂 庸介, 松崎 斉, 安藤 康夫, 中里 信和

    臨床神経生理学 49 (5) 300-300 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  22. 第32回小児脳機能研究会:臨床神経生理からみた小児の機能評価-中枢から末梢まで- 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 柿坂 庸介, 松崎 斉, 安藤 康夫, 中里 信和

    臨床神経生理学 49 (5) 371-371 2021年10月

    出版者・発行元:(一社)日本臨床神経生理学会

    ISSN:1345-7101

    eISSN:2188-031X

  23. Quadratic magnetoelectric effect during field cooling in sputter grown Cr2O3 films

    Muftah Al-Mahdawi, Tomohiro Nozaki, Mikihiko Oogane, Hiroshi Imamura, Yasuo Ando, Masashi Sahashi

    Physical Review Materials 5 (9) 2021年9月14日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevmaterials.5.094406  

    eISSN:2475-9953

  24. Brownian Motion of Magnetic Skyrmions in One- and Two-Dimensional Systems 査読有り

    Soma Miki, Yuma Jibiki, Eiiti Tamura, Minori Goto, Mikihiko Oogane, Jaehun Cho, Ryo Ishikawa, Hikaru Nomura, Yoshishige Suzuki

    Journal of the Physical Society of Japan 90 (8) 083601-083601 2021年8月15日

    出版者・発行元:Physical Society of Japan

    DOI: 10.7566/jpsj.90.083601  

    ISSN:0031-9015

    eISSN:1347-4073

  25. Noise-Removal from Spectrally-Similar Signals Using Reservoir Computing for MCG Monitoring

    Sadman Sakib, Mostafa M. Fouda, Muftah Al-Mahdawi, Attayeb Mohsen, Mikihiko Oogane, Yasuo Ando, Zubair Md Fadlullah

    ICC 2021 - IEEE International Conference on Communications 2021年6月

    出版者・発行元:IEEE

    DOI: 10.1109/icc42927.2021.9500993  

  26. Serial MTJ-Based TMR Sensors in Bridge Configuration for Detection of Fractured Steel Bar in Magnetic Flux Leakage Testing

    Zhenhu Jin, Muhamad Arif Ihsan Mohd Noor Sam, Mikihiko Oogane, Yasuo Ando

    Sensors 21 (2) 668-668 2021年1月19日

    出版者・発行元:MDPI AG

    DOI: 10.3390/s21020668  

    eISSN:1424-8220

    詳細を見る 詳細を閉じる

    Thanks to high sensitivity, excellent scalability, and low power consumption, magnetic tunnel junction (MTJ)-based tunnel magnetoresistance (TMR) sensors have been widely implemented in various industrial fields. In nondestructive magnetic flux leakage testing, the magnetic sensor plays a significant role in the detection results. As highly sensitive sensors, integrated MTJs can suppress frequency-dependent noise and thereby decrease detectivity; therefore, serial MTJ-based sensors allow for the design of high-performance sensors to measure variations in magnetic fields. In the present work, we fabricated serial MTJ-based TMR sensors and connected them to a full Wheatstone bridge circuit. Because noise power can be suppressed by using bridge configuration, the TMR sensor with Wheatstone bridge configuration showed low noise spectral density (0.19 μV/Hz0.5) and excellent detectivity (5.29 × 10−8 Oe/Hz0.5) at a frequency of 1 Hz. Furthermore, in magnetic flux leakage testing, compared with one TMR sensor, the Wheatstone bridge TMR sensors provided a higher signal-to-noise ratio for inspection of a steel bar. The one TMR sensor system could provide a high defect signal due to its high sensitivity at low lift-off (4 cm). However, as a result of its excellent detectivity, the full Wheatstone bridge-based TMR sensor detected the defect even at high lift-off (20 cm). This suggests that the developed TMR sensor provides excellent detectivity, detecting weak field changes in magnetic flux leakage testing.

  27. トンネル磁気抵抗素子を用いた室温脳磁計による体性感覚誘発磁界の測定

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 松﨑 斉, 安藤 康夫, 中里 信和

    生体医工学 59 752-753 2021年

    出版者・発行元:公益社団法人 日本生体医工学会

    DOI: 10.11239/jsmbe.Annual59.752  

    ISSN:1347-443X

    詳細を見る 詳細を閉じる

    <p>"【背景】従来の脳磁計は超伝導量子干渉素子(SQUID)を液体ヘリウム容器に格納する必要があり、センサと頭皮との距離が離れる欠点があった。我々は室温で体表に接した生体磁気計測を可能とすべく、トンネル磁気抵抗(TMR)素子を用いたセンサを開発し、すでに健常被験者における心磁図や脳磁図アルファ波の計測に成功している。今回、正中神経刺激による体性感覚誘発磁界の第1波N20mを再現性よく計測できたので報告する。【方法】健常被験者の左手首の正中神経刺激を、通常の臨床検査と同様に、持続時間は0.3 ms、刺激頻度は2.9 Hz、刺激強度は母指外転筋運動閾値の1.5倍で刺激した。磁気シールド室内で、1チャンネルのTMR素子(JST S-イノベプロジェクトで製作)と磁束集束構造を組み合わせた磁気センサを、被験者の右頭頂部に固定し、頭皮に水平な磁界成分を計測した。得られた信号は16ビットでサンプル周波数2,000HzにてA/D変換し、帯域フィルタ5-250Hzで処理後に、波形が明瞭になるまで合計1,000から5,000回の平均加算を行った。【結果】刺激から潜時約20msに頂点をもつ第1波と、その後の第2、第3波が明瞭に記録され、同一被験者でSQUID脳磁計にて測定した波形と同一成分と確認できた。【結語】今回の結果は、TMR脳磁計の実用化に大きく寄与するものと期待される。"</p>

  28. トンネル磁気抵抗素子を用いた室温脳磁計による体性感覚誘発磁界の測定

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 松﨑 斉, 安藤 康夫, 中里 信和

    生体医工学 59 243-243 2021年

    出版者・発行元:公益社団法人 日本生体医工学会

    DOI: 10.11239/jsmbe.Annual59.243  

    ISSN:1347-443X

    詳細を見る 詳細を閉じる

    <p>【背景】従来の脳磁計は超伝導量子干渉素子(SQUID)を液体ヘリウム容器に格納する必要があり、センサと頭皮との距離が離れる欠点があった。我々は室温で体表に接した生体磁気計測を可能とすべく、トンネル磁気抵抗(TMR)素子を用いたセンサを開発し、すでに健常被験者における心磁図や脳磁図アルファ波の計測に成功している。今回、正中神経刺激による体性感覚誘発磁界の第1波N20mを再現性よく計測できたので報告する。【方法】健常被験者の左手首の正中神経刺激を、通常の臨床検査と同様に、持続時間は0.3 ms、刺激頻度は2.9 Hz、刺激強度は母指外転筋運動閾値の1.5倍で刺激した。磁気シールド室内で、1チャンネルのTMR素子(JST S-イノベプロジェクトで製作)と磁束集束構造を組み合わせた磁気センサを、被験者の右頭頂部に固定し、頭皮に水平な磁界成分を計測した。得られた信号は16ビットでサンプル周波数2,000HzにてA/D変換し、帯域フィルタ5-250Hzで処理後に、波形が明瞭になるまで合計1,000から5,000回の平均加算を行った。【結果】刺激から潜時約20msに頂点をもつ第1波と、その後の第2、第3波が明瞭に記録され、同一被験者でSQUID脳磁計にて測定した波形と同一成分と確認できた。【結語】今回の結果は、TMR脳磁計の実用化に大きく寄与するものと期待される。</p>

  29. トンネル磁気抵抗素子を用いた室温脳磁計による体性感覚誘発磁界の測定

    菅野 彰剛, 大兼 幹彦, 藤原 耕輔, 松崎 斉, 安藤 康夫, 中里 信和

    日本生体磁気学会誌 34 (1) 112-113 2021年

    出版者・発行元:日本生体磁気学会

    ISSN:0915-0374

  30. Highly-sensitive magnetic sensor for detecting magnetic nanoparticles based on magnetic tunnel junctions at a low static field

    Z. Jin, Thomas Myeongseok Koo, Myeong Soo Kim, M. Al-Mahdawi, M. Oogane, Y. Ando, Young Keun Kim

    AIP Advances 11 (1) 015046-015046 2021年1月1日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/9.0000189  

    eISSN:2158-3226

  31. Detection of Small Magnetic Fields Using Serial Magnetic Tunnel Junctions with Various Geometrical Characteristics

    Zhenhu Jin, Yupeng Wang, Kosuke Fujiwara, Mikihiko Oogane, Yasuo Ando

    Sensors 20 (19) 5704-5704 2020年10月7日

    出版者・発行元:MDPI AG

    DOI: 10.3390/s20195704  

    eISSN:1424-8220

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    Thanks to their high magnetoresistance and integration capability, magnetic tunnel junction-based magnetoresistive sensors are widely utilized to detect weak, low-frequency magnetic fields in a variety of applications. The low detectivity of MTJs is necessary to obtain a high signal-to-noise ratio when detecting small variations in magnetic fields. We fabricated serial MTJ-based sensors with various junction area and free-layer electrode aspect ratios. Our investigation showed that their sensitivity and noise power are affected by the MTJ geometry due to the variation in the magnetic shape anisotropy. Their MR curves demonstrated a decrease in sensitivity with an increase in the aspect ratio of the free-layer electrode, and their noise properties showed that MTJs with larger junction areas exhibit lower noise spectral density in the low-frequency region. All of the sensors were able detect a small AC magnetic field (Hrms = 0.3 Oe at 23 Hz). Among the MTJ sensors we examined, the sensor with a square-free layer and large junction area exhibited a high signal-to-noise ratio (4792 ± 646). These results suggest that MTJ geometrical characteristics play a critical role in enhancing the detectivity of MTJ-based sensors.

  32. AI Aided Noise Processing of Spintronic Based IoT Sensor for Magnetocardiography Application

    Attayeb Mohsen, Muftah Al-Mahdawi, Mostafa M. Fouda, Mikihiko Oogane, Yasuo Ando, Zubair Md Fadlullah

    ICC 2020 - 2020 IEEE International Conference on Communications (ICC) 2020年6月

    出版者・発行元:IEEE

    DOI: 10.1109/icc40277.2020.9148617  

  33. High-Temperature Magnetic Tunnel Junction Magnetometers Based on L1$_0$-PtMn Pinned Layer

    Sina Ranjbar, Muftah Al-Mahdawi, Mikihiko Oogane, Yasuo Ando

    IEEE Sensors Letters 4 (5) 1-4 2020年5月

    出版者・発行元:Institute of Electrical and Electronics Engineers (IEEE)

    DOI: 10.1109/lsens.2020.2991654  

    eISSN:2475-1472

  34. Controlling domain configuration of the sensing layer for magnetic tunneling junctions by using exchange bias

    Sina Ranjbar, Muftah Al-Mahdawi, Mikihiko Oogane, Yasuo Ando

    AIP Advances 10 (2) 025119-025119 2020年2月1日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/1.5130486  

    eISSN:2158-3226

  35. Large spin signals in n+ -Si/MgO/ Co2Fe0.4Mn0.6Si lateral spin-valve devices 査読有り

    T. Koike, M. Oogane, M. Tsunoda, Y. Ando

    127 (8) 085306-1-085306-8 2020年2月

  36. Fabrication and evaluation of highly c-plane oriented Mn3Sn thin films 査読有り

    T. Ikeda, M. Tsunoda, M. Oogane, S. Oh, T. Morita, Y. Ando

    AIP Advances 10 015310-1-015310-5 2020年1月

  37. Fabrication of soft-magnetic FeAlSi thin films with nm-order thickness for the free layer of magnetic tunnel junction based sensors 査読有り

    S. Akamatsu, M. Oogane, M. Tsunoda, Y. Ando

    AIP Advances 10 015302-1-015302-4 2020年1月

  38. Composition dependence of the secondorder interfacial magnetic anisotropy for MgO/CoFeB/Ta films 査読有り

    T. Ogasawara, M. Oogane, M. Al-Mahdawi, M. Tsunoda, Y. Ando

    AIP Advances 9 125053-1-125053-5 2019年12月

  39. Polycrystalline Co2Fe0.4Mn0.6Si Heusler alloy thin films with high B2 ordering and small magnetic anisotropy for magnetic tunnel junction based sensors 査読有り

    N. Kudo, M. Oogane, M. Tsunoda, Y. Ando

    AIP Advances 9 125036-1-125036-4 2019年12月

  40. Effect of second-order magnetic anisotropy on nonlinearity of conductance in CoFeB/MgO/CoFeB magnetic tunnel junction for magnetic sensor devices 査読有り

    T. Ogasawara, M. Oogane, M. Al-Mahdawi, M. Tsunoda, Y. Ando

    Scientific Reports 9 17018-1-17018-9 2019年11月

  41. Investigation of a Magnetic Tunnel Junction Based Sensor for the Detection of Defects in Reinforced Concrete at High Lift-Off

    Muhamad Arif Ihsan Mohd Noor Sam, Zhenhu Jin, Mikihiko Oogane, Yasuo Ando

    Sensors 19 (21) 4718-4718 2019年10月30日

    出版者・発行元:MDPI AG

    DOI: 10.3390/s19214718  

    eISSN:1424-8220

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    Magnetic flux leakage (MFL) testing is a method of non-destructive testing (NDT), whereby the material is magnetized, and when a defect is present, the magnetic flux lines break out of the material. The magnitude of the leaked magnetic flux decreases as the lift-off (distance from the material) increases. Therefore, for detection at high lift-off, a sensitive magnetic sensor is required. To increase the output sensitivity, this paper proposes the application of magnetic tunnel junction (MTJ) sensors in a bridge circuit for the NDT of reinforced concrete at high lift-off. MTJ sensors were connected to a full-bridge circuit, where one side of the arm has two MTJ sensors connected in series, and the other contains a resistor and a variable resistor. Their responses towards a bias magnetic field were measured, and, based on the results, the sensor circuit sensitivity was 0.135 mV/mT. Finally, a reinforced concrete specimen with a 1 cm gap in the center was detected. The sensor module (with an amplifier and low pass filter circuits) could determine the gap even at 50 cm, suggesting that MTJ sensors have the potential to detect defects at high lift-off values and have a promising future in the field of NDT.

  42. Composition dependence of exchange anisotropy in PtxMn100−x/CoyFe100-y films 査読有り

    S. Ranjbar, M. Tsunoda, M. Al-Mahdawi, M. Oogane, Y. Ando

    IEEE Magnetics Letters 10 4505905-1-4505905-5 2019年10月

  43. 高感度・高信頼性TMR磁気センサの開発 招待有り 査読有り

    大兼 幹彦, 中野 貴文

    まぐね 14 (5) 260-267 2019年10月

  44. Improvement of Large Anomalous Hall Effect in Polycrystalline Antiferromagnetic Mn3+xSn Thin Films 査読有り

    Ikeda Tomoki, Tsunoda Masakiyo, Oogane Mikihiko, Oh Seungjun, Morita Tadashi, Ando Yasuo

    IEEE TRANSACTIONS ON MAGNETICS 55 (7) 2019年7月

    DOI: 10.1109/TMAG.2019.2899223  

    ISSN:0018-9464

  45. Controlled growth and magnetic property of a-plane-oriented Mn3Sn thin films 査読有り

    Oh Seungjun, Morita Tadashi, Ikeda Tomoki, Tsunoda Masakiyo, Oogane Mikihiko, Ando Yasuo

    AIP ADVANCES 9 (3) 2019年3月

    DOI: 10.1063/1.5079688  

    ISSN:2158-3226

  46. Serial magnetic tunnel junction based sensors for detecting far-side pitsin metallic specimens 査読有り

    Zhenhu Jin, Muhamad Arif Ihsan, Mikihiko Oogane, Kousuke Fujiwara, Yasuo Ando

    Japanese Journal of Applied Physics 58 043003-1-043003-6 2019年3月

    DOI: 10.7567/1347-4065/aafe71  

  47. Composition dependence of exchange anisotropy in PtxMn1−x/Co70Fe30 films 査読有り

    Sina Ranjbar, Masakiyo Tsunoda, Mikihiko Oogane, Yasuo Ando

    Japanese Journal of Applied Physics 58 043001-1-043001-5 2019年3月

    DOI: 10.7567/1347-4065/ab03e3  

  48. Epitaxial L10-MnAl Thin Films With High Perpendicular Magnetic Anisotropy and Small Surface Roughness 査読有り

    Most Shahnaz Parvin, Mikihiko Oogane, Miho Kubota, Masakiyo Tsunoda, Yasuo Ando

    EEE TRANSACTIONS ON MAGNETICS 54 (11) 3401704-1-3401704-4 2018年11月

    DOI: 10.1109/TMAG.2018.2834553  

    ISSN:0018-9464

  49. Anomalous Hall effect in polycrystalline Mn3Sn thin films 査読有り

    Tomoki Ikeda, Masakiyo Tsunoda, Mikihiko Oogane, Seungjun Oh, Tadashi Morita, Yasuo Ando

    APPLIED PHYSICS LETTERS 113 222405-1-222405-5 2018年11月

    DOI: 10.1063/1.5051495  

  50. Effects of annealing temperature on sensing properties of magnetic-tunnel-junction-based sensors with perpendicular syntheticantiferromagnetic Co/Pt pinned layer 査読有り

    Takahiro Ogasawara, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

    Japanese Journal of AppliedPhysics 57 (11) 110308-1-110308-4 2018年10月

    DOI: 10.7567/JJAP.57.110308  

  51. Large exchange coupling field in perpendicular synthetic antiferromagnetic structures with CoPt alloy 査読有り

    Takahiro Ogasawara, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

    Japanese Journal of Applied Physics 57 088004 2018年7月

  52. Annealing effect on interlayer exchange coupling in perpendicularly magnetized synthetic antiferromagnetic structure based on Co/Pd multilayers with ultrathin Ru spacer 査読有り

    Takafumi Nakano, Mikihiko Oogane, Yasuo Ando

    Japanese Journal of Applied Physics 57 073001 2018年6月

  53. Low magnetic damping and large negative anisotropic magnetoresistance in half-metallic Co2-xMn1+xSi Heusler alloy films grown by molecular beam epitaxy 査読有り

    Mikihiko Oogane, Anthony P. McFadden, Kenji Fukuda, Masakiyo Tsunoda, Yasuo Ando, Chris J. Palmstrom

    APPLIED PHYSICS LETTERS 112 262407 2018年6月

  54. Fourfold symmetric anisotropic magnetoresistance in half-metallic Co2MnSi Heusler alloy thin films 査読有り

    Mikihiko Oogane, Anthony P. McFadden, Yohei Kota, Tobias L. Brown-Heft, Masakiyo Tsunoda, Yasuo Ando, Chris J. Palmstrom

    Japanese Journal of Applied Physics 57 063001 2018年4月

  55. Magnetic-sensor performance evaluated from magneto-conductance curve in magnetic tunnel junctions using in-plane or perpendicularly magnetized synthetic antiferromagnetic reference layers 査読有り

    T. Nakano, M. Oogane, T. Furuichi, Y. Ando

    AIP Advances 8 (4) 045011 2018年4月1日

    出版者・発行元:American Institute of Physics Inc.

    DOI: 10.1063/1.5027768  

    ISSN:2158-3226

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    The automotive industry requires magnetic sensors exhibiting highly linear output within a dynamic range as wide as ±1 kOe. A simple model predicts that the magneto-conductance (G-H) curve in a magnetic tunnel junction (MTJ) is perfectly linear, whereas the magneto-resistance (R-H) curve inevitably contains a finite nonlinearity. We prepared two kinds of MTJs using in-plane or perpendicularly magnetized synthetic antiferromagnetic (i-SAF or p-SAF) reference layers and investigated their sensor performance. In the MTJ with the i-SAF reference layer, the G-H curve did not necessarily show smaller nonlinearities than those of the R-H curve with different dynamic ranges. This is because the magnetizations of the i-SAF reference layer start to rotate at a magnetic field even smaller than the switching field (Hsw) measured by a magnetometer, which significantly affects the tunnel magnetoresistance (TMR) effect. In the MTJ with the p-SAF reference layer, the G-H curve showed much smaller nonlinearities than those of the R-H curve, thanks to a large Hsw value of the p-SAF reference layer. We achieved a nonlinearity of 0.08% FS (full scale) in the G-H curve with a dynamic range of ±1 kOe, satisfying our target for automotive applications. This demonstrated that a reference layer exhibiting a large Hsw value is indispensable in order to achieve a highly linear G-H curve.

  56. Realization of a Spin-Wave Switch Based on the Spin-Transfer-Torque Effect 査読有り

    Thomas Meyer, Thomas Br ̈ acher, Frank Heussner, Alexander A. Serga, Hiroshi Naganuma, Koki Mukaiyama, Mikihiko Oogane, Yasuo Ando, Burkard Hillebrands, d Philipp Pirro

    IEEE MAGNETICS LETTERS 9 3102005-1-3102005-5 2018年2月

    DOI: 10.1109/LMAG.2018.2803737  

  57. Characterization of spin-transfer-torque effect induced magnetization dynamics driven by short current pulses 査読有り

    T. Meyer, T. Brächer, F. Heussner, A. A. Serga, H. Naganuma, K. Mukaiyama, M. Oogane, Y. Ando, B. Hillebrands, P. Pirro

    Applied Physics Letters 112 (2) 022401 2018年1月8日

    出版者・発行元:American Institute of Physics Inc.

    DOI: 10.1063/1.5011721  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We present a time-resolved study of the magnetization dynamics in a microstructured Cr|Heusler|Pt waveguide driven by the spin-Hall-effect and the spin-transfer-torque effect via short current pulses. In particular, we focus on the determination of the threshold current at which the spin-wave damping is compensated. We have developed an alternative method based on the temporal evolution of the magnon density at the beginning of an applied current pulse at which the magnon density deviates from the thermal level. Since this method does not depend on the signal-to-noise ratio, it allows for a robust and reliable determination of the threshold current which is important for the characterization of any future application based on the spin-transfer-torque effect.

  58. Magnetocardiography and magnetoencephalography measurements at room temperature using tunnel magneto-resistance sensors 査読有り

    Kosuke Fujiwara, Mikihiko Oogane, Akitake Kanno, Masahiro Imada, Junichi Jono, Takashi Terauchi, Tetsuo Okuno, Yuuji Aritomi, Masahiro Morikawa, Masaaki Tsuchida, Nobukazu Nakasato, Yasuo Ando

    Applied Physics Express 11 023001 2018年1月

  59. Structural and Magnetic Properties in Mn2VAl Full-Heusler Epitaxial Thin Films 査読有り

    Kenji Fukuda, Mikihiko Oogane, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 53 (11) 2017年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2017.2697078  

    ISSN:0018-9464

    eISSN:1941-0069

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    Epitaxially grown Mn2VAl full-Heusler thin films were fabricated on single crystalline MgO (001) substrates by using an ultrahigh-vacuum magnetron sputtering technique. X-ray diffraction revealed that epitaxial Mn2VAl films with a highly L2(1)-ordered structure were obtained by annealing around 600 degrees C. For the films deposited without a buffer layer and annealed at 500 degrees C-600 degrees C, the saturation magnetization was about 240 emu/cm(3) at 300 K, which was close to the theoretical value. The effective magnetic damping constant of Mn2VAl thin films was investigated using the ferromagnetic resonance technique. The effective damping constant was much larger than expected due to the inhomogeneity in the Mn2VAl films.

  60. Observation of Magnetoresistance Effect in n-Type Non-Degenerate Germanium With Co2Fe0.4Mn0.6Si Heusler Alloy Electrodes 査読有り

    Takeo Koike, Mikihiko Oogane, Tetsurou Takada, Hidekazu Saito, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 53 (11) 2017年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2017.2704780  

    ISSN:0018-9464

    eISSN:1941-0069

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    The local 3-terminal magnetoresistance properties of n-Ge/MgO/Co2Fe0.4Mn0.6Si lateral spin-valve devices were systematically investigated. In the spin extraction condition, clear steep voltage changes were successfully observed. We measured the bias voltage and temperature dependences of the spin resistance-area product. At a high bias voltage, the spin signal increased with increasing voltage, reaching a maximum value of 7.0 Omega mu m(2) at V-bias = 663 mV. The signal decreased with increasing temperature but was still observed up to 160 K.

  61. Magnetic sensor based on serial magnetic tunnel junctions for highly sensitive detection of surface cracks 査読有り

    Zhenhu Jin, Mikihiko Oogane, Kosuke Fujiwara, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 122 (17) 113903 2017年11月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5001098  

    ISSN:0021-8979

    eISSN:1089-7550

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    Magnetic tunnel junctions (MTJs) that consist of two ferromagnets separated by a thin insulator are among the core devices used in spintronic applications such as magnetic sensors. Since magnetic sensors require high sensitivity for nondestructive eddy current testing, we developed and demonstrated magnetic sensors based on various configurations of serial MTJs. We fabricated sensors with 4, 16, 28, 40, and 52 serial MTJs in various numbers of rows (1, 4, 7, 10, and 13) to detect surface cracks via eddy current testing. All of the sensors could detect and discriminate between surface cracks 0.1 mm in width and 0.1 to 1.0 mm in depth on an aluminum specimen. Systematic studies on the effect of the number of MTJs showed a signal to noise ratio as high as 115 dB when detecting 0.1 mm deep cracks with 28 serial MTJs in 7 rows. This suggests that suitably configured serial MTJ sensors can offer an excellent performance in the detection of tiny surface defects via eddy current testing. Published by AIP Publishing.

  62. DC Bias Reversal Behavior of Spin-Torque Ferromagnetic Resonance Spectra in CoFeB/MgO/CoFeB Perpendicular Magnetic Tunnel Junction 査読有り

    Tian Yu, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 53 (9) 2017年9月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2017.2707081  

    ISSN:0018-9464

    eISSN:1941-0069

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    Spin-torque ferromagnetic resonance (ST-FMR) spectra of nano-scaled CoFeB/MgO/CoFeB full perpendicular magnetic tunnel junctions (p-MTJs) were investigated, especially in detail at low dc-bias voltage region. Usually in in-plane magnetized MTJs (i-MTJs), the ST-FMR spectrum line shape reverses its symmetry as switching dc-bias voltage polarities; however, it is found that in the p-MTJs the line shape reversal behaves differently, that not only the spectrum shows anti-symmetric line shape at zero dc bias but also the dependence of reversal symmetry on dc bias is broken. Based on the framework of homodyne-detected ST-FMR, we extracted the parameters characterizing the spectra and discussed the possible factors resulting these differences.

  63. Wide-dynamic-range magnetic sensor based on magnetic tunnel junctions using perpendicularly magnetized synthetic antiferromagnetic reference layer 査読有り

    T. Nakano, M. Oogane, T. Furuichi, Y. Ando

    2017 IEEE International Magnetics Conference, INTERMAG 2017 2017年8月10日

    出版者・発行元:Institute of Electrical and Electronics Engineers Inc.

    DOI: 10.1109/INTMAG.2017.8007558  

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    Magnetic tunnel junctions (MTJs) with an MgO barrier, which exhibit a giant tunnel magnetoresistance (TMR) effect [1]-[4], have been intensively studied for application to various magnetic sensors in the automotive industry.

  64. Magnetic properties of ferrimagnetic (Mn1-xCox)2VAl full-Heusler epitaxial thin films 査読有り

    K. Fukuda, M. Oogane, Y. Ando

    2017 IEEE International Magnetics Conference, INTERMAG 2017 2017年8月10日

    出版者・発行元:Institute of Electrical and Electronics Engineers Inc.

    DOI: 10.1109/INTMAG.2017.8007971  

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    Half-metallic ferrimagnets have attracted many scientists as an ideal source of spin injection because of high spin polarization and low magnetization, which can realize small energy consumption in spintronic devices, such as magnetic random access memory (MRAM).

  65. L1

    Oogane Mikihiko, Watanabe Kenta, Saruyama Haruaki, Hosoda Masaki, Shahnaz Parvin, Kurimoto Yuta, Kubota Miho, Ando Yasuo

    Jpn. J. Appl. Phys. 56 (8) 0802A2 2017年6月1日

    出版者・発行元:Institute of Physics

    DOI: 10.7567/JJAP.56.0802A2  

    ISSN:0021-4922

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    L1<inf>0</inf>-ordered MnAl thin films were epitaxially grown by sputtering. The film composition dependences of structural and magnetic properties were systematically investigated in the MnAl thin films. Both the L1<inf>0</inf>-ordered parameter and the perpendicular magnetic anisotropy energy strongly depended on the composition of the MnAl thin films. The MnAl thin films with a Mn composition of 53–54 at. % showed both the highest L1<inf>0</inf>-ordered parameter and the perpendicular magnetic anisotropy. The substrate and annealing temperatures were optimized to improve the magnetic properties and surface morphology. We have fabricated MnAl thin films with both a very high K<inf>u</inf>of 12 × 10<sup>6</sup>erg/cm<sup>3</sup>and a small surface roughness of ca. 0.2 nm by optimizing the film composition and substrate and annealing temperatures. These results are useful guidelines for the fabrication of highly L1<inf>0</inf>-ordered MnAl thin films with a large perpendicular magnetic anisotropy.

  66. Cobalt substituted L1

    Watanabe Kenta, Oogane Mikihiko, Ando Yasuo

    Jpn. J. Appl. Phys. 56 (8) 0802B1 2017年6月1日

    出版者・発行元:Institute of Physics

    DOI: 10.7567/JJAP.56.0802B1  

    ISSN:0021-4922

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    The Co composition dependences of the structural and magnetic properties of L1<inf>0</inf>-(MnAl)<inf>1−</inf><inf>x</inf>Co<inf>x</inf>alloy films were investigated. The lattice constants of (MnAl)<inf>1−</inf><inf>x</inf>Co<inf>x</inf>films gradually changed with increasing Co content while maintaining the L1<inf>0</inf>-ordered structure below x = 0.08. The saturation magnetization gradually decreased with increasing Co content, and perpendicular magnetic anisotropy was observed below x = 0.08. In addition, Co substitution markedly improved the surface roughness of the films by decreasing the substrate temperature of (MnAl)<inf>1−</inf><inf>x</inf>Co<inf>x</inf>films. We found that both a high magnetic anisotropy and a small surface roughness can be obtained by the substitution of Co atoms into MnAl films.

  67. Grain-Size-Dependent Low-Temperature Electrical Resistivity of Polycrystalline Co2MnAl Heusler Alloy Thin Films 査読有り

    Resul Yilgin, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 30 (6) 1577-1584 2017年6月

    出版者・発行元:SPRINGER

    DOI: 10.1007/s10948-016-3957-5  

    ISSN:1557-1939

    eISSN:1557-1947

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    Low-temperature electrical resistivity of Co2MnAl Heusler alloy thin films prepared by DC magnetron sputtering technique has been investigated. After deposition of Co2MnAl thin films, they were annealed at 200-400 C-ay to control the crystal structure and the atomic order between Co, Mn, and Al sites. The ratio of intensity of (200) and (220) XRD peaks increases with increasing annealing temperature. The low-temperature dependence of electrical resistivity demonstrated that the film structure and magnetic ordering effected to the resistivity of Co2MnAl. The temperature dependence of resistivity for all samples has demonstrated the exponential decrease when temperature increases. However, 1000 (au)(1 /T) dependence of the logarithmic resistivity variation has not demonstrated the linear characteristic for all samples, and also, the temperature dependency of the deposited and annealed films has not been agreed with logarithmic, , behaviors. The temperature dependence of conductivity of samples has a relation with the square root of temperature. These kinds of behaviors have been attributed to grains/clusters and disordering of samples.

  68. Cobalt substituted L10-MnAl thin films with large perpendicular magnetic anisotropy 査読有り

    Kenta Watanabe, Mikihiko Oogane, Yasuo Ando

    Jpn. J. Appl. Phys. 2017年6月

  69. Estimation of surface crack dimensional characteristics by an eddy current method using a single magnetic tunnel junction device 査読有り

    Z. Jin, M. Abe, M. Oogane, K. Fujiwara, Y. Ando

    Jpn. J. Appl. Phys. 56 (7) 73001-73001 2017年6月

    出版者・発行元:Institute of Physics

    DOI: 10.7567/JJAP.56.073001  

    ISSN:0021-4922

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    Eddy current testing plays a significant role in detecting surface defects in a nondestructive testing field. The magnetoresistive sensors based on magnetic tunnel junction devices attracted considerable attention for their use in eddy current testing owing to their high sensitivity and capability of being miniaturized. We investigated the detection of surface cracks in eddy current testing using a single magnetic tunnel junction. A perpendicular component with a secondary magnetic field from an eddy current was measured by using an optimized rectangular magnetic tunnel junction device with an aspect ratio of 4 (20 × 80 µm<sup>2</sup>). Furthermore, according to the extracted ΔX and ΔV from the sensor output signal, surface cracks with various widths (0.1, 0.3, and 0.5 mm) and depths (0.5, 1.0, 1.5, and 3.0 mm) in aluminum specimens were successfully estimated using the magnetic tunnel junction device in eddy current testing when an excitation frequency of 1000 Hz was used.

  70. L10-ordered MnAl thin films with high perpendicular magnetic anisotropy 招待有り 査読有り

    Mikihiko Oogane, Kenta Watanabe, Haruaki Saruyama, Masaki Hosoda, Parvin Shahnaz, Yuta Kurimoto, Miho Kubota, Yasuo Ando

    Jpn. J. Appl. Phys. 2017年6月

  71. Fabrication of orientation-controlled nanocomposite Nd2Fe14B/Mo/α–Fe multilayer films 査読有り

    K. Kobayashi, D. Ogawa, K. Koike, H. Kato, M. Oogane, T. Miyazaki, Y. Ando, M. Itakura

    Journal of Physics, Conference series 2017年

    出版者・発行元:IOP Institute of Physics

  72. Experimental Investigation of the Temperature-Dependent Magnon Density and Its Influence on Studies of Spin-Transfer-Torque-Driven Systems 査読有り

    Thomas Meyer, Thomas Braecher, Frank Heussner, Alexander A. Serga, Hiroshi Naganuma, Koki Mukaiyama, Mikihiko Oogane, Yasuo Ando, Burkard Hillebrands, Philipp Pirro

    IEEE MAGNETICS LETTERS 8 318005 2017年

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/LMAG.2017.2734773  

    ISSN:1949-307X

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    We present the temperature dependence of the thermal magnon density in a thin ferromagnetic layer. By employing Brillouin light scattering and varying the temperature, an increase of the magnon density accompanied by a lowering of the spin-wave frequency is observed with increasing temperature. The magnon density follows the temperature according to the Bose-Einstein distribution function, which leads to an approximately linear dependency. In addition, the influence of this effect in spin-transfer-torque-driven systems is presented. In particular, the increase in the magnon density with temperature sets the limit for a suppression of magnons in charge current-driven systems. Hence, the maximum possible suppression of thermal magnons occurs at a finite current.

  73. Magnetic tunnel junctions using perpendicularly magnetized synthetic antiferromagnetic reference layer for wide-dynamic-range magnetic sensors 査読有り

    T. Nakano, M. Oogane, T. Furuichi, Y. Ando

    APPLIED PHYSICS LETTERS 110 (1) 2017年1月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4973462  

    ISSN:0003-6951

    eISSN:1077-3118

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    We developed CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with a perpendicularly magnetized synthetic antiferromagnetic (p-SAF) reference layer for magnetic sensor applications. The MTJs exhibited linear tunnel magnetoresistance curves to out-of-plane applied magnetic fields with dynamic ranges more than +/- 2.5 kOe, which are wider than those in CoFeB/MgO/CoFeB-MTJs reported to date. The performance metrics of MTJ sensors, i.e., sensitivity and nonlinearity, depend significantly on the anisotropy field of the free layer. We explained the dependences by a simple model based on the Stoner-Wohlfarth and Slonczewski models, which gives us a guideline to design the sensor performance metrics. These findings demonstrated that MTJs with a p-SAF reference layer are promising candidates for wide-dynamic-range magnetic sensors. Published by AIP Publishing.

  74. Investigation of magnetic sensor properties of magnetic tunnel junctions with superparamagnetic free layer at low frequencies for biomedical imaging applications 査読有り

    Kyohei Ishikawa, Mikihiko Oogane, Kousuke Fujiwara, Junichi Jono, Masaaki Tsuchida, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 55 (12) 2016年12月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.55.123001  

    ISSN:0021-4922

    eISSN:1347-4065

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    The magnetic sensor properties of magnetic tunnel junctions (MTJs) with a superparamagnetic (SP) free layer were systematically investigated at low frequencies (&lt;10 Hz). We prepared four varieties of MTJs with various SP properties by changing the annealing temperature. The temperature dependence of magnetoresistance curves and the signal/noise property at 285K were evaluated. We found that the SP free layer has the advantage of detecting very small and low-frequency AC magnetic fields compared with a ferromagnetic free layer. The SP free layer strongly suppressed magnetic 1/f noise at low frequencies and expressed a very linear response to a small magnetic field. The obtained properties in MTJs with the SP free layer are suitable for detecting biomagnetic fields. The detectivity was 111 nT at low frequencies (from 0.1 to 10Hz), which is one of the highest values in single-MTJ sensors. (C) 2016 The Japan Society of Applied Physics

  75. Influence of L1(0) order parameter on Gilbert damping constants for FePd thin films investigated by means of time-resolved magneto-optical Kerr effect 査読有り

    Satoshi Iihama, Akimasa Sakuma, Hiroshi Naganuma, Mikihiko Oogane, Shigemi Mizukami, Yasuo Ando

    PHYSICAL REVIEW B 94 (17) 174425 2016年11月

    DOI: 10.1103/PhysRevB.94.174425  

  76. Fabrication of highly ordered Co2Fe0.4Mn0.6Si Heusler alloy films on Si substrates 査読有り

    Takeo Koike, Mikihiko Oogane, Atsuo Ono, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 55 (8) 2016年8月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.55.088001  

    ISSN:0021-4922

    eISSN:1347-4065

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    The structural and magnetic properties of Si(100)/MgO/Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy thin films were systematically investigated. Highly B2-ordered CFMS Heusler films with an ordering parameter of ca. 70-80% were obtained by both the insertion of a very thin Mg layer into the Si/MgO interfaces to prevent oxidation of the Si surface and the optimization of the annealing temperature for the CFMS films. The prepared CFMS films exhibited high magnetization close to that of the CFMS bulk. Such highly B2-ordered CFMS films are very useful for realizing high spin injection efficiency in Si because of the half-metallicity of the CFMS films. (C) 2016 The Japan Society of Applied Physics.

  77. Effect of annealing on Curie temperature and phase transition in La0.55Sr0.08Mn0.37O3 epitaxial films grown on SrTiO3 (100) substrates by reactive radio frequency magnetron sputtering 査読有り

    T. Ichinose, H. Naganuma, T. Miyazaki, M. Oogane, Y. Ando, T. Ueno, N. Inami, K. Ono

    MATERIALS CHARACTERIZATION 118 37-43 2016年8月

    出版者・発行元:ELSEVIER SCIENCE INC

    DOI: 10.1016/j.matchar.2016.05.002  

    ISSN:1044-5803

    eISSN:1873-4189

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    Mn-poor LaSrMnO3 (LSMO) epitaxial films were grown on SrTiO3 (100) substrates by radio frequency magnetron sputtering in an argon and oxygen gas mix, and then the samples were annealed in air at various temperatures (T-a). 2 theta-chi X-ray diffraction mapping, nano-beam diffraction analysis through transmission electron microscopy, and electron back scatter diffraction through scanning electron microscopy revealed that -the crystal symmetry of the LSMO films changed from monoclinic/orthorhombic to rhombohedral on annealing in air. Curie temperature (T-C) of the LSMO films was found to increase with increasing T-a, and become higher than the room temperature at T-a &gt;= 861 degrees C, indicating that the cause of these changes was the filling of oxygen and the transition of the crystal symmetry into rhombohedral. (C) 2016 Elsevier Inc. All rights reserved.

  78. Magnetic Tunnel Junctions With [Co/Pd]-Based Reference Layer and CoFeB Sensing Layer for Magnetic Sensor 査読有り

    Takafumi Nakano, Mikihiko Oogane, Takamoto Furuichi, Kenichi Ao, Hiroshi Naganuma, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 52 (7) 2016年7月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2016.2518188  

    ISSN:0018-9464

    eISSN:1941-0069

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    We investigated the tunneling magnetoresistance (TMR) properties for the magnetic sensor application in MgO-based magnetic tunnel junctions (MTJs) using a perpendicularly magnetized [Co/Pd]-based reference layer and an in-plane magnetized CoFeB sensing layer with various thicknesses (t(CoFeB)). Linear TMR curves to an out-of-plane magnetic field were successfully obtained with a dynamic range of more than 600 Oe, corresponding to the coercivity of the [Co/Pd]-based reference layer. The MTJs showed the highest sensitivity of 0.026%/Oe for t(CoFeB) = 1.8 nm and the smallest nonlinearity of 0.11% full scale for t(CoFeB) = 3 nm. We clarified that the sensitivity and the nonlinearity in the MTJs are significantly associated with tCoFeB, which is attributed to the change in the anisotropy field of the CoFeB sensing layer.

  79. Magnetic field-controlled hysteresis loop bias in orthogonal exchange-spring coupling composite magnetic films 査読有り

    Jun Jiang, Tian Yu, Rui Pan, Qin-Tong Zhang, Pan Liu, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Xiufeng Han

    APPLIED PHYSICS EXPRESS 9 (6) 2016年6月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.9.063003  

    ISSN:1882-0778

    eISSN:1882-0786

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    The exchange bias (EB) is an effective fundamental and applicational method to realize magnetic hysteresis loop shifting. However, further manipulation of EB unidirectional anisotropy is difficult after setup using either field deposition or post-annealing. In this work, we experimentally show a new approach to control the magnetic hysteresis loop bias in a[ Co(0.2)/Pd(1)](5)/CoFeB orthogonal exchange-spring (ES) coupling system, where the direction and strength of unidirectional anisotropy can be easily manipulated by applying an external magnetic field. (C) 2016 The Japan Society of Applied Physics

  80. Observation of single-spin transport in an island-shaped CoFeB double magnetic tunnel junction prepared by magnetron sputtering 査読有り

    Thamrongsin Siripongsakul, Hiroshi Naganuma, Andras Kovacs, Amit Kohn, Mikihiko Oogane, Yasuo Ando

    PHILOSOPHICAL MAGAZINE 96 (4) 310-319 2016年2月

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/14786435.2015.1131343  

    ISSN:1478-6435

    eISSN:1478-6443

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    The Co40Fe40B20(CFB)/MgO/CFB/MgO/CFB-based multilayer was prepared by conventional magnetron sputtering and utilised in the fabrication of double magnetic tunnel junctions (DMTJs) for which the middle CFB layers were island-shaped. By analysing the magnetic property of the CFB islands with Langevin's equation, it was possible to identify their diameters of 7.6, 8.9 and 11.0nm; accordingly submicron-scaled DMTJs were fabricated to investigate single-spin transport phenomena. The coulomb staircase and the oscillatory tunnel magnetoresistive (TMR) were able to be observed at 6K, where the TMR ratio was enhanced up to 60%, which is the highest value ever achieved in this structure.

  81. Controlling Magnetization Switching and DC Transport Properties of Magnetic Tunnel Junctions by Mircowave Injection 査読有り

    Cheng Xin, Yu Guo Liu, Lin Shi, Tian Yu, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    7TH IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE (INEC) 2016 2016年

    出版者・発行元:IEEE

    ISSN:2159-3523

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    Searching new approaches to combine spintronic devices and microwave applications is a fascinating topic. On one hand, the application of spintronic devices opens new roads to generate and detect microwave in wide frequency range, on the other hand, applying/injection microwave also modulates the spintronic devices properties. In this report, we present our recent work on effects of MW injection on the switching properties of magnetic tunneling junctions (MTJs). Magnetic tunneling junction is a promising device cell choice for spintronic applications, such as magnetic sensors, nonvolatile magnetic random access memories, and magnetic logical. As the MTJ cell size approaches to nanoscale, magnetic materials with large magnetic anisotropy are usually adopted as MTJ magnetic electrodes to keep the thermal stability. This usually inevitably increases magnetization switching field or spin transfer torque switching current density. Therefore, searching methods to assist MTJ magnetization switching becomes important for practical applications. Here, we show that directly injecting microwave current into MTJ and taking advantage of microwave current induced spin transfer torque (STT) effect can assist magnetization switching effectively. Since microwave current rather than MW magnetic field is utilized, it enables us to control the switching assistance electrically and eliminates cross-talking between neighboring cells.

  82. Ultrafast demagnetization of L1(0) FePt and FePd ordered alloys 査読有り

    Satoshi Iihama, Yuta Sasaki, Hiroshi Naganuma, Mikihiko Oogane, Shigemi Mizukami, Yasuo Ando

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 49 (3) 2016年1月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/49/3/035002  

    ISSN:0022-3727

    eISSN:1361-6463

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    The cause of the time scale for ultrafast demagnetization induced by irradiation using a fs pulse laser remains an open issue. Spin-flip mediated by electron-phonon scattering due to spin-orbit interactions is one major theory proposed to explain ultrafast demagnetization. Ultrafast demagnetization in Ni, FePd, and FePt films was investigated in order to systematically study the influence of heavy elements on the demagnetization time. The ultrafast demagnetization in these systems was analyzed using the microscopic three temperature model, which is a theory based on spin-flip mediated by electron-phonon scattering. The spin-flip probability (a(sf)) values for the Ni, FePd, and FePt films were evaluated in the low pump fluence regime. It was found that the a(sf) value for the Ni film was larger than that for the FePd and FePt films. Thus, there is no correlation between the a(sf) value and the spin-orbit coupling strength. Fast demagnetization of the FePd film was also observed due to large electron-phonon scattering. In addition, it was found that the a(sf) values decreased with increasing magnetization quenching for all the films.

  83. Modification of the Interface Nanostructure and Magnetic Properties in Nd-Fe-B Thin Films 査読有り

    Kunihiro Koike, Takanao Kusano, Daisuke Ogawa, Keisuke Kobayashi, Hiroaki Kato, Mikihiko Oogane, Takamichi Miyazaki, Yasuo Ando, Masaru Itakura

    NANOSCALE RESEARCH LETTERS 11 2016年1月

    出版者・発行元:SPRINGER

    DOI: 10.1186/s11671-016-1227-x  

    ISSN:1556-276X

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    The effects of Nd2Fe14B grain size and Nd coating on the coercivity in sputter-deposited Nd-Fe-B/Nd thin films have been investigated in order to gain an insight into the coercivity mechanism of Nd-Fe-B magnets. Highly textured Nd2Fe14B particles were grown successfully on the MgO(100) single-crystal substrate with the Mo underlayer. As the Nd-Fe-B layer thickness t(NFB) was decreased from 70 to 5 nm, the coercivity H-c increased gradually from 6.5 to 16 kOe. By depositing the Nd overlayer onto these films and post-annealing at 500 degrees C, the H-c value further increased from 17.5 kOe (t(NFB) = 70 nm) to 26.2 kOe (t(NFB) = 5 nm). The amount of H-c increase by the combination of the Nd coating and post-annealing was about 10 kOe irrespective of the t(NFB) value. These results therefore suggest an independence of size and interface effects on the coercivity of Nd-Fe-B magnets.

  84. Systematic Investigation on Correlation Between Sensitivity and Nonlinearity in Magnetic Tunnel Junction for Magnetic Sensor 査読有り

    Takafumi Nakano, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 51 (11) 2015年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2015.2448723  

    ISSN:0018-9464

    eISSN:1941-0069

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    We fabricated magnetic tunnel junctions (MTJs) with a perpendicularly magnetized Co-Fe-B sensing layer for magnetic sensor applications exhibiting a linear tunneling magnetoresistance behavior, and systematically investigated correlation between sensitivity and nonlinearity in the MTJs. The experimental results in the MTJs annealed at different temperatures with various thicknesses and compositions of the Co-Fe-B sensing layer were compared with the simple calculation based on the Stoner-Wohlfarth model, which predicts the tradeoff relationship between the sensitivity and the nonlinearity. We found the clear tradeoff correlation between them regardless the annealing temperature and the composition of the Co-Fe-B sensing layer. These results show us a guideline for designing the sensing properties of magnetic sensors based on MTJs.

  85. The effect of atomic structure on interface spin-polarization of half-metallic spin valves: Co2MnSi/Ag epitaxial interfaces 査読有り

    Zlatko Nedelkoski, Philip J. Hasnip, Ana M. Sanchez, Balati Kuerbanjiang, Edward Higgins, Mikihiko Oogane, Atsufumi Hirohata, Gavin R. Bell, Vlado K. Lazarov

    APPLIED PHYSICS LETTERS 107 (21) 2015年11月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4936630  

    ISSN:0003-6951

    eISSN:1077-3118

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    Using density functional theory calculations motivated by aberration-corrected electron microscopy, we show how the atomic structure of a fully epitaxial Co7MnSi/Ag interfaces controls the local spin-polarization. The calculations show clear difference in spin-polarization at Fermi level between the two main types: bulk-like terminated Co/Ag and Mn-Si/Ag interfaces. Co/Ag interface spin-polarization switches sign from positive to negative, while in the case of Mn-Si/Ag, it is still positive but reduced. Cross-sectional atomic structure analysis of Co,MnSi/Ag interface, part of a spin-valve device, shows that the interface is determined by an additional layer of either Co or Mn. The presence of an additional Mn layer induces weak inverse spin-polarisation (-7%), while additional Co layer makes the interface region strongly inversely spin-polarized (-73%). In addition; we show that Ag diffusion from the spacer into the Co,MnSi electrode does not have a significant effect on the overall Co2MnSi /Ag performance. (C) 2015 AIP Publishing LLC.

  86. Negative exchange coupling in Nd2Fe14B(100)/α-Fe interface 査読有り

    Daisuke Ogawa, Kunihiro Koike, Shigemi Mizukami, Takamichi Miyazaki, Mikihiko Oogane, Yasuo Ando, Hiroaki Kato

    Appl. Phys. Lett. 107 (10) 2015年9月

    出版者・発行元:None

    DOI: 10.1063/1.4930829  

    ISSN:0003-6951

    eISSN:1077-3118

  87. Intrinsic Gilbert damping constant in epitaxial Co2Fe0.4Mn0.6Si Heusler alloys films 査読有り

    A.L. Kwilu, M. Oogane, H. Naganuma, M. Sahashi, Y. Ando

    J. Appl. Phys. 117 17D140 2015年4月

  88. Magnetic damping constant in Co-based full heusler alloy epitaxial films 査読有り

    M. Oogane, T. Kubota, H. Naganuma, Y. Ando

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 (16) 164012 2015年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/48/16/164012  

    ISSN:0022-3727

    eISSN:1361-6463

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    Co-based full-Heusler alloys, such as Co2MnSi and Co2MnGe, are expected to be used as half-metallic ferromagnetic material, which has complete spin polarization. They are the most promising materials for realizing half-metallicity at room temperature due to their high Curie temperature. The optimization of the magnetic damping constant of ferromagnetic materials is extremely important for achieving high-speed magnetization switching and reducing critical current density for spin torque transfer switching. We have systematically investigated the magnetic damping constant in Co-based full Heusler alloy epitaxial films. We found that the Gilbert damping constant seems to be roughly proportional to the total density of states at the Fermi level (E-F) by first principle calculation. A very small magnetic damping constant of 0.003 in the Co2Fe0.4Mn0.6Si epitaxial film was demonstrated. The small magnetic damping constant in Co2FexMn1-xSi films with x &lt; 0.6 can be attributed to the half-metallicity of Heusler alloys. Co-based full Heusler alloys with both half-metallicity and small magnetic damping will be very useful for future applications based on spintronic devices.

  89. All-optical characterisation of the spintronic Heusler compound Co2Mn0.6Fe0.4Si 査読有り

    Thomas Sebastian, Yuki Kawada, Bjoern Obry, Thomas Braecher, Philipp Pirro, Dmytro A. Bozhko, Alexander A. Serga, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Burkard Hillebrands

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 (16) 164015 2015年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/48/16/164015  

    ISSN:0022-3727

    eISSN:1361-6463

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    This article is devoted to the evaluation of the material parameters of the Heusler compound Co2Mn0.6Fe0.Si-4 via Brillouin light scattering spectroscopy. Recently, cobalt-based Heusler compounds and, in particular, the compound Co2Mn0.6Fe0.4Si have attracted huge interest in the fields of spintronics and magnon spintronics. Thus, evaluation of the material parameters that govern spin dynamics in the gigahertz regime is essential to develop and understand advanced experimental scenarios as well as potential technical applications. We demonstrate the evaluation of these parameters based on wavevector as well as time-resolved Brillouin light scattering spectroscopy. The focus of our study is the determination of the spin-wave damping in an individual microstructure as wells as of the exchange constant of Co2Mn0.6Fe0.4Si-parameters, that are difficult to estimate with alternative techniques.

  90. Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds 査読有り

    Daniel Steil, Oliver Schmitt, Roman Fetzer, Takahide Kubota, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Steven Rodan, Christian G. F. Blum, Benjamin Balke, Sabine Wurmehl, Martin Aeschlimann, Mirko Cinchetti

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 (16) 164016 2015年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/48/16/164016  

    ISSN:0022-3727

    eISSN:1361-6463

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    Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics. Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1-xMnxSi. The local ordering is studied by Co-59 nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the differences in the electronic structure at the Fermi energy and in the heat diffusion of thin films and bulk crystals.

  91. Magnetization Dynamics and Damping for L10-FePd Thin Films with Perpendicular Magnetic Anisotropy 査読有り

    S. Iihama, M. Khan, H. Naganuma, M. Oogane, T. Miyazaki, S. Mizukami, Y. Ando

    J. Magn. Soc. Jpn 39 (2) 57-61 2015年3月

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.1501R004  

    ISSN:1882-2924

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    Magnetization dynamics and damping for FePd films were investigated using the all-optical time-resolved magneto-optical Kerr effect. We deposited 16-nm-thick FePd thin films on a single crystal MgO(001) substrate. Both in-plane magnetic anisotropy and perpendicular magnetic anisotropy (PMA) FePd films were fabricated using the magnetron sputtering method at various substrate temperatures <i>T</i><sub>s</sub>. The dependencies of magnetization dynamics on the external magnetic field angle at fixed external magnetic field strengths were analyzed. The effective damping constant, <i>α</i><sub>eff</sub>, for FePd films with PMA exhibited anisotropy, whereas the <i>α</i><sub>eff</sub> for FePd with in-plane magnetic anisotropy did not depend significantly on the field angle. A uniaxial crystalline magnetic anisotropy constant, <i>K</i><sub>u1</sub>, of 11 Merg/cm<sup>3</sup> and a minimum for <i>α</i><sub>eff</sub> of 0.007 were observed for film prepared at <i>T</i><sub>s</sub> = 200°C. This <i>α</i><sub>eff</sub> value was much smaller than that for other Fe- and Co-based materials with large PMA such as <i>L</i>1<sub>0</sub>-FePt alloy, Co/Pt(Pd) multilayers.

  92. Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy 査読有り

    Roman Fetzer, Benjamin Stadtmueller, Yusuke Ohdaira, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti

    SCIENTIFIC REPORTS 5 8537 2015年2月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/srep08537  

    ISSN:2045-2322

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    Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin-and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature.

  93. 生体磁場センサ応用に向けたホイスラー合金電極 強磁性トンネル接合の作製

    小野 敦央, 大兼 幹彦, 永沼 博, 安藤 康夫

    生体医工学 53 S187_01-S187_01 2015年

    出版者・発行元:一般社団法人 日本生体医工学会

    DOI: 10.11239/jsmbe.53.S187_01  

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    Magnetic tunnel junctions (MTJs) have great advantages for the magnetic field sensor applications. However, a significant improvement of tunnel magneto-resistance (TMR) ratio is needed to detect a small bio-magnetic field. In this study, we fabricated MTJs with half-metallic Co<sub>2</sub>Fe<sub>0.4</sub>Mn<sub>0.6</sub>Si(CFMS) Heusler alloy which are expected to increase TMR ratio. The fabricated MTJswere annealed twice to achieve sensor-type TMR curves. Figure shows the 2nd annealing temperature dependence of TMR curves. In MTJ annealed at 200℃, TMR curve showed a linear resistance response, which is required for sensor applications. This work was supported by the S-Innovation program, Japan Science and Technology Agency (JST).

  94. 生体磁場計測に向けた強磁性トンネル接合センサの作製とノイズ特性

    藤原 耕輔, 大兼 幹彦, 加藤 大樹, 城野 純一, 永沼 博, 桂田 弘之, 安藤 康夫

    生体医工学 53 S187_03-S187_03 2015年

    出版者・発行元:一般社団法人 日本生体医工学会

    DOI: 10.11239/jsmbe.53.S187_03  

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    MTJ is a small size device, working in room temperature with low power consumption, and is expected to enable detection of bio-magnetic field without liquid He. For the purpose of practical realization of MTJ bio-magnetic sensor, this study evaluated the signal and noise with various MgO barrier thicknesses in MTJ to reduce 1/f noise in frequency domain. Figures show MgO thickness dependence of signal voltage, noise voltage and S/N ratio measured from 18 Hz, 120 nT<sub>p-p</sub> input signal. Both signal and noise voltage increased with increasing MgO thickness. From this relation of signal and noise, maximum 154 S/N ratio was acquired by 2.2 nm MgO thickness.

  95. Electrical Detection of Millimeter-Waves by Magnetic Tunnel Junctions Using Perpendicular Magnetized L1(0)-FePd Free Layer 査読有り

    Hiroshi Naganuma, G. Kirn, Yuki Kawada, Nobuhito Inami, Kenzo Hatakeyama, Satoshi Iihama, Khan Mohammed Nazrul Islam, Mikihiko Oogane, Shigemi Mizukami, Yasuo Ando

    NANO LETTERS 15 (1) 623-628 2015年1月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/nl504114v  

    ISSN:1530-6984

    eISSN:1530-6992

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    Spin dynamics excited by spin-polarized current in magnetic tunnel junctions (MTJs) is potentially useful in nanoscale electrical oscillation sources and detection devices. A spin oscillator/detector should work at a high frequency, such as that of a millimeter-wave, where the quality of a semiconductor device is restricted by carrier mobility, the CR time constant, and so on. Developers of spin systems for practical use need to find out how to excite spin dynamics (i) in the millimeter-wave region, (ii) with low power consumption (ex: no external magnetic field, low damping material), and (iii) for broad frequency modulation. Here L1(0)-ordered FePd alloy with perpendicular magnetocrystalline anisotropy (PMA) and a low damping constant, 0.007, was used for the free layer in the MTJs, and a homodyne-detected ferromagnetic resonance (FMR) signal was obtained at around 30 GHz together with the possibility of one-octave frequency modulation. The FMR signal in out-of-plane magnetized L10-ordered FePd free layer could be excited without an external magnetic field by injecting in-plane spin polarized alternating current. This study shows the potential utility of L1(0)-ordered alloy materials such as FePt, CoPt, MnAl, and MnGa in a variety of millimeter-wave spin devices.

  96. Preparation of monoclinic 0.9(BiFeO3)-0.1(BiCoO3) epitaxial films on orthorhombic YAlO3 (100) substrates by r.f. magnetron sputtering 査読有り

    T. Ichinose, H. Naganuma, K. Mukaiyama, M. Oogane, Y. Ando

    JOURNAL OF CRYSTAL GROWTH 409 18-22 2015年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jcrysgro.2014.09.044  

    ISSN:0022-0248

    eISSN:1873-5002

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    0.9BiFeO(3)-0.1BiCoO(3) (BFCO) films (t = 100 nm) were prepared on orthorhombic YAlO3 (YAO) (100) substrates by r.f. magnetron sputtering. Film flatness, crystallinity, crystal symmetry, and secondary phase formation are strongly affected by the pressure of the sputtering gasses. Ar and O-2. Phi-scan measurements showed that the films were epitaxially grown on the substrates, with the crystal relation [101](p)(101)(p) BFCOII[101](p)( 101)(p) YAO. X-ray reciprocal space mapping revealed that the crystal symmetry of the BECO films was a pseudo-cubic-like monoclinic structure, with M-C phase, rather than the Cm symmetry of the bulk BFCO. Cross-sectional transmission electron microscopy analysis revealed that the film had, as a result of a lattice misfit of 7%, strong compressive strain less than 10 nm from the interface, which relaxed monotonically with increasing distance from the interface. Magnetic measurements show that strained monoclinic BFCO has smaller magnetization compared to rhombohedral BFCO. (C) 2014 Elsevier B.V. All rights reserved

  97. Optimization of Domain Wall Oscillations in Magnetic Nanowires 査読有り

    A. S. Demiray, H. Naganuma, M. Oogane, Y. Ando

    IEEE MAGNETICS LETTERS 6 3700104 2015年

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/LMAG.2014.2379629  

    ISSN:1949-307X

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    By properly choosing material parameters and geometry of a magnetic nanowire, pinned domain wall oscillations at a local constriction can be obtained at low current densities. The thickness modulation of the wire gives an additional uniaxial magnetic anisotropy, which modifies the transverse anisotropy energy that defines the critical current density required for the onset of domain wall oscillations. Broadband microwave signals are obtained with these values of current density.

  98. Penetration depth of transverse spin current in (001)-oriented epitaxial ferromagnetic films 査読有り

    Augustin L. Kwilu, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 368 333-337 2014年11月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2014.05.043  

    ISSN:0304-8853

    eISSN:1873-4766

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    We fabricated (001)-oriented epitaxial four-layered thin films of Cr/Co2MnSi/Cu/Co50Fe50 by dc magnetron sputtering in order to investigate the physical characteristics of the transverse spin current. The penetration depth lambda(T) characterizes the transverse spin current generated by the spin pumping effect that takes place in a film subjected to an external magnetic field. By analyzing the dependence on the Co50Fe50 thickness of the peak-to-peak line widths of ferromagnetic resonance, we determined AT within the Co50Fe50 layer and found it to be lambda(T) = 0.9 nm. (C) 2014 Elsevier B.V. All rights reserved.

  99. Non-Gilbert-damping Mechanism in a Ferromagnetic Heusler Compound Probed by Nonlinear Spin Dynamics 査読有り

    P. Pirro, T. Sebastian, T. Braecher, A. A. Serga, T. Kubota, H. Naganuma, M. Oogane, Y. Ando, B. Hillebrands

    PHYSICAL REVIEW LETTERS 113 (22) 227601 2014年11月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.113.227601  

    ISSN:0031-9007

    eISSN:1079-7114

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    The nonlinear decay of propagating spin waves in the low-Gilbert-damping Heusler film Co2Mn0.6Fe0.4Si is reported. Here, two initial magnons with frequency f(0) scatter into two secondary magnons with frequencies f(1) and f(2). The most remarkable observation is that f(1) stays fixed if f(0) is changed. This indicates, that the f(1) magnon mode has the lowest instability threshold, which, however, cannot be understood if only Gilbert damping is present. We show that the observed behavior is caused by interaction of the magnon modes f(1) and f(2) with the thermal magnon bath. This evidences a significant contribution of the intrinsic magnon-magnon scattering mechanisms to the magnetic damping in high-quality Heusler compounds.

  100. Low precessional damping observed for L1(0)-ordered FePd epitaxial thin films with large perpendicular magnetic anisotropy 査読有り

    S. Iihama, A. Sakuma, H. Naganuma, M. Oogane, T. Miyazaki, S. Mizukami, Y. Ando

    APPLIED PHYSICS LETTERS 105 (14) 142403 2014年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4897547  

    ISSN:0003-6951

    eISSN:1077-3118

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    High-quality L1(0) ordered 20 nm-thick FePd epitaxial thin films with a large perpendicular magnetic anisotropy were fabricated using a SrTiO3 substrate. The uniaxial crystalline magnetic anisotropy constant Ku evaluated for the films annealed above 500 degrees C was 14 Merg/cm(3). A very low effective damping constant, alpha(eff) = 0.007, was observed for FePd thin films annealed at 500 degrees C. This value is smaller than that of other Fe-based ordered alloys with a large perpendicular magnetic anisotropy. (C) 2014 AIP Publishing LLC.

  101. Present and perspective of bio-magnetic measurement using ferromagnetic tunnel junctions 査読有り

    Y. Ando, T. Nishikawa, K. Fujiwara, M. Oogane, D. Kato, H. Naganuma

    Transactions of Japanese Society for Medical and Biological Engineering 52 33-OS-34 2014年8月17日

    出版者・発行元:Japan Soc. of Med. Electronics and Biol. Engineering

    DOI: 10.11239/jsmbe.52.OS-33  

    ISSN:1347-443X 1881-4379

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    Currently, SQUID is the most sensitive of the magnetic sensor and is used for the measurement of biological fields. However, dissemination of the device to the medical field realistically is very strict due to the big size of the device, in terms of introduction and maintenance costs. In particular, a dewar for holding a low temperature is required in order to immersion in liquid helium for operating the SQUID element. The distance of the dewar from the head surface, and also the dewar surface from the SQUID element, act as restraint for accurate measurement. This paper proposes a sensor for the biomagnetic field measurementwith magnetic tunnel junction (MTJ) devices. It can be operated at room temperature and is brought it into close contact with the head. We describe the necessary technical challenges toward its realizationand the feasibility in the future.

  102. Correlations between atomic structure and giant magnetoresistance ratio in Co-2(Fe, Mn) Si spin valves 査読有り

    L. Lari, K. Yoshida, P. L. Galindo, J. Sato, J. Sizeland, D. Gilks, G. M. Uddin, Z. Nedelkoski, P. J. Hasnip, A. Hirohata, M. Oogane, Y. Ando, V. K. Lazarov

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 47 (32) 322003 2014年8月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/47/32/322003  

    ISSN:0022-3727

    eISSN:1361-6463

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    We show that the magnetoresistance of Co2FexMn1-x Si-based spin valves, over 70% at low temperature, is directly related to the structural ordering in the electrodes and at the electrodes/spacer (Co2FexMn1-x Si/Ag) interfaces. Aberration-corrected atomic resolution Z-contrast scanning transmission electron microscopy of device structures reveals that annealing at 350 degrees C and 500 degrees C creates partial B-2/L(2)1 and fully L2(1) ordering of electrodes, respectively. Interface structural studies show that the Ag/Co2FexMn1-x Si interface is more ordered compared to the Co2FexMn1-x Si/Ag interface. The release of interface strain is mediated by misfit dislocations that localize the strain around the dislocation cores, and the effect of this strain is assessed by first principles electronic structure calculations. This study suggests that by improving the atomic ordering and strain at the interfaces, further enhancement of the magnetoresistance of CFMS-based current-perpendicular-to-plane spin valves is possible.

  103. Mode change of vortex core oscillation induced by large direct current in 120 nm sized current perpendicular-to-plane giant magnetoresistance devices with a perpendicular polarizer 査読有り

    Yuki Kawada, Hiroshi Naganuma, Ahmet Serdar Demiray, Mikihiko Oogane, Yasuo Ando

    APPLIED PHYSICS LETTERS 105 (5) 052407 2014年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4892077  

    ISSN:0003-6951

    eISSN:1077-3118

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    Current-induced microwave spectra were measured in small-sized giant magnetoresistance devices composed of a NiFe vortex free layer and an out-of-plane magnetized Co/Pd multilayer polarizer. The influence of a large direct current (DC) and a bias field on the excited mode of the free layer is systematically investigated. For small current values, microwave spectra due to the vortex core oscillation were observed around 1 GHz, while the frequency abruptly changed to 4-4.5 GHz at certain DC values. The experimental data were reproduced by micromagnetic simulation, which indicates that the mode change of the vortex core oscillation in the free layer is dominated by the Oersted field from the large DC. (C) 2014 AIP Publishing LLC.

  104. Preparation of a heteroepitaxial LaxSryMnzO3/BiFeO3 bilayer by r.f. magnetron sputtering with various oxygen gas flow ratios 査読有り

    H. Naganuma, T. Ichinose, H. A. Begum, S. Sato, X. F. Han, T. Miyazaki, In-T. Bae, M. Oogane, Y. Ando

    AIP ADVANCES 4 (8) 087133 2014年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4893998  

    ISSN:2158-3226

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    BiFeO3 (BFO) and La(x)Sr(y)MnzO(3) (LSMO) films were epitaxially grown on SrTiO3 (100) substrates by r.f. magnetron sputtering with various oxygen gas flow ratios (F-O2). Compositional ratios of each atom in both of BFO and LSMO could be controlled kept to around 10 at.% by changing F-O2. Adjusting the compositional ratio to La0.35Sr0.15Mn0.5O3 not only increase T-c of LSMO but also produces sufficient oxygen to form a perovskite lattice. For an LSMO/BFO heterostructure, detailed observation by cross sectional transmission electron microscopy (TEM) revealed that the lattice of rhombohedral (SG: R-3c) LSMO was shrank by a clamping effect from the SrTiO3 substrates, and then the BFO was grown in two layers: (i) an interfacial BFO layer (7 nm thick) with evenly shrunk a-axis and c-axis, and (ii) an upper BFO layer (25 nm thick) expanded along the c-axis. Neither misfit strain nor dislocations appeared at the interface between the shrunken BFO and LSMO layers, and these heterostructures did not show exchange bias. These results suggest that BFO is suitable for a tunneling barrier combine with LSMO electrode. (C) 2014 Author(s).

  105. Ultrafast magnetization dynamics in Co-based Heusler compounds with tuned chemical ordering 査読有り

    D. Steil, O. Schmitt, R. Fetzer, T. Kubota, H. Naganuma, M. Oogane, Y. Ando, A. K. Suszka, O. Idigoras, G. Wolf, B. Hillebrands, A. Berger, M. Aeschlimann, M. Cinchetti

    NEW JOURNAL OF PHYSICS 16 063068 2014年6月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1367-2630/16/6/063068  

    ISSN:1367-2630

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    We have studied thin film samples of Co2FeSi and Co2MnSi with different degrees of chemical ordering using the time-resolved magneto-optical Kerr effect to elucidate the influence of defects in the crystal structure on magnetization dynamics. Surprisingly, we find that the presence of defects does not influence the optically induced magnetization dynamics on the ultrashort timescale (some 100 fs). However, we observe a second demagnetization stage with a timescale of tens of picoseconds in Co2MnSi for low chemical ordering; that is, a large number of defects. We interpret this second demagnetization step as originating from scattering of mostly thermalized majority electrons into unoccupied minority defect states.

  106. Static and dynamic magnetic properties of cubic Mn-Co-Ga Heusler films 査読有り

    A. S. Demiray, T. Kubota, S. Iihama, S. Mizukami, T. Miyazaki, H. Naganuma, M. Oogane, Y. Ando

    JOURNAL OF APPLIED PHYSICS 115 (17) 2014年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4864250  

    ISSN:0021-8979

    eISSN:1089-7550

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    We investigated the static and dynamic magnetic properties of thin films of Mn-Co-Ga Heusler compound. Gilbert damping and exchange stiffness constants of the films were evaluated by using the ferromagnetic resonance technique in the X-band regime (f = 9.4 GHz). By analyzing the experimental spectra, magnetic parameters of the films such as the line width and the Gilbert damping were deduced, and the exchange stiffness constant was estimated from the perpendicular standing spin-wave resonance. The Gilbert damping constant was estimated to be 0.017 in a specific film composition. The exchange stiffness constant showed a linear dependence on the film composition. (C) 2014 AIP Publishing LLC.

  107. Tunnel magnetoresistance effect using perpendicularly magnetized tetragonal and cubic Mn-Co-Ga Heusler alloy electrode 査読有り

    T. Kubota, S. Mizukami, Q. L. Ma, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF APPLIED PHYSICS 115 (17) 2014年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4855016  

    ISSN:0021-8979

    eISSN:1089-7550

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    Epitaxially grown tetragonal and cubic Mn-Co-Ga thin films were fabricated onto single crystalline Cr (001) under a layer. High perpendicular magnetic anisotropy is achieved in the tetragonal Mn2.3Co0.4Ga1.3 film, and a small, unexpected perpendicular magnetic anisotropy was induced in the cubic Mn1.8Co1.2Ga1.0 film as well. The tunnel magnetoresistance (TMR) effect of the Mn-Co-Ga/MgO/CoFeB magnetic tunnel junctions (MTJs) were investigated. TMR ratios of 5% and 11% were observed at room temperature for the MTJs using tetragonal Mn2.3Co0.4Ga1.3 and cubic Mn1.8Co1.2Ga1.0 electrodes, respectively. The composition dependence is discussed briefly. (C) 2014 AIP Publishing LLC.

  108. Spin-dependent transport behavior in C-60 and Alq(3) based spin valves with a magnetite electrode (invited) 査読有り

    Xianmin Zhang, Shigemi Mizukami, Qinli Ma, Takahide Kubota, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 115 (17) 172608 2014年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4870154  

    ISSN:0021-8979

    eISSN:1089-7550

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    The spin-dependent transport behavior in organic semiconductors (OSs) is generally observed at low temperatures, which likely results from poor spin injection efficiency at room temperature from the ferromagnetic metal electrodes to the OS layer. Possible reasons for this are the low Curie temperature and/or the small spin polarization efficiency for the ferromagnetic electrodes used in these devices. Magnetite has potential as an advanced candidate for use as the electrode in spintronic devices, because it can achieve 100% spin polarization efficiency in theory, and has a high Curie temperature (850 K). Here, we fabricated two types of organic spin valves using magnetite as a high efficiency electrode. C-60 and 8-hydroxyquinoline aluminum (Alq(3)) were employed as the OS layers. Magnetoresistance ratios of around 8% and over 6% were obtained in C-60 and Alq(3)-based spin valves at room temperature, respectively, which are two of the highest magnetoresistance ratios in organic spin valves reported thus far. The magnetoresistance effect was systemically investigated by varying the thickness of the Alq(3) layer. Moreover, the temperature dependence of the magnetoresistance ratios for C-60 and Alq(3)-based spin valves were evaluated to gain insight into the spin-dependent transport behavior. This study provides a useful method in designing organic spin devices operated at room temperature. (C) 2014 AIP Publishing LLC.

  109. Gilbert damping constants of Ta/CoFeB/MgO(Ta) thin films measured by optical detection of precessional magnetization dynamics 査読有り

    Satoshi Iihama, Shigemi Mizukami, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    PHYSICAL REVIEW B 89 (17) 174416 2014年5月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.89.174416  

    ISSN:1098-0121

    eISSN:1550-235X

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    The magnetization dynamics of both Ta/CoFeB/MgO and Ta/CoFeB/Ta films were investigated using an all-optical pump-probe method. The magnetic field strength and the applied field direction dependencies of the precession frequency and the relaxation time were explained well by the Landau-Lifshitz-Gilbert equation when taking the magnetic anisotropy distribution in the film into account. The thickness dependence of the a values obtained for both stacked films was also discussed. The a values increased linearly with increasing inverse CoFeB thickness (t(CoFeB)). The slope of the a vs 1/t(CoFeB) characteristic for Ta/CoFeB/MgO films was smaller than that for Ta/CoFeB/Ta films, implying that the enhancement of a was caused by the CoFeB/Ta interface. Comparison of the annealing temperature dependence of a and the perpendicular magnetic anisotropy constant Ku revealed no correlation between a and Ku.

  110. Half-metal CPP GMR sensor for magnetic recording 査読有り

    Z. Diao, M. Chapline, Y. Zheng, C. Kaiser, A. Ghosh Roy, C. J. Chien, C. Shang, Y. Ding, C. Yang, D. Mauri, Q. Leng, M. Pakala, M. Oogane, Y. Ando

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 356 73-81 2014年4月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2013.12.050  

    ISSN:0304-8853

    eISSN:1873-4766

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    Current-perpendicular-to-plane (CPP) giant magnetoresistance in magnetic CoFeMnSi Heusler alloy based spin valves and its potential application for high areal density recording are investigated, given that film stack design and crystalline structure matching during film growth are considered. Modeling of electron transport in spin valves predicts the CPP GMR of up to 130% and 25% in pseudo and antiferromagnet pinned spin valves at large bulk diffusive scattering asymmetry in Heusler alloy layers. Experimentally, the testing structures of pseudo spin valves, which have the L2(1) ordered Huesler alloy layers grown on single crystal MgO substrates, were built and demonstrate the CPP GMR of 55% or larger with Delta RA &gt;= 27.5 m Omega mu m(2). CPP GMR reader sensors were fabricated based on antiferromagnet pinned spin valves using the same Huesler alloy materials albeit on AlTiC wafers, with narrow track widths of down to 35 nm. The CPP GMR obtained is up to 13% (18%, Delta RA=9.0 m Omega mu m(2) after correction of current distribution in device). Reader test results show that the low frequency track averaged output amplitude is 3.14 mV with the electrical SNR=28 dB. These read heads have the transition width of readback waveform T50 of similar to 22 am and the magnetic read track width of 35.6 nm. The obtained on-track bit error rate is close to 10(-3) decade at a linear density of 1800 KFCI, potentially realizing a magnetic recording with an areal density of up to 800 Gb/in(2). (C) 2013 Elsevier B.V. All rights reserved.

  111. B2 Atomic Disorder in Co<SUB>2</SUB>Fe<SUB>x</SUB>Mn<SUB>1-x</SUB>Si Heusler Alloys 査読有り

    P.J. Hasnip, C. H. Loach, J. H. Smith, M. I. J. Probert, D. Gilks, J. Sizeland, K. Yoshida, M. Oogane, A. Hirohata, V. K. Lazarov

    Journal of the Magnetics Society of Japan 38 50-55 2014年3月20日

    DOI: 10.3379/msjmag.1402R010  

  112. The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1-xSi Heusler Alloys 査読有り

    Philip J. Hasnip, Christian H. Loach, Joseph H. Smith, Matthew I. J. Probert, Daniel Gilks, James Sizeland, Leonardo Lari, James Sagar, Kenta Yoshida, Mikihiko Oogane, Atsufumi Hirohata, Vlado K. Lazarov

    MATERIALS 7 (3) 1473-1482 2014年3月

    出版者・発行元:MDPI AG

    DOI: 10.3390/ma7031473  

    ISSN:1996-1944

    eISSN:1996-1944

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    In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1-xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co-Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5-0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures.

  113. Development of Integrated Magnetic Tunnel Junctions for Detection of Bio-magnetic Field

    Nishikawa Takuo, Oogane Mikihiko, Fujiwara Kousuke, Kato Daiki, Naganuma Hiroshi, Ando Yasuo

    生体医工学 52 O-503-O-503 2014年

    出版者・発行元:Japanese Society for Medical and Biological Engineering

    DOI: 10.11239/jsmbe.52.O-503  

    ISSN:1347-443X

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    Although the biomagnetic field is useful to observe an organic activity and the superconducting quantum interference device (SQUID) is used to detect at the moment, there is a problem of needing a liquid helium in order to operate this SQUID. This research focuses attention on the ferromagnetic tunnel junction (MTJ) device which is operable in a room temperature, and aims at the reduction of the elements for using this MTJ device as a biomagnetic field sensor and the reduction of the circuit system noise.

  114. Fabrication of Magnetic Tunnel Junctions with Amorphous CoFeSiB for the Bio-magnetic Field Sensor Devices

    Kato Daiki, Oogane Mikihiko, Fujiwara Kosuke, Nishikawa Takuo, Naganuma Hiroshi, Ando Yasuo

    生体医工学 52 O-504-O-504 2014年

    出版者・発行元:Japanese Society for Medical and Biological Engineering

    DOI: 10.11239/jsmbe.52.O-504  

    ISSN:1347-443X

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    In magnetic tunnel junctions (MTJs), the resistance changes by external magnetic field through tunnel magnetoresistance (TMR) effect and MTJs can be applied to magnetic field sensors. To detect a small bio-magnetic field, we have to develop MTJs with high sensitivity (=TMR/2<I>H</I><SUB>k</SUB>, <I>H</I><SUB>k</SUB>: magnetic anisotropy field) of more than 100%/Oe, which is two digit larger than that of actual devices. In this work, MTJs with a low <I>H</I><SUB>k</SUB> CoFeSiB amorphous electrode was fabricated to realize such a highly sensitive magnetic sensor. After optimizing the preparation condition of CoFeSiB, a very high sensitivity of 40%/Oe was obtained. The result came much closer to our goal.

  115. Dependence of Magnetic Damping on Temperature and Crystal Orientation in Epitaxial Fe4N Thin Films 査読有り

    S. Isogami, M. Tsunoda, M. Oogane, A. Sakuma, M. Takahashi

    Journal of the Magnetics Society of Japan 38 (4) 162-168 2014年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.1406R001   10.3379/msjmag.1406r001  

    ISSN:1882-2924

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    In-plane and out-of-plane ferromagnetic resonance (FMR) were used to investigate the intrinsic magnetic damping constant (α) in epitaxial Fe<sub>4</sub>N thin films deposited on MgO substrates. The dependence of α on temperature was evaluated from room temperature (RT) to 4 K. The external magnetic field (<i>H</i>) of FMR was applied in two directions, i.e., [100] and [110], of the Fe<sub>4</sub>N lattice. Anisotropic α was observed from RT to 4 K. Moreover, the α for <i>H</i> // [100] exceeded the α for <i>H</i> // [110] at 180 K. Numerical calculations of α for bulk Fe<sub>4</sub>N revealed the same behavior as that in the experiments. The temperature dependence of anisotropic α was explained by the changes in the electronic band structure depending on the directions of magnetization.

  116. Fabrication of Integrated Magnetic Tunnel Junctions for Detection of Bio-magnetic Field 査読有り

    K. Fujiwara, M. Oogane, D. Kato, T. Nishikawa, H. Naganuma, Y. Ando

    Transactions of Japanese Society for Medical and Biological Engineering 52 O-505-505-O-506 2014年

    出版者・発行元:Japanese Society for Medical and Biological Engineering

    DOI: 10.11239/jsmbe.52.O-505  

    ISSN:1347-443X

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    Since MTJ sensor is an element of room temperature operation, low power consumption, low cost and small device size, thus it is expectable to spread widely the medical diagnostics and basic research using bio-magnetic fields. In this study, in order to reduce 1/<I>f</I> noise, 100x100 MTJ sensor arrays were fabricated. Figure shows the system of imperceptible magnetic filed detection. The magnetic field was generated with the one turn coil, using the sine wave of 123 Hz. The result is shown in figure. In this study, the detection of a magnetic field of 0.29 nT was demonstrated with fabricated 100x100 MTJ sensor array.

  117. Spin and symmetry properties of the buried Co2MnSi/MgO interface 査読有り

    R. Fetzer, Y. Ohdaira, H. Naganuma, M. Oogane, Y. Ando, T. Taira, T. Uemura, M. Yamamoto, M. Aeschlimann, M. Cinchetti

    58th Annual Conf. on Magnetism and Magnetic Materials, Abstracts 624 (GB-14) 2013年11月

  118. Fabrication of Magnetic Tunnel Junctions with Amorphous CoFeSiB Ferromagnetic Electrode for Magnetic Field Sensor Devices 査読有り

    Daiki Kato, Mikihiko Oogane, Kosuke Fujiwara, Takuo Nishikawa, Hiroshi Naganuma, Yasuo Ando

    APPLIED PHYSICS EXPRESS 6 (10) 2013年10月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.6.103004  

    ISSN:1882-0778

    eISSN:1882-0786

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    The magnetic tunnel junctions (MTJs) with a soft magnetic CoFeSiB amorphous electrode and a MgO barrier layer were fabricated. A double annealing process was carried out to obtain the linear resistance response to the external magnetic field. The effect of the annealing temperature on the sensitivity of magnetic sensors was systematically investigated. We achieved a high sensitivity of 40%/Oe, where the sensitivity is defined as TMR/(2H(k)), where TMR is the tunnel magnetoresistance ratio and H-k is the magnetic anisotropy field of the free layer of MTJs. (C) 2013 The Japan Society of Applied Physics

  119. Tunneling magnetoresistance effect in MnGa based perpendicular magnetic tunnel junction with Fe/Co interlayer 査読有り

    Qinli Ma, Shigemi Mizukami, Takahide Kubota, Xianmin Zhang, Atsushi Sugihara, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 114 (16) 2013年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4828483  

    ISSN:0021-8979

    eISSN:1089-7550

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    In order to enhance the magnetoresistance (MR) of perpendicular magnetic tunnel junctions (pMTJs) based on MnGa alloys, a single ferromagnetic layer such as Fe and Co was previously inserted between MnGa and MgO barrier. In this study, to further enhance the spin-filter effect, we introduced a Fe/Co bilayer as an interlayer in the MnGa/MgO interface. Compared to the single Co interlayer, an apparent MR ratio enhancement was obtained when Fe layer thickness was around 0.3 nm for pMTJs with MnGa compositions of Mn57Ga43, Mn62Ga38, and Mn70Ga30, and the maximum MR ratio reaches 50% at room temperature. In addition, inverted magnetoresistance loops were observed due to the antiparallel alignment of the magnetic moments of Co and MnGa layers separated by the thin Fe layer. (C) 2013 AIP Publishing LLC.

  120. The role of structure on magneto-transport properties of Heusler Co2MnSi films deposited on MgO(001) 査読有り

    N. Tal, D. Mogilyanski, A. Kovacs, H. Naganuma, S. Tsunegi, M. Oogane, Y. Ando, A. Kohn

    JOURNAL OF APPLIED PHYSICS 114 (16) 2013年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4826908  

    ISSN:0021-8979

    eISSN:1089-7550

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    We present an experimental study identifying structural reasons that degrade spin-polarization of Co2MnSi thin films deposited on MgO(001) substrates. Through the fabrication of magnetic tunnel junctions, we measure a range of values for tunneling magneto-resistance (TMR) ratios following post-deposition annealing and epitaxial crystallization of the Heusler film. These TMR ratios reflect qualitatively the change in spin polarization of the Co2MnSi thin films. Low-temperature annealing results in low spin-polarization due to a high fraction of an amorphous phase. As annealing temperatures increase, the fraction of L2(1) and B2 chemically ordered phases increases, thus improving significantly the spin-polarization. However, for samples annealed at higher temperatures, significant degradation in the cubic magneto-crystalline anisotropy is observed, which we attribute to the detection of manganese diffusion into the MgO substrate. This Mn diffusion is manifested in a reduction of the value of the TMR ratio, namely, the spin polarization. Additionally, the maximum TMR ratio measured here, approximately 65% at room-temperature, is limited because the semi-coherent interface of Co2MnSi with the MgO substrate terminates with a Mn-Si layer. (C) 2013 AIP Publishing LLC.

  121. Evaluation of interlayer exchange coupling in α-Fe(100)/Nd2Fe14B(001) Films 査読有り

    D. Ogawa, K. Koike, S. Mizukami, T. Miyazaki, M. Oogane, Y. Ando, H. Kato

    J. Korean Phys. Soc. 63 (2) 0-0 2013年7月

  122. Effect of Annealing Temperature on Structure and Magnetic Properties of L1(0)-FePd/CoFeB Bilayer 査読有り

    M. N. I. Khan, H. Naganuma, N. Inami, M. Oogane, Y. Ando

    IEEE TRANSACTIONS ON MAGNETICS 49 (7) 4409-4412 2013年7月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2013.2251612  

    ISSN:0018-9464

    eISSN:1941-0069

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    The effects of annealing temperature on the structural and magnetic properties of CoFeB/FePd bilayer were systematically investigated. A thin (0.5 nm) CoFeB layer was inserted between the FePd and MgO layers and then annealed at different temperatures. The magnetic anisotropy field increased with an increase in the annealing temperature owing to the enhancement of the interfacial perpendicular magnetic anisotropy (PMA) by crystallizing the thin CoFeB layer. The thermal annealing of the deposited layers promoted L1(0) ordering and reduced the surface roughness. It was found that a thinner FePd layer requires a higher annealing temperature in order to achieve PMA. After annealing at 350 degrees C, a PMA of 7.1 Merg/cc was obtained even for a thin FePd film with a thickness of 2.0 nm.

  123. Observation of Precessional Magnetization Dynamics in L1(0)-FePt Thin Films with Different L1(0) Order Parameter Values 査読有り

    Satoshi Iihama, Shigemi Mizukami, Nobuhito Inami, Takashi Hiratsuka, Gukcheon Kim, Hiroshi Naganuma, Mikihiko Oogane, Terunobu Miyazaki, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (7) 2013年7月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.52.073002  

    ISSN:0021-4922

    eISSN:1347-4065

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    Fast magnetization precession was observed in L1(0)-FePt thin films with different L1(0) order parameter values by all optical pump-probe technique. Precession frequency was varied widely for the films with different order parameter, which is due to large difference in perpendicular magnetic anisotropy. Gilbert damping constant (alpha) was estimated from relaxation time as apparent damping. Clear difference in alpha was not observed with different perpendicular magnetic anisotropy. (C) 2013 The Japan Society of Applied Physics

  124. The Enhancement of Magnetic Damping in Fe4N Films with Increasing Thickness 査読有り

    Shinji Isogami, Masakiyo Tsunoda, Mikihiko Oogane, Akimasa Sakuma, Migaku Takahashi

    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (7) 2013年7月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.7567/JJAP.52.073001  

    ISSN:0021-4922

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    The film thickness dependence of the magnetic damping coefficient (alpha) was investigated by measuring the ferromagnetic resonance (FMR) of Fe4N/NM (NM: Pt and Cu) bilayer films at room temperature. We observed that alpha in Fe4N/Pt films increased with increasing Fe4N film thickness. Moreover, the enhancement of alpha, which is represented by the difference in the alpha values of Fe4N/Pt and Fe4N/Cu films, also increased as the Fe4N film thickness increased. The behavior observed in the Fe4N system was the opposite of that observed for the conventional Ni-Fe system. We speculated two mechanisms occurring in Fe4N/Pt films, which are less magnetic and/or nonmagnetic impurities in the Fe4N films and enhancement of the coercive force (H-c) with increasing Fe4N film thickness. (C) 2013 The Japan Society of Applied Physics

  125. Fabrication of L1(0)-Ordered MnAl Films for Observation of Tunnel Magnetoresistance Effect 査読有り

    Haruaki Saruyama, Mikihiko Oogane, Yuta Kurimoto, Hiroshi Naganuma, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (6) 2013年6月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.52.063003  

    ISSN:0021-4922

    eISSN:1347-4065

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    We succeeded in fabricating L1(0)-ordered MnAl films with a high perpendicular magnetic anisotropy energy of 10(7) erg/cm(3) and a small average film roughness of 0.4nm by using a molten Mn-Al sputtering alloyed target and optimizing the substrate temperature. In addition, we investigated the tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs) with the prepared L1(0)-ordered MnAl electrode. The TMR effect was observed at RT in an MTJ with a very thin Co50Fe50 layer inserted into the MnAl electrode and MgO tunneling barrier interface. This is the first observation of the TMR effect in MTJs with an L1(0)-ordered MnAl electrode. (C) 2013 The Japan Society of Applied Physics

  126. Enhancement of Spin Pumping Efficiency in Fe4N/Pt Bilayer Films 査読有り

    Shinji Isogami, Masakiyo Tsunoda, Mikihiko Oogane, Akimasa Sakuma, Migaku Takahasi

    APPLIED PHYSICS EXPRESS 6 (6) 2013年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.7567/APEX.6.063004  

    ISSN:1882-0778

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    A DC electric voltage was generated on a Pt-capped Fe4N bilayer film (Fe4N/Pt) by inverse spin-Hall effect (ISHE) under ferromagnetic resonance (FMR) conditions at room temperature. Sign reversal of the electric voltage was observed with the application of an external DC field with opposite direction, and the magnitude of the voltage was proportional to the applied microwave power. The spin current was pumped out of the Fe4N film into the Pt capping film. The real part of the spin mixing conductance (g(r)(up down arrow)) was quantified for Fe4N/Pt and Ni78Fe22/Pt bilayer films to investigate the spin pumping efficiency at the interface. The g(r)(up down arrow) value was larger for the Fe4N/Pt film than for the Ni78Fe22/Pt film. Such a large g(r)(up down arrow) could reflect the large population of conduction electrons with minority spins in the Fe4N film compared with that with majority spins. (C) 2013 The Japan Society of Applied Physics

  127. Interface tailoring effect on magnetic properties and their utilization in MnGa-based perpendicular magnetic tunnel junctions 査読有り

    Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    PHYSICAL REVIEW B 87 (18) 2013年5月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.87.184426  

    ISSN:1098-0121

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    Insertion of a thin 3d ferromagnetic metal/alloy layer between the barrier layer and the perpendicularly magnetized ferromagnetic electrode is an effective method to enhance the magnetoresistance (MR) ratio in perpendicular magnetic tunnel junctions (p-MTJs). In the present paper we systematically studied the structural and magnetic properties as well as the spin-dependent transport in p-MTJs with a core structure MnGa/FM/MgO/CoFeB (FM = Fe, Co), with the MnGa being the L1(0) MnGa alloy (Mn57Ga43, Mn62Ga38) and the D0(22) MnGa alloy (Mn70Ga30). The insertion of the Fe and Co layers enhances the MR ratio significantly as well as the MnGa composition dependence of the MR ratio. In addition, opposite magnetic properties and MR(H) curves of MTJs with Fe and Co interlayers are observed, naturally suggesting the ferromagnetic and antiferromagnetic exchange coupling for MnGa/Fe(bcc) and MnGa/Co(bcc), respectively. By considering the exchange coupling between the FMand MnGa, we successfully simulated the MR(H) curves of the samples with Fe and Co interlayers based on a simple model. Furthermore, the interlayer effect on the transport properties are discussed based on the temperature dependence of the MR ratio by using the magnon excitation model modified with impurity-induced hopping. It shows that the FM interlayer restrains the impurity induced hopping and the magnon excitation; and furthermore, the Co is more effective in restraining the impurity diffusion and magnon excitation as compared to Fe.

  128. Magnetic tunnel junctions of perpendicularly magnetized L1(0)-MnGa/Fe/MgO/CoFe structures: Fe-layer-thickness dependences of magnetoresistance effect and tunnelling conductance spectra 査読有り

    T. Kubota, Q. L. Ma, S. Mizukami, X. M. Zhang, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 46 (15) 2013年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/46/15/155001  

    ISSN:0022-3727

    eISSN:1361-6463

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    The tunnel magnetoresistance (TMR) effect and the bias voltage dependence of tunnelling conductance spectra were measured in L1(0) Mn-Ga/Fe/MgO/CoFe magnetic tunnel junctions (MTJs). The TMR ratio and bias-voltage dependences on annealing conditions and Fe-layer thickness were investigated. The TMR ratio showed an increase subsequent to Fe-layer deposition under the optimum annealing condition, and a maximum value of 24% was achieved in an MTJ with a perpendicularly magnetized Fe layer of thickness of 1.1 nm at room temperature; this corresponded to a 57% TMR ratio in the case of completely antiparallel magnetization configuration. In the tunnelling conductance spectra, an anomalous dip, the so-called zero-bias anomaly, was observed for all the samples. The zero-bias anomaly is speculated to have appeared because of an increase in magnon excitation at the magnetic layer/barrier interfaces according to the model by Zhang et al (1997 Phys. Rev. Lett. 79 3744). In our experiments magnitude of the zero-bias anomaly depended on both the annealing condition and the Fe-layer thickness. We discuss our observation of the variation in the Curie temperature of the magnetic layer at the barrier layer interface depending on the the preparation conditions of the Fe insertion layer, which caused the change in the magnitude of the zero-bias anomaly.

  129. Detection of sub-nano-tesla magnetic field by integrated magnetic tunnel junctions with bottom synthetic antiferro-coupled free layer 査読有り

    Kosuke Fujiwara, Mikihiko Oogane, Takuo Nishikawa, Hiroshi Naganuma, Yasuo Ando

    Japanese Journal of Applied Physics 52 (4) 2013年4月

    DOI: 10.7567/JJAP.52.04CM07  

    ISSN:0021-4922 1347-4065

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    Arrays of 100 × 100 magnetic tunnel junctions (MTJs) connected in parallel and series were fabricated. A synthetic antiferro-coupled bottom free layer with a NiFe/Ru/CoFeB structure and MgO tunneling barrier were used to realize a high sensitivity, which is defined as TMR/2Hk, where, TMR is the tunneling magnetoresistance ratio and Hkis the magnetic anisotropy field of the free layer. To obtain a linear response of tunneling resistance against an applied external magnetic field, a double annealing process was carried out. From R-H curve measurements, the sensitivity of the 100 × 100 integrated MTJs was lower (8%/Oe) than that of a single MTJ (25%/Oe). However, a 1/30 decrease in noise power density was realized in the integrated MTJs. Consequently, a very small magnetic field of 0.29 nT was detected with the integrated MTJs. © 2013 The Japan Society of Applied Physics.

  130. Nonlinear Emission of Spin-Wave Caustics from an Edge Mode of a Microstructured Co2Mn0.6Fe0.4Si Waveguide 査読有り

    T. Sebastian, T. Braecher, P. Pirro, A. A. Serga, B. Hillebrands, T. Kubota, H. Naganuma, M. Oogane, Y. Ando

    PHYSICAL REVIEW LETTERS 110 (6) 2013年2月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.110.067201  

    ISSN:0031-9007

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    Magnetic Heusler materials with very low Gilbert damping are expected to show novel magnonic transport phenomena. We report nonlinear generation of higher harmonics leading to the emission of caustic spin-wave beams in a low-damping microstructured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher harmonic generation is a localized edge mode formed by the strongly inhomogeneous field distribution at the edges of the spin-wave waveguide. The radiation characteristics of the propagating caustic waves observed at twice and three times the excitation frequency are described by an analytical calculation based on the anisotropic dispersion of spin waves in a magnetic thin film. DOI: 10.1103/PhysRevLett.110.067201

  131. Tunnel magnetoresistance effect in tunnel junctions with Co2MnSi heusler alloy electrode and MgO barrier 査読有り

    Yasuo Ando, Sumito Tsunegi, Mikihiko Oogane, Hiroshi Naganuma, Koki Takanashi

    Spintronics: From Materials to Devices 355-366 2013年1月1日

    出版者・発行元:Springer Netherlands

    DOI: 10.1007/978-90-481-3832-6_17  

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    We demonstrated that a large TMR ratio of 753 % has been observed at 2 K in a MTJ using a Co2MnSi Heusler alloy electrode and a crystalline MgO tunnel barrier. At room temperature (RT), we also have observed a large TMR ratio of 217 %, which value at RT is much larger than that of MTJs using an amorphous Al-oxide tunnel barrier. However, the temperature dependence of the TMR ratio was still large. In order to improve the interface, we investigated the TMR effect in Co2MnSi/CoFeB(0-2 nm)/MgO/CoFe MTJs. TMR ratio was enhanced by inserting a thin CoFeB layer at the Co2MnSi/MgO interface. The MTJ with CoFeB thickness of 0.5 nm exhibited the highest TMR ratio. From the conductance-voltage measurements for the fabricated MTJs, we inferred that the highly spin polarized electron created in Co2MnSi can conserve the polarization through the 0.5 nm thick FeB layer.

  132. Evaluation of interlayer exchange coupling in alpha-Fe(100)/Nd2Fel4B(001) films 査読有り

    D. Ogawa, K. Koike, H. Kato, S. Mizukami, T. Miyazaki, M. Oogane, Y. Ando

    Journal of the Korean Physical Society 63 (3) 489-492 2013年

    DOI: 10.3938/jkps.63.489  

  133. Observation of a large spin-dependent transport length in organic Spin valves at room temperature 査読有り

    Xianmin Zhang, Shigemi Mizukami, Takahide Kubota, Qinli Ma, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    Nature Communications 4 2013年

    DOI: 10.1038/ncomms2423  

    ISSN:2041-1723

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    The integration of organic semiconductors and magnetism has been a fascinating topic for fundamental scientific research and future applications in electronics, because organic semiconductors are expected to possess a large spin-dependent transport length based on weak spin-orbit coupling and weak hyperfine interaction. However, to date, this length has typically been limited to several nanometres at room temperature, and a large length has only been observed at low temperatures. Here we report on a novel organic spin valve device using C 60 as the spacer layer. A magnetoresistance ratio of over 5% was observed at room temperature, which is one of the highest magnetoresistance ratios ever reported. Most importantly, a large spin-dependent transport length of approximately 110 nm was experimentally observed for the C 60 layer at room temperature. These results provide insights for further understanding spin transport in organic semiconductors and may strongly advance the development of spin-based organic devices. © 2013 Macmillan Publishers Limited. All rights reserved.

  134. Magnetoresistance enhancement in MnxGa 100 - X/MgO/CoFeB perpendicular magnetic tunnel junctions by using CoFeB interlayer 査読有り

    Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, M. Oogane, H. Naganuma, Y. Ando, T. Miyazaki

    IEEE Transactions on Magnetics 49 (7) 4339-4342 2013年

    DOI: 10.1109/TMAG.2013.2242861  

    ISSN:0018-9464

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    The magnetoresistance effects of the perpendicular magnetic tunnel junctions (p-MTJs) based on Mn-Ga ordered alloys are reported. By tuning the Mn-Ga composition, the MTJs based on L10 and D022 structured Mn-Ga alloys were achieved in the MTJ stack structure of Cr(40)/MnxGa100 - x(30)/Mg(0.4)/MgO(2.2)/CoFeB(1.2)/Ta(5)/ Ru(7) (nm). The values of magnetoresistance (MR) ratio at room temperature for different Mn-Ga composition are around 5%. In order to enhance the MR ratio, a thin CoFeB layer was introduced between the Mn-Ga and the MgO barrier. The MR effect shows a strong Mn-Ga composition dependent as CoFeB interlayer thickness increases. An MR ratio of 50% was obtained at room temperature when the CoFeB thickness is 1.5 nm for Mn62 Ga38 based MTJs. © 2013 IEEE.

  135. Magnetic Properties of Single Crystalline Co2MnAl Heusler Alloy Thin Films 査読有り

    Yilgin Resul, Sakuraba Yuya, Oogane Mikihiko, Ando Yasuo, Miyazaki Terunobu

    JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 25 (8) 2659-2663 2012年12月

    DOI: 10.1007/s10948-011-1238-x  

    ISSN:1557-1939

  136. EVALUATION OF EXCHANGE COUPLING IN Nd2Fe14B/α-Fe INTERFACES

    D. Ogawa, K. Koike, S. Mizukami, T. Miyazaki, M. Oogane, Y. Ando, H. Kato

    Proceedings on 21st Workshop on Rare-Earth Permanent Magnets and their Applications (REPM'12) 2012年9月2日

  137. Enhancement of magnetoresistance using CoFe/Ru/CoFe synthetic ferrimagnetic pinned layer in BiFeO3 based spin-valves 査読有り

    Hiroshi Naganuma, In-Tae Bae, Takamichi Miyazaki, Miho Kubota, Nobuhito Inami, Yuki Kawada, Mikihiko Oogane, Shigemi Mizukami, X. F. Han, Yasuo Ando

    APPLIED PHYSICS LETTERS 101 (7) 2012年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4745504  

    ISSN:0003-6951

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    SrTiO3 (100) sub/BiFeO3/CoFe/Ru/CoFe/Cu/CoFe/Ta structure was prepared by a combination of chemical solution deposition and sputtering method, and followed by a systematical investigation for the structural, magnetic and magnetoresistance properties at room temperature (RT) as a function of CoFe and Ru thicknesses. It was revealed that introduction of synthetic CoFe/Ru/CoFe as a pinning layer increased the giant magentoresistance (MR) ratio to 8.3% at RT. This enhancement of MR ratio might be attributed to (i) the increase of pinning field, and (ii) suppression of the influence of the surface roughness of BiFeO3 by inserting the synthetic CoFe/Ru/CoFe layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745504]

  138. Magnetoresistance effect in L1(0)-MnGa/MgO/CoFeB perpendicular magnetic tunnel junctions with Co interlayer 査読有り

    Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    APPLIED PHYSICS LETTERS 101 (3) 2012年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4737000  

    ISSN:0003-6951

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    The fully perpendicular magnetic tunnel junctions (p-MTJs) based on L1(0)-MnGa and thin CoFeB electrodes with MgO barrier were reported in this letter. A thin Co layer was introduced between the MnGa layer and the MgO barrier layer to investigate interfacial effect on the device's magnetic and transport properties. The magnetoresistance ratio improved significantly due to the Co insertion, and reached 40% at room temperature (80% at 5 K) when the Co thickness was 1.5 nm. Moreover, the junctions with Co interlayer exhibited four low-resistance states in one full cycle rather than two in normal MTJs. The physical origin was discussed by considering the coupling between MnGa and Co layers. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737000]

  139. Nd2Fe14B/α-Fe界面における交換結合の評価

    小川大介, 小池邦博, 水上成美, 大兼幹彦, 安藤康夫, 宮崎孝道, 加藤宏朗

    信学技報 2012年6月14日

  140. Annealing Temperature and Co Layer Thickness Dependence of Magnetoresistance Effect for -MnGa/Co/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions 査読有り

    Q. L. Ma, Takahide Kubota, Shigemi Mizukami, X. M. Zhang, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    IEEE Transactions on Magnetics 48 2808-2811 2012年4月16日

    DOI: 10.1109/TMAG.2012.2196420  

  141. Fabrication of L1(0)-MnAl perpendicularly magnetized thin films for perpendicular magnetic tunnel junctions 査読有り

    Masaki Hosoda, Mikihiko Oogane, Miho Kubota, Takahide Kubota, Haruaki Saruyama, Satoshi Iihama, Hiroshi Naganuma, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 111 (7) 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3676428  

    ISSN:0021-8979

    eISSN:1089-7550

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    Structural and magnetic properties of MnAl thin films with different composition, growth temperature, and post-annealing temperature were investigated. The optimum condition for fabrication of L1(0)-MnAl perpendicularly magnetized thin film deposited on Cr-buffered MgO single crystal substrate was revealed. The results of x ray diffraction indicated that the MnAl films annealed at proper temperature had a (001)-orientation and L1(0)-ordered structure. The L1(0)-ordered films were perpendicularly magnetized and had a large perpendicular anisotropy. In addition, low surface roughness was achieved. For the optimized fabrication condition, the saturation magnetization M-s of 600 emu/cm(3) and perpendicular magnetic anisotropy K-u of 1.0 x 10(7) erg/cm(3) was obtained using the Mn48Al52 target at deposition temperature of 200 degrees C and post-annealing temperature of 450 degrees C. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676428]

  142. Dependence of spin-transfer switching characteristics in magnetic tunnel junctions with synthetic free layers on coupling strength 査読有り

    Masayuki Nishimura, Mikihiko Oogane, Hiroshi Naganuma, Nobuhito Inami, Tadashi Morita, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 111 (7) 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3672240  

    ISSN:0021-8979

    eISSN:1089-7550

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    Dependence of spin-transfer switching characteristics on the interlayer exchange coupling strength in the MTJs with synthetic free layers of Co90Fe10/Ru/Co40Fe40B20 with strong coupling strength was investigated. In the MTJ with the relatively weakly coupled synthetic ferrimagnetic free layer, larger thermal stability (Delta(0)) and lower intrinsic critical current density (J(c0)) than those of the MTJ with the single free layer were observed. Meanwhile, in the MTJs with the strongly coupled synthetic ferri- or ferromagnetic free layers, very large Delta(0) and high J(c0) were observed probably due to high effective magnetic energy barrier. It was found that the MTJ with the relatively weakly coupled synthetic ferrimagnetic free layer is suitable for the STTRAM application. (C) 2012 American Institute of Physics. [doi:10.1063/1.3672240]

  143. Promotion of L1(0) ordering of FePd films with amorphous CoFeB thin interlayer 査読有り

    M. N. I. Khan, N. Inami, H. Naganuma, Y. Ohdaira, M. Oogane, Y. Ando

    JOURNAL OF APPLIED PHYSICS 111 (7) 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3673409  

    ISSN:0021-8979

    eISSN:1089-7550

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    The L1(0)-ordered FePd thin films were prepared using an ultrahigh vacuum magnetron sputtering system on MgO(001) substrates at 300 degrees C. The crystallographic and magnetic properties and the surface morphology of films with and without a very thin amorphous CoFeB intermediate layer inserted between the FePd and the MgO layers were systematically investigated as a function of the thickness of the FePd layer. The perpendicular anisotropy of the samples was increased by inserting the thin CoFeB as an intermediate layer below the FePd with a thickness of 4.0 nm. The reason for the enhancement by inserting the amorphous CoFeB layer is attributed to: (i) the promotion of the L1(0) ordering of the FePd due to the reduction of the lattice mismatch between the MgO and FePd, and (ii) the fact that thin CoFeB has a perpendicular anisotropy at the interface of the MgO, which superposed the perpendicular anisotropy of the L1(0)-FePd. (C) 2012 American Institute of Physics. [doi:10.1063/1.3673409]

  144. Large change of perpendicular magnetic anisotropy in Cobalt ultrathin film induced by varying capping layers 査読有り

    Xianmin Zhang, Shigemi Mizukami, Takahide Kubota, Qinli Ma, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 111 (7) 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3676240  

    ISSN:0021-8979

    eISSN:1089-7550

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    The magnetic films of Co with Si/SiO2/Pt/Co/molecule structure were fabricated and their structural properties and magnetic anisotropy were investigated by varying both Co (0.5-1.8 nm) thickness and molecular capping layers of 5,6,11,12-tetraphenylnaphthacene (rubrene) and copper phthalocyanine (CuPc), respectively. The crystal structures were characterized using x-ray diffraction (XRD) and the magnetization curves were measured using vibrating sample magnetometer with an applied field both in parallel and perpendicular to a film plane. It was found that the thickness of Co for the maximum perpendicular magnetic anisotropy (PMA) is around 0.7 nm for both group films. However, the estimated effective magnetic anisotropy energy for Co was 2.9 +/- 0.3 x 10(6) erg/cc for rubrene-capped sample, which was smaller than the value of 4.9 +/- 0.4 x 10(6) erg/cc for CuPc-capped sample. The XRD patterns showed the crystal structure of rubrene layer was of amorphous structure and CuPc layer was polycrystalline. The different interface effects of Co/CuPc and Co/rubrene were discussed to analyze the change of PMA. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676240]

  145. Fabrication of magnetic tunnel junctions with a bottom synthetic antiferro-coupled free layers for high sensitive magnetic field sensor devices 査読有り

    Kosuke Fujiwara, Mikihiko Oogane, Saeko Yokota, Takuo Nishikawa, Hiroshi Naganuma, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 111 (7) 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3677266  

    ISSN:0021-8979

    eISSN:1089-7550

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    Magnetic tunnel junctions with a Ni80Fe20/Ru/Co40Fe40B20 synthetic antiferro-coupled bottom free layer and an MgO barrier layer have been fabricated. Double annealing process was carried out in order to obtain linearity against magnetic field with hysteresis-free resistance response. The effect of the annealing temperature and NiFe thickness in the free layer on the magnetic field sensor performance was investigated. We have observed a very high sensitivity of 25.3%/Oe while keeping linearity. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677266]

  146. Dependence of Tunnel Magnetoresistance Effect on Fe Thickness of Perpendicularly Magnetized L1(0)-Mn62Ga38/Fe/MgO/CoFe Junctions 査読有り

    Takahide Kubota, Qinli Ma, Shigemi Mizukami, Xianmin Zhang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS EXPRESS 5 (4) 2012年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.5.043003  

    ISSN:1882-0778

    eISSN:1882-0786

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    The tunnel magnetoresistance (TMR) ratio in a magnetic tunnel junction (MTJ) with an L1(0)-Mn62Ga38/Fe/MgO/CoFe structure was considerably improved by Fe layer insertion. A maximum TMR ratio of 24% was observed in an MTJ with a Fe thickness of 1.1nm at room temperature, which corresponded to a 57% TMR ratio in the case of a complete antiparallel magnetization configuration. Fe layer thickness dependences of the magnetization curve and TMR effect were also investigated. It was revealed that the magnetization of Fe on 30-nm-thick MnGa could be fixed in a perpendicular direction when the thickness of the Fe was below 2.0 nm. (C) 2012 The Japan Society of Applied Physics

  147. Low-damping spin-wave propagation in a micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide 査読有り

    T. Sebastian, Y. Ohdaira, T. Kubota, P. Pirro, T. Braecher, K. Vogt, A. A. Serga, H. Naganuma, M. Oogane, Y. Ando, B. Hillebrands

    APPLIED PHYSICS LETTERS 100 (11) 2012年3月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3693391  

    ISSN:0003-6951

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    We report on the investigation of spin-wave propagation in a micro-structured Co2Mn0.6Fe0.4Si (CMFS) Heusler waveguide. The reduced magnetic losses of this compound compared to the commonly used Ni81Fe19, allow for the observation of spin-wave propagation over distances as high as 75 mu m via Brillouin light scattering (BLS) microscopy. In the linear regime, a maximum decay length of 16.7 mu m of the spin-wave amplitude was found. The coherence length of the observed spin-wave modes was estimated to be at least 16 mu m via phase-resolved BLS techniques. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693391]

  148. Spin-RAM for Normally-Off Computer 査読有り

    K.Ando, K.Yakushiji, H.Kubota, A.Fukushima, S.Yuasa, T.Kai, T.Kishi, N.Shimomura, H.Aikawa, M.Yoshikawa, T.Nagase, K.Nishiyama, E.Kitagawa, T.Daibou, M.Amano, S.Takahashi, M.Nakayama, S.Ikegawa, M.Nagamine, J.Ozeki, D.Watanabe, H.Yoda, T.Nozaki, Y.Suzuki, M.Oogane, S.Mizukami, Y.Ando, T.Miyazaki, Y.Nakatani

    Conference Publications NVMTSプロシーディング 1-6 2012年1月

    DOI: 10.1109/NVMTS.2011.6137104  

  149. α-Fe(100)/Nd2Fe14B(001)界面における交換結合の評価

    小川 大介, 小池 邦博, 水上 成美, 大兼 幹彦, 安藤 康夫, 宮崎 孝道, 加藤 宏朗

    Journal of the Magnetics Society of Japan 36 (1) 5-12 2012年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.1201R001  

    ISSN:1882-2924

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    Magnetic bilayer films with an interface of α-Fe(100) and Nd<sub>2</sub>Fe<sub>14</sub>B(001) planes were fabricated in order to evaluate the exchange-coupling constant, which was recently reported to depend on the Miller indices of the interface planes. The epitaxial growth of both α-Fe and Nd<sub>2</sub>Fe<sub>14</sub>B layers was confirmed with the epitaxial relation of MgO(100)[100] || α-Fe(100)[110] || Nd<sub>2</sub>Fe<sub>14</sub>B(001) [110], according to the X-ray pole-figure measurements. FMR experiments on this film were performed by using a Q-band microwave apparatus. We observed a significant shift of α-Fe resonance field from <i>H</i><sub>r</sub> = 5.24 kOe to <i>H</i><sub>r</sub> = 4.41 kOe in a bilayer film sputtered at T<sub>S</sub><sup>NFB</sup> = 650°C compared to a reference film without an Nd<sub>2</sub>Fe<sub>14</sub>B layer. This lower shift suggests the existence of an internal field due to the positive exchange coupling between α-Fe and Nd<sub>2</sub>Fe<sub>14</sub>B phases. The magnitude of the exchange-coupling constant was estimated to be in the range between 6.5 and 11 erg/cm<sup>2</sup> for the bilayer film sputtered at T<sub>S</sub><sup>NFB</sup> = 650°C.

  150. Composition dependence of magnetic properties in perpendicularly magnetized epitaxial thin films of Mn-Ga alloys 査読有り

    S. Mizukami, T. Kubota, F. Wu, X. Zhang, T. Miyazaki, H. Naganuma, M. Oogane, A. Sakuma, Y. Ando

    PHYSICAL REVIEW B 85 (1) 2012年1月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.85.014416  

    ISSN:1098-0121

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    Mn-Ga binary alloys show strong magnetism and large uniaxial magnetic anisotropy even though these alloys do not contain any noble, rare-earth metals or magnetic elements. We investigate the composition dependence of saturation magnetization M(S) and uniaxial magnetic anisotropy K(u) in epitaxial films of M(n-x)Ga(1-x) alloys (x similar to 0.5-0.75) grown by magnetron sputtering. The M(S) values decrease linearly from approximately 600 to 200 emu/cm(3) with increasing x, whereas the K(u) values decrease slightly from approximately 15 to 10 Merg/cm(3) with increasing x. These trends are distinct from those for known tetragonal hard magnets obtained in a limited composition range in Mn-Al and Fe-Pt binary alloys. These data are analyzed using a localized magnetic moment model.

  151. The magnetic and structural properties of Co2MnSi Heusler alloy thin films on the orientation of Ge substrate 査読有り

    M. A. I. Nahid, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    Phys. Status Solidi A 208 675-378 2011年12月6日

    DOI: 10.1002/pssa.201026569  

  152. Composition dependence of magnetoresistance effect and its annealing endurance in tunnel junctions having Mn-Ga electrode with high perpendicular magnetic anisotropy 査読有り

    Takahide Kubota, Masaaki Araidai, Shigemi Mizukami, Xianmin Zhang, Qinli Ma, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Masaru Tsukada, Terunobu Miyazaki

    APPLIED PHYSICS LETTERS 99 (19) 2011年11月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3659484  

    ISSN:0003-6951

    eISSN:1077-3118

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    The composition dependence of the tunnel magnetoresistance (TMR) effect in Mn-Ga/MgO/CoFe magnetic tunnel junctions (MTJs) for Mn54Ga46, Mn62Ga38, and Mn71Ga29 (at. %) electrodes was investigated. An MTJ with a Mn62Ga38 electrode showed a maximum TMR ratio of 23% at 10 K and high annealing endurance up to 375 degrees C. The bias voltage dependence of the TMR ratio was distinct among MTJs with different Mn-Ga compositions. Here, we discuss this dependence on the basis of the difference in the Delta(1) band dispersions for Mn-Ga alloys calculated by first principles. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3659484]

  153. Large Magnetoresistance Effect in Epitaxial Co2Fe0.4Mn0.6Si/Ag/Co2Fe0.4Mn0.6Si Devices 査読有り

    Jo Sato, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    APPLIED PHYSICS EXPRESS 4 (11) 2011年11月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.4.113005  

    ISSN:1882-0778

    eISSN:1882-0786

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    Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with a Co2Fe0.4Mn0.6Si/Ag/Co2Fe0.4Mn0.6Si structure were fabricated. The bottom and top Co2Fe0.4Mn0.6Si layers had good crystallinity and an L2(1)-ordered structure. In addition, we found from scanning transmission electron microscopy (STEM) measurements that both Co2Fe0.4Mn0.6Si/Ag and Ag/Co2Fe0.4Mn0.6Si interfaces were very flat and sharp. The magnetoresistance (MR) ratio at room temperature was 74.8%, the largest to date for CPP-GMR devices. CPP-GMR devices with Co2Fe0.4Mn0.6Si electrodes would be very useful for the next generation of hard disk drive (HDD) read heads. (C) 2011 The Japan Society of Applied Physics

  154. Interface effects on perpendicular magnetic anisotropy for molecular-capped cobalt ultrathin films 査読有り

    Xianmin Zhang, Shigemi Mizukami, Takahide Kubota, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS LETTERS 99 (16) 2011年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3651766  

    ISSN:0003-6951

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    The perpendicular magnetic anisotropy (PMA) of cobalt (0.5-1.8 nm) films capped separately by pentacene (Pc), fullerene (C(60)), and 8-hydroxyquinoline-aluminum (Alq(3)) are investigated. For all three series, the thickness of Co is around 0.7 nm for maximum out-of-plane coercivity. It is found that the coercivity of C(60)-capped films is nearly equal to that for Alq(3)-capped samples, although both are smaller than for Pc-capped films. The different interface effects of Co/molecules are discussed to explain this observation. This work highlights the PMA of ferromagnetic metal, which can be markedly infected depending on the nature of organic molecule. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651766]

  155. Influence of Pt Doping on Gilbert Damping in Permalloy Films and Comparison with the Perpendicularly Magnetized Alloy Films 査読有り

    Shigemi Mizukami, Takahide Kubota, Xianmin Zhang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS 50 (10) 2011年10月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.50.103003  

    ISSN:0021-4922

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    Effects of Pt doping on magnetic properties and Gilbert damping are investigated for Ni80Fe20 permalloy films to compare with damping in alloy films containing Pt with a large perpendicular anisotropy. Gilbert damping constant alpha and g-factor g for (Ni80Fe20)(100-x)Pt-x (x = 0-34 at. %) are evaluated from out-of-plane angular variations of ferromagnetic resonance (FMR) linewidth and resonance field with an analysis based on the Landau-Lifshitz-Gilbert equation. Data of angular dependence of the FMR linewidth are fitted reasonably well by a theoretical model without having to take into account any extrinsic influences on linewidth, thereby allowing us to determine precise values of alpha. The alpha values show variation with increasing Pt concentration rising by similar to 0:06 at a Pt concentration of 34 at. %, which is very close to those in perpendicularly magnetized CoCrPt and FePt film reported recently. Nevertheless, Gilbert damping rate G for the Pt doped permalloy films is smaller than those in CoCrPt and FePt films. These experimental results are discussed with a spin-orbit torque theory. (C) 2011 The Japan Society of Applied Physics

  156. Time-Resolved Kerr Effect in Very Thin Films of CoCrPt Alloys 査読有り

    Shigemi Mizukami, Daisuke Watanabe, Takahide Kubota, X. Zhang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, T. Miyazaki

    IEEE Transaction on Magnetics 47 (10) 3897-38900 2011年9月23日

    DOI: 10.1109/TMAG.2011.2154357  

  157. Spin Transport in Co/Al2O3 Alq3 Co Organic Spin Valve 査読有り

    Xianmin Zhang, Shigemi Mizukami, Takahide Kubota???, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    IEEE TRANSACTIONS ON MAGNETICS 47 (10) 2649-2651 2011年9月

  158. Spin transistor using magnetic tunnel junctions with half-metallic Co2MnSi Heusler alloy electrodes 査読有り

    Y. Ohdaira, M. Oogane, H. Naganuma, Y. Ando

    APPLIED PHYSICS LETTERS 99 (13) 2011年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3645637  

    ISSN:0003-6951

    eISSN:1077-3118

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    We fabricated a spin transistor structure that consisted of two magnetic tunnel junctions with half-metallic Co2MnSi electrodes. Transient responses were observed by applying pulsing gate voltage. Output currents were controlled by both the source-drain and gate voltage and magnetic configuration of the Co2MnSi. The drain current increased around 3000 times at a source-drain voltage of 0.01 V and anti-parallel magnetic configuration, when a gate voltage of 1 V peak-to-peak was applied. In addition, the maximum magnetocurrent ratios were 215% at 6 K. Expected operation properties are observed in our proposed spin transistor. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3645637]

  159. Tunnel magnetoresistance effect and magnetic damping in half-metallic Heusler alloys 招待有り 査読有り

    M. Oogane, S. Mizukami

    PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 369 (1948) 3037-3053 2011年8月

    出版者・発行元:ROYAL SOC

    DOI: 10.1098/rsta.2011.0011  

    ISSN:1364-503X

    eISSN:1471-2962

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    Some full-Heusler alloys, such as Co2MnSi and Co2MnGe, are expected to be half-metallic ferromagnetic material, which has complete spin polarization. They are the most promising materials for realizing half-metallicity at room temperature owing to their high Curie temperature. We demonstrate a huge tunnel magnetoresistance effect in a magnetic tunnel junction using a Co2MnSi Heusler alloy electrode. This result proves high spin polarization of the Heusler alloy. We also demonstrate a small magnetic damping constant in Co2FeAl epitaxial film. The very high spin polarization and small magnetic constant of Heusler alloys will be a great advantage for future spintronic device applications.

  160. Fabrication of MgO-based magnetic tunnel junctions for subnanosecond spin transfer switching 査読有り

    Tatsuya Aoki, Yasuo Ando, Mikihiko Oogane, Hiroshi Naganuma

    Journal of Physics: conference serise 266 012086 2011年7月

    DOI: 10.1088/1742-6596/266/1/012086  

  161. Effect of metallic Mg insertion on the magnetoresistance effect in MgO-based tunnel junctions using D022-Mn3-δGa perpendicularly magnetized spin polarizer 査読有り

    Takahide Kubota, Shigemi Mizukami, Daisuke Watanabe, Feng Wu, Xianmin Zhang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    J. Appl. Phys. 110, 013915 (2011) 110 (1) 2011年7月

    出版者・発行元:None

    DOI: 10.1063/1.3603034  

    ISSN:0021-8979

  162. Fabrication of Multiferroic Co-Substituted BiFeO3 Epitaxial Films on SrTiO3 (100) Substrates by Radio Frequency Magnetron Sputtering 査読有り

    Husne Ara Begum, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    Materials 4 1087-1095 2011年6月9日

    DOI: 10.3390/ma4061087  

  163. The effect of film and interface structure on the transport properties of Heusler based current-perpendicular-to-plane spin valves 査読有り

    V. K. Lazarov, K. Yoshida, J. Sato, P. J. Hasnip, M. Oogane, A. Hirohata, Y. Ando

    APPLIED PHYSICS LETTERS 98 (24) 2011年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3600792  

    ISSN:0003-6951

    eISSN:1077-3118

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    We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L2(1) but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L2(1). The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600792]

  164. Magnetoresistance Effect in Tunnel Junctions with Perpendicularly Magnetized D0(22)-Mn3-delta Ga Electrode and MgO Barrier 査読有り

    Takahide Kubota, Yoshio Miura, Daisuke Watanabe, Shigemi Mizukami, Feng Wu, Hiroshi Naganuma, Xianmin Zhang, Mikihiko Oogane, Masafumi Shirai, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS EXPRESS 4 (4) 2011年4月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.4.043002  

    ISSN:1882-0778

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    The tunnel magnetoresistance (TMR) effect with a perpendicularly magnetized D0(22)-Mn3-delta Ga (delta = 0.6) electrode was investigated in epitaxially grown D0(22)-Mn3-delta Ga (30)/Mg (d(Mg))/MgO (2)/CoFe (2.5) (nm) magnetic tunnel junctions (MTJs). The maximum TMR ratio of 9.8% (22.1%) was achieved at 300 K (10 K) with d(Mg) = 0: 4 nm. The bias voltage dependence of differential conductance spectra suggests the existence of a coherent tunneling process in the MTJs. First principles calculations of band dispersion relations and tunneling transmittance in a Mn3Ga/MgO/Mn3Ga structure were also performed. The results revealed the existence of Delta(1)-bands in Mn3Ga and demonstrated the possibility of a coherent tunneling process existing in the MTJ. (C) 2011 The Japan Society of Applied Physics

  165. Exchange biases of Co, Py, Co40Fe40B20, Co75Fe25, and Co50Fe50 on epitaxial BiFeO3 films prepared by chemical solution deposition 査読有り

    Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 109 (7) 2011年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3563061  

    ISSN:0021-8979

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    Multiferroic BiFeO3 epitaxial films were fabricated on SrTiO3 (100) substrates by a chemical solution deposition method. Magnetic layers of Co, Py, Co40Fe40B20, Co75Fe25, and Co50Fe50 were then deposited by sputtering under a magnetic field. Despite employing a chemical process, a clear exchange bias was observed for all the magnetic materials. The temperature dependence of Hex was evaluated for a Co50Fe50/BiFeO3 bilayer having a relatively large Hex and high squareness. The Hex of Co50Fe50/BiFeO3 bilayer increased between 10 to 250 K. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3563061]

  166. Long-Lived Ultrafast Spin Precession in Manganese Alloys Films with a Large Perpendicular Magnetic Anisotropy 査読有り

    S. Mizukami, F. Wu, A. Sakuma, J. Walowski, D. Watanabe, T. Kubota, X. Zhang, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    PHYSICAL REVIEW LETTERS 106 (11) 2011年3月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.106.117201  

    ISSN:0031-9007

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    Spin precession with frequencies up to 280 GHz is observed in Mn(3-delta)Ga alloy films with a perpendicular magnetic anisotropy constant K(u) similar to 15 Merg/cm(3). The damping constant alpha, characterizing macroscopic spin relaxation and being a key factor in spin-transfer-torque systems, is not larger than 0.008 (0.015) for the delta = 1.46 (0.88) film. Those are about one-tenth of alpha values for known materials with large K(u). First-principles calculations well describe both low alpha and large K(u) for these alloys.

  167. The effect of inserting thin Co2MnAl layer into the Co2MnSi/MgO interface on tunnel magnetoresistance effect 査読有り

    E. Ozawa, S. Tsunegi, M. Oogane, H. Naganuma, Y. Ando

    Journal ofPhysics:ConferenceSeries 266 012104-1-012104-4 2011年1月28日

    DOI: 10.1088/1742-6596/266/1/012104  

  168. Magnetoresistance Effect in Co2MnSi/semimetallic-Fe2VAl/CoFe Junctions 査読有り

    T Kubota, M Oogane, S Mizukami, H Naganuma, Y Ando, T Miyazaki

    Journal ofPhysics:ConferenceSeries 266 012096-1-012096-5 2011年1月28日

    DOI: 10.1088/1742-6596/266/1/012096  

  169. Influence of composition on structure and magnetic properties of epitaxial Mn-Ga films 査読有り

    F Wu, S Mizukami, D Watanabe, H Naganuma, M Oogane, Y Ando, T Miyazaki

    Journal of Physics: Conference Series 266 012112-1-012112-5 2011年1月28日

    DOI: 10.1088/1742-6596/266/1/012112  

  170. Retraction: ‘‘Large Tunnel Magnetoresistance of 1056% at Room Temperature in MgO Based Double Barrier Magnetic Tunnel Junction’’ [Appl. Phys. Express 2 (2009) 083002] 査読有り

    Hiroshi Naganuma, Lixian Jiang, Mikihiko Oogane, Yasuo Ando

    Applied Physics Express 4 (1) 019201-019201 2011年1月

    出版者・発行元:None

    DOI: 10.1143/APEX.4.019201  

    ISSN:1882-0778

  171. Laser-induced fast magnetization precession and Gilbert damping for CoCrPt alloy thin films with perpendicular magnetic anisotropy 査読有り

    Shigemi Mizukami, Daisuke Watanabe, Takahide Kubota, Xianmin Zhang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    Applied physics express 3 123001-1-123001-3 2011年

  172. Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy 査読有り

    Shigemi Mizukami, Xianmin Zhang, Takahide Kubota, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS EXPRESS 4 (1) 2011年1月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.4.013005  

    ISSN:1882-0778

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    Gilbert damping is reported in perpendicularly magnetized Ni/Co multilayer films with Pt buffer and capping layers, and investigated through the time-resolved magneto-optical Kerr effect under various applied magnetic field strengths and directions. Both damping constant alpha and perpendicular magnetic anisotropy energy K(u) depend strongly on layer thickness and bilayer periodicity, and rise to approximately 0.08 and 8 Merg/cm(3), respectively. The Gilbert damping rate depends linearly on inverse multilayer thickness, indicating that large damping in the Ni/Co multilayers stems from its interfaces in contact with the Pt layers. (C) 2011 The Japan Society of Applied Physics

  173. Fabrication of Magnetic Tunnel Junctions with a Synthetic Ferrimagnetic Free Layer for Magnetic Field Sensor Applications 査読有り

    Kousuke Fujiwara, Mikihiko Oogane, Futoyoshi Kou, Daisuke Watanabe, Hiroshi Naganuma, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 50 (1) 2011年1月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.50.013001  

    ISSN:0021-4922

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    Magnetic tunnel junctions (MTJs) with a CoFeB/Ru/Ni80Fe20 synthetic ferrimagnetic free layer and an MgO barrier layer were fabricated. The effect of the shape and thickness of the free layer on the magnetic field sensor characteristics was systematically investigated. We achieved a high sensitivity of 4.8%/Oe in the MTJ with a 70-nm-thick Ni80Fe20 layer and an aspect ratio of 1.0. Here, sensitivity is defined as TMR/(2H(k)), where TMR is tunnel magnetoresistance ratio in the MTJ and H-k is a magnetic anisotropy field of the free layer. Furthermore, we successfully increased the detection field range up to 230 Oe while keeping high sensitivity and linearity. (c) 2011 The Japan Society of Applied Physics

  174. Fast magnetization precession observed in L1(0)-FePt epitaxial thin film 査読有り

    S. Mizukami, S. Iihama, N. Inami, T. Hiratsuka, G. Kim, H. Naganuma, M. Oogane, Y. Ando

    APPLIED PHYSICS LETTERS 98 (5) 2011年1月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3549704  

    ISSN:0003-6951

    eISSN:1077-3118

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    Fast magnetization precession is observed in L1(0)-FePt alloy epitaxial thin films excited and detected by all-optical means. The precession frequency varies from 45 to 65 GHz depending on the applied magnetic field strength and direction, which can be explained by a uniform precession model taking account of first- and second-order uniaxial magnetic anisotropy. The lowest effective Gilbert damping constant has a minimum value of 0.055, which is about half that in Co/Pt multilayers and is comparable to Ni/Co multilayers with perpendicular magnetic anisotropy. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549704]

  175. Band-Structure-Dependent Demagnetization in the Heusler Alloy Co2Mn1-xFexSi 査読有り

    Daniel Steil, Sabine Alebrand, Tobias Roth, Michael Krauss, Takahide Kubota, Mikihiko Oogane, Yasuo Ando, Hans Christian Schneider, Martin Aeschlimann, Mirko Cinchetti

    PHYSICAL REVIEW LETTERS 105 (21) 2010年11月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.105.217202  

    ISSN:0031-9007

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    We investigate the ultrafast demagnetization for two Heusler alloys (Co2Mn1-xFexSi) with a different lineup of the minority band gap and the Fermi level. Even though electronic spin-flip transitions are partially blocked by the band gap in one compound, the respective magnetization dynamics, as measured by the time-resolved Kerr effect, are remarkably similar. Based on a dynamical model that includes momentum and spin-dependent carrier scattering, we show that the magnetization dynamics are dominated by hole spin-flip processes, which are not influenced by the gap.

  176. Ferromagnetic resonance investigation of exchange coupling in Nd2Fe14B/α-Fe interfaces

    D. Ogawa, K. Koike, T. Miyazaki, S. Mizukami, T. Akiya, M. Oogane, Y. Ando, H. Kato

    Proc. on the 21th International Workshop on Rare-earth Permanent Magnets and their Applications 2010年8月28日

  177. Gilbert magnetic damping constant of epitaxially grown Co-based Heusler alloy thin films 査読有り

    M. Oogane, T. Kubota, Y. Kota, S. Mizukami, H. Naganuma, A. Sakuma, Y. Ando

    APPLIED PHYSICS LETTERS 96 (25) 2010年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3456378  

    ISSN:0003-6951

    eISSN:1077-3118

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    The magnetic damping constant in a series of Co2MnAlxSi1-x and Co2FexMn1-xSi Heusler alloy epitaxial films were systematically investigated by using ferromagnetic resonance technique. The determined magnetic damping constant is roughly proportional to the density of states at the Fermi energy of the first principle calculation. The result is consistent with the theoretical prediction when taking spin-orbit interaction into account. The small Gilbert damping constant for the fabricated films other than the Co2FexMn1-xSi film with x&gt;0.6 can be originated in the half-metallic electronic structure of Heusler alloys. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456378]

  178. Structural and Magnetic Properties of Perpendicular Magnetized Mn2.5Ga Epitaxial Films 査読有り

    F. Wu, S. Mizukami, D. Watanabe, E. P. Sajitha, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    IEEE TRANSACTIONS ON MAGNETICS 46 (6) 1863-1865 2010年6月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2010.2045108  

    ISSN:0018-9464

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    The influence of annealing temperature and film thickness on structural and magnetic properties of Mn2.5Ga films were investigated in this work. The annealing temperature of 400 degrees C was found to be the optimum condition to obtain the films with high perpendicular magnetic anisotropy (PMA) (K-u(eff) = 7.8 x 10(6) erg/cm(3)) and smooth surface (R-a approximate to 0.15 nm). The PMA property was maintained in the 5 nm thick film, and deterioration of the PMA properties with decreasing film thickness can be ascribed to the tensile strain existed in the thin Mn2.5Ga films.

  179. Magnetization Dynamics in CoFeB Buffered Perpendicularly Magnetized Co/Pd Multilayer 査読有り

    E. P. Sajitha, Jakob Walowski, D. Watanabe, S. Mizukami, Feng Wu, Hiroshi Naganuma, Mikihito Oogane, Yasuo Ando, T. Miyazaki

    IEEE TRANSACTIONS ON MAGNETICS 46 (6) 2056-2059 2010年6月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2009.2038929  

    ISSN:0018-9464

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    The magnetic properties of CoFeB buffered [Co(0.3 nm)/Pd(x nm)](6) multilayer films have been investigated. It is found that the magnetic properties of the multilayer depended on the Pd thickness and for thickness below 0.5 nm no perperdicular anisotropy is observed. Magnetization dynamics in perpendicularly magnetized CoFeB-[Co/Pd] multilayer films are investigated using time-resolved magneto-optical Kerr effect (TRMOKE). The variation of precession frequency with external magnetic field for different palladium thickness is quantitatively understood using the macrospin approximation of the Landau-Lifshitz-Gilbert equation of motion. The Gilbert damping constant alpha, in the range 0.04-0.1, varying with the palladium thickness is reported. The observed alpha value is comparable to the damping coefficient of bulk Ni, and much lower than the reported values for perpendicularly magnetized films. The CoFeB buffer layer with in-plane anisotropy appears to significantly affect the precession frequency and thus the damping constant of the films.

  180. The Effect of Doping Concentration of Si on the Nature of Barrier of Co2MnSi/MgO/n-Si Junctions 査読有り

    M. A. I. Nahid, M. Oogane, H. Naganuma, Y. Ando

    IEEE TRANSACTIONS ON MAGNETICS 46 (6) 1637-1640 2010年6月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2010.2043223  

    ISSN:0018-9464

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    In this work, we have presented the electrical characteristic of Co2MnSi/MgO/n-Si junctions as a function of the doping concentration of Si. Films were fabricated by dc sputtering and post annealed at 400 degrees C for 1 h without breaking the vacuum. The Co2MnSi/MgO/n-Si junctions exhibited diode like characteristics at low doping concentration 10(16)/cc. This can be attributed due to oxide charges or interface traps close to the silicon interface, which causes the bend bending and forms the large extended depletion region. The junction characteristic was found to change with the increase of doping concentration and became symmetric at doping concentration of 10(19)/cc. Therefore, with the same thickness of MgO barrier, the junction characteristic was changed from Schottky to symmetric tunneling with the doping density of Si. The origin of the change of junction characteristic might be due to the change of the depletion width with the doping density.

  181. Fabrication of perpendicularly magnetized magnetic tunnel junctions with [formula omitted] hybrid electrode 査読有り

    T. Hiratsuka, G. Kim, Y. Sakuraba, T. Kubota, K. Kodama, N. Inami, H. Naganuma, M. Oogane, T. Nakamura, K. Takanashi, Y. Ando

    Journal of Applied Physics 107 (9) 2010年5月1日

    DOI: 10.1063/1.3358239  

    ISSN:1089-7550 0021-8979

    eISSN:1089-7550

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    Magnetic tunnel junctions (MTJs) of perpendicularly magnetized [formula omitted] structure were fabricated. In-plane x-ray diffraction measurements and element specific evaluation of magnetic properties using soft x-ray magnetic circular dichroism were carried out to examine quite thin [formula omitted] (CMS) inserted layer between CoPt and MgO interface. Ordered [formula omitted] was successfully fabricated onto [formula omitted] as thin as 1 nm thick, and CMS layer shows perpendicular magnetic anisotropy below 3 nm thick via exchange coupling with CoPt layer. In the MTJ-stacking, epitaxial growth was confirmed except for partial misalignment in the upper FePt layer, and coercive field difference clearly appeared between the bottom and the top ferromagnetic electrodes. © 2010, American Institute of Physics. All rights reserved.

  182. Fabrication of perpendicularly magnetized magnetic tunnel junctions with L1(0)-CoPt/Co2MnSi hybrid electrode 査読有り

    T. Hiratsuka, G. Kim, Y. Sakuraba, T. Kubota, K. Kodama, N. Inami, H. Naganuma, M. Oogane, T. Nakamura, K. Takanashi, Y. Ando

    JOURNAL OF APPLIED PHYSICS 107 (9) 2010年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3358239  

    ISSN:0021-8979

    eISSN:1089-7550

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    Magnetic tunnel junctions (MTJs) of perpendicularly magnetized L1(0)-CoPt/Co2MnSi/MgO/FePt structure were fabricated. In-plane x-ray diffraction measurements and element specific evaluation of magnetic properties using soft x-ray magnetic circular dichroism were carried out to examine quite thin Co2MnSi (CMS) inserted layer between CoPt and MgO interface. Ordered B2-CMS was successfully fabricated onto L1(0)-CoPt as thin as 1 nm thick, and CMS layer shows perpendicular magnetic anisotropy below 3 nm thick via exchange coupling with CoPt layer. In the MTJ-stacking, epitaxial growth was confirmed except for partial misalignment in the upper FePt layer, and coercive field difference clearly appeared between the bottom and the top ferromagnetic electrodes. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3358239]

  183. High efficient spin transfer torque writing on perpendicular magnetic tunnel junctions for high density MRAMs 査読有り

    Tatsuya Kishi, Toshihiko Nagase, Masatoshi Yoshikawa, Katsuya Nishiyama, Eiji Kitagawa, Tadaomi Daibou, Minoru Amano, Naoharu Shimomura, Shigeki Takahashi, Tadashi Kai, Masahiko Nakayama, Hisanori Aikawa, Sumio Ikegawa, Makoto Nagamine, Junichi Ozeki, Shigemi Mizukami, Mikihiko Oogane, Yasuo Ando, Shinji Yuasa, Kei Yakushiji, Hitoshi Kubota, Yoshishige Suzuki, Yoshinobu Nakatani, Terunobu Miyazaki, Koji Ando

    Curr. Appl. Phys. 10 (1) e87-89 2010年4月

    出版者・発行元:None

    DOI: 10.1016/j.cap.2009.12.021  

    ISSN:1567-1739

    eISSN:1878-1675

  184. Gilbert damping in perpendicularly magnetized Pt/Co/Pt films investigated by all-optical pump-probe technique 査読有り

    S. Mizukami, E. P. Sajitha, D. Watanabe, F. Wu, T. Miyazaki, H. Naganuma, M. Oogane, Y. Ando

    APPLIED PHYSICS LETTERS 96 (15) 2010年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3396983  

    ISSN:0003-6951

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    To investigate the correlation between perpendicular magnetic anisotropy and intrinsic Gilbert damping, time-resolved magneto-optical Kerr effect was measured in Pt/Co(d(Co))/Pt films. These films showed perpendicular magnetization at d(Co)=1.0 nm and a perpendicular magnetic anisotropy energy K(u)(eff) that was inversely proportional to d(Co). With an analysis based on the Landau-Lifshitz-Gilbert equation, the intrinsic Gilbert damping constant alpha was evaluated by parameter-fitting of frequency and lifetime expressions to experimental data of angular variations in spin precession frequency and life-times. The alpha values increased significantly with decreasing d(Co) but not inversely proportional to d(Co).

  185. Reproducible trajectory on subnanosecond spin-torque magnetization switching under a zero-bias field for MgO-based ferromagnetic tunnel junctions 査読有り

    Tatsuya Aoki, Yasuo Ando, Mikihiko Oogane, Hiroshi Naganuma

    APPLIED PHYSICS LETTERS 96 (14) 2010年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3380595  

    ISSN:0003-6951

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    One of the features of spin-transfer torque (STT)-based magnetic random access memories (spin-RAMs) is a fast write cycle; however, switching properties in the subnanosecond regime for MgO-based magnetic tunnel junctions (MTJs) are still unclear. In this work, we demonstrated subnanosecond magnetization switching by STT for MgO-based MTJs. We also discuss the thermal effect on subnanosecond STT switching, as well as the subnanosecond pulse width that is dependent on the remarkable plateau that switching probability has under a zero-bias field.

  186. Epitaxial growth of Co2MnSi thin films at the vicinal surface of n-Ge(111) substrate 査読有り

    M. A. I. Nahid, M. Oogane, H. Naganuma, Y. Ando

    APPLIED PHYSICS LETTERS 96 (14) 2010年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3378986  

    ISSN:0003-6951

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    The structure and magnetic properties of Co2MnSi films on n-Ge(111) substrate were investigated for the motivation of spin injection. The 50-nm-thick Co2MnSi films were fabricated on n-Ge(111) substrates by dc sputtering and postannealed about 1 h at the various temperatures ranging from 200-500 degrees C. In the annealing temperature range of 300-400 degrees C, the Co2MnSi were grown epitaxially at the vicinal surface of n-Ge(111) substrates. The epitaxial layer of Co2MnSi films was about 18 nm thick at 350 degrees C and exhibited ferromagnetic behavior. Interestingly, there was no diffusion of Ge inside the epitaxial layer and atomically flat interface was obtained.

  187. Evidence of Fermi level control in a half-metallic Heusler compound Co2MnSi by Al-doping: Comparison of measurements with first-principles calculations 査読有り

    Y. Sakuraba, K. Takanashi, Y. Kota, T. Kubota, M. Oogane, A. Sakuma, Y. Ando

    PHYSICAL REVIEW B 81 (14) 2010年4月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.81.144422  

    ISSN:2469-9950

    eISSN:2469-9969

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    The Fermi level (E-F) control of half-metallic Heusler alloy Co2MnSi by Al-doping was challenged in magnetic tunnel junctions with a Co2MnAlxSi1-x (CMAS) electrode. The observed bias voltage dependence on tunneling conductance (G-V curves) clearly shows a shift in E-F toward the center of the half-metallic gap with x, which showed excellent agreement with our first-principles calculations. However, the ratio of tunnel magnetoresistance (TMR) at 10 K to that at room temperature does not exhibit a remarkable change with x. The weak exchange energy at the CMAS interface may be the origin for the large temperature dependence of the TMR ratio.

  188. Element-Specific Evaluation of Magnetic Moments in Ferrimagnetic Mn2Val Heusler Epitaxial Thin Films 査読有り

    T.Kubota, K. Kodama, T. Nakamura, Y. Sakuraba, M. Oogane, H. Naganuma, K. Takanashi, Y. Ando

    J. Magn. Soc. Jpn. 34 (2) 100-106 2010年3月

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.1002R0004  

    ISSN:1882-2924

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    We successfully fabricated <i>L</i>2<sub>1</sub>-ordered Mn<sub>2</sub>VAl Heusler thin films and evaluated their ferrimagnetic properties by soft x-ray magnetic circular dichroism (XMCD). The buffer layers and annealing temperatures were varied to prepare the Mn<sub>2</sub>VAl films. We discovered that Mn<sub>2</sub>VAl could be ordered in an <i>L</i>2<sub>1</sub> phase well when it was deposited directly onto an MgO (001) single crystalline substrate. The maximum values of <i>L</i>2<sub>1</sub> and <i>B</i>2 long-range order parameters we obtained were about 0.5 for both phases for samples without a buffer layer, when substrates were heated at 500°C or 600°C. The saturation magnetization (<i>M</i><sub>s</sub>) for these samples was roughly 150 emu/cc. This is rather small compared to that expected from the ideal Slater-Pauling behavior, which might be due to the suppressed degree of <i>L</i>2<sub>1</sub> or <i>B</i>2 ordering. Ferrimagnetism in the Mn<sub>2</sub>VAl, ferrimagnetic coupling between Mn and V moments was clearly observed by using the XMCD technique in well-ordered <i>L</i>2<sub>1</sub>-Mn<sub>2</sub>VAl film as has been predicted in theoretical investigations.

  189. Co-concentration dependence of half-metallic properties in Co–Mn–Si epitaxial films 査読有り

    Y. Sakuraba, N. Hirose, M. Oogane, T. Nakamura, Y. Ando, K. Takanashi

    Appl. Phys. Lett. 96 (9) 2010年3月

    出版者・発行元:None

    DOI: 10.1063/1.3330942  

    ISSN:0003-6951

    eISSN:1077-3118

  190. Optically induced magnetization dynamics and variation of damping parameter in epitaxial Co2MnSi Heusler alloy films 査読有り

    Y. Liu, L. R. Shelford, V. V. Kruglyak, R. J. Hicken, Y. Sakuraba, M. Oogane, Y. Ando

    PHYSICAL REVIEW B 81 (9) 2010年3月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.81.094402  

    ISSN:2469-9950

    eISSN:2469-9969

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    All-optical pump-probe measurements of magnetization dynamics have been performed upon epitaxial Co2MnSi(001) Heusler alloy thin films annealed at temperatures of 300, 400, and 450 degrees C. An ultrafast laser-induced modification of the magnetocrystalline anisotropy triggers precession which is detected by time-resolved magneto-optical Kerr effect measurements. From the damped oscillatory Kerr rotation, the frequency and relaxation rate of the precession is determined. Using a macrospin solution of the Landau-Lifshitz-Gilbert equation the effective fields acting upon the sample magnetization are deduced. This reveals that the magnetization is virtually independent of the annealing temperature while the fourfold magnetocrystalline anisotropy decreases dramatically with increasing annealing temperature as the film structure changes between the B2 and L2(1) phases. From the measured relaxation rates, the value of the apparent Gilbert damping parameter is found to depend strongly upon the static field strength and in-plane static field orientation. The variation of the apparent damping parameter is generally well reproduced by an inhomogeneous broadening model in which the presence of B2 and L2(1) phases leads to a large dispersion of the magnetocrystalline anisotropy. However, for the sample annealed at a temperature of 300 degrees C, the lack of a detailed fit to the data suggests that the apparent anisotropy of the apparent damping parameter might alternatively arise due to a network of dislocations with fourfold symmetry.

  191. Structural and magnetic properties of Mn(2.5)Ga films 査読有り

    F. Wu, S. Mizukami, D. Watanabe, H. Naganuma, M. Oogane, Y. Ando, T. Miyazaki

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 062037-1-062037-5 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/6/062037  

    ISSN:1742-6588

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    In this work polycrystalline and epitaxial Mn(2.5)Ga films were prepared by dc magnetron sputtering technique. The lower sputtering power and higher annealing temperature are found to be beneficial for increasing ratio of DO(22) phase in the polycrystalline Mn2.5Ga films, leading to the improved magnetic properties although perpendicular magnetic anisotropy (PMA) properties cannot be observed. On the contrary, (001)-oriented epitaxial Mn(2.5)Ga films grown on Cr buffered MgO substrates possess low saturation magnetization and giant PMA properties simultaneously.

  192. Structural characterization of epitaxial multiferroic BiFeO<SUB>3</SUB> films grown on SrTiO<SUB>3</SUB> (100) substrates by crystallizing amorphous Bi-Fe-O<SUB>x</SUB> 査読有り

    H. Naganuma, T. Miyazaki, A. Ukachi, M. Oogane, S. Miukami, Y. Ando

    J. Ceramic Soc. Jpn. 118 (1380) 648-651 2010年

    出版者・発行元:公益社団法人 日本セラミックス協会

    DOI: 10.2109/jcersj2.118.648  

    ISSN:1882-0743

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    Amorphous Bi–Fe–O<i><sub>x</sub></i> films prepared on SrTiO<sub>3</sub> (100) substrates using a conventional r.f. magnetron sputtering system were crystallized by post-annealing at 873 K in an atmosphere. Microstructural observations by X-ray diffraction and cross-sectional transmission electron microscopy revealed that the crystallized Bi–Fe–O<i><sub>x</sub></i> films were well-epitaxially BiFeO<sub>3</sub> fabricated without interfacial layer although as-prepared film was amorphous structure with excess Bi. The crystallized BiFeO<sub>3</sub> films have fairly epitaxial compatibly ([001](001)BiFeO<sub>3</sub> // [001](001)SrTiO<sub>3</sub>). These results indicate that (1) BiFeO<sub>3</sub> has good epitaxial compatibility with SrTiO<sub>3</sub> and (2) crystallizing amorphous Bi–Fe–O<i><sub>x</sub></i> is one possible method that can be used to fabricate high-quality multiferroic barriers for tunnel junctions.

  193. Electrical transport properties of perpendicular magnetized Mn-Ga epitaxial films 査読有り

    Feng Wu, E. P. Sajitha, Shigemi Mizukami, Daisuke Watanabe, Terunobu Miyazaki, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    APPLIED PHYSICS LETTERS 96 (4) 2010年1月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3298363  

    ISSN:0003-6951

    eISSN:1077-3118

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    We report electrical transport properties of perpendicular magnetized Mn-Ga epitaxial films with various thicknesses. The maximum extraordinary Hall resistivity and Hall angle is 11.5 mu cm and 5.7%, respectively, which is comparable to the highest value reported in amorphous Fe0.79Gd0.21 alloy. In the low temperature region, resistivity was proportional to T-2.9 owing to the unconventional one-magnon scattering processes, indicating high spin polarization of this material.

  194. Magnetoresistance of Perpendicularly Magnetized Tunnel Junction Using L1(0)-CoNiPt with Low Saturation Magnetization 査読有り

    G. Kim, T. Hiratsuka, H. Naganuma, M. Oogane, Y. Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/5/052011  

    ISSN:1742-6588

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    Investigations of the structural and magnetic properties of thin Co(50-x)Ni(x)Pt(50) (x = 0, 10, 15, 37.5) films and fabrication of magnetic tunnel junctions (MTJs) using Co(50)Pt(50) and Co(35)Ni(15)Pt(50) electrodes were performed. X-ray diffraction analyses revealed that 20-nm-thick CoPt and CoNiPt films were epitaxially grown with (001)-orientation with an L1(0)-chemical order parameter of 0.66-0.82. CoNiPt with various Ni contents magnetized perpendicularly; the saturation magnetization reduced to 157 emu/cm(3) when the Ni content was increased to 37.5%. Magnetotransport measurements under a magnetic field applied perpendicular to the film plane revealed a tunnel magnetoresistance ratio of 10% and 1% at 10 K and 300 K, respectively, for MTJ using Co(35)Ni(15)Pt(50) electrodes.

  195. Structural, Magnetic, and Magnetotransport Properties of FePt/MgO/CoPt Perpendicularly Magnetized Tunnel Junctions 査読有り

    N. Inami, G. Kim, T. Hiratsuka, H. Naganuma, M. Oogane, Y. Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/5/052008  

    ISSN:1742-6588

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    Perpendicularly magnetized magnetic tunnel junctions (MTJs) were fabricated by depositing thin L1(0)-ordered FePt films on MgO(001) substrates using a UHV sputtering system, and the dependence of structural, magnetic, magnetotransport properties of the junctions on the thickness of the FePt layers was investigated. A full epitaxial structure was observed when the thickness of the L1(0)-ordered FePt film was 4 nm. The tunnel magnetoresistance (TMR) ratio was measured to be 6% at room temperature, and magnetization switching was clearly observed in the thin FePt layer.

  196. Magnetotransport properties of CoFeB/MgO/CoFe/MgO/CoFeB double barrier magnetic tunnel junctions with large negative magnetoresistance at room temperature 査読有り

    L. X. Jiang, H. Naganuma, M. Oogane, K. Fujiwara, T. Miyazaki, K. Sato, T. J. Konno, S. Mizukami, Y. Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/5/052009  

    ISSN:1742-6588

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    CoFeB/MgO/CoFe/MgO/CoFeB double-barrier magnetic-tunnel junctions were fabricated using an ultrahigh vacuum magnetron sputtering system, and their magnetotransport properties were characterized at room temperature. After post-deposition annealing, the polarity of TMR changed from negative to positive with increasing bias voltage. A relatively high negative TMR ratio of 30% was obtained at a negative bias voltage. Furthermore, a unique bias voltage dependence of conductance was observed at room temperature. This behavior may be attributable to the large minority density of states caused by the interfacial oxidation of the middle CoFe layer.

  197. Ultrafast Demagnetization for Ni80Fe20 and Half-metallic Co2MnSi Heusler Alloy Films 査読有り

    S. Mizukami, S. Tunegi, T. Kubota, M. Oogane, D. Watanabe, H. Naganuma, Y. Ando, T. Miyazaki

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/4/042017  

    ISSN:1742-6588

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    We investigated ultrafast demagnetization for NM/Ni80Fe20 (Py)/NM (NM=Ta,Pt) and epitaxial half-metallic Co2MnSi (CMS) films using an all-optical pump-probe technique to clarify the correlation between demagnetization time tau(M) and magnetic damping constant alpha or spin polarization. The signal from the all-optical time-resolved magneto-optical Kerr effect exhibited rapid decrease in the sub-ps time regime and damped oscillations for these films. Values of tau(M) and alpha were evaluated using the three-temperature model and the Landau-Lifshitz-Gilbert equation. The alpha values for the NM/Py/NM films depended on both the Py thickness and NM materials while tau M was almost constant. The tau(M) values for the epitaxial CMS films were almost independent of L2(1)-ordering and a little shorter than those for NM/Py/NM films.

  198. Interlayer exchange coupling in perpendicularly magnetized synthetic ferrimagnet structure using CoCrPt and CoFeB 査読有り

    D. Watanabe, S. Mizukami, F. Wu, M. Oogane, H. Naganuma, Y. Ando, T. Miyazaki

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/7/072104  

    ISSN:1742-6588

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    Interlayer exchange coupling in synthetic ferrimagnet structures consisting of perpendicularly magnetized CoCrPt and in-plane magnetized CoFeB layers, which are coupled by a Ru thin spacer, were investigated. The magnetization of the CoFeB layer turned perpendicular to the film plane after annealing at 300 degrees C because of the appearance of interlayer coupling from the CoCrPt layer. The coupling varied between antiferromagnetic and ferromagnetic depending on the Ru spacer thickness. The sign and strength of the coupling were also observed through analyses of magnetization curves and ferromagnetic resonance spectra.

  199. Spin-transfer Switching in Magnetic Tunnel Junctions with Synthetic Ferri-magnetic Free Layer 査読有り

    M. Nishimura, M. Oogane, H. Naganuma, N. Inami, S. Ikeda, H. Ohno, Y. Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/5/052018  

    ISSN:1742-6588

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    We have fabricated the SyF structure with both high annealing stability and strong interlayer exchange coupling and investigated tunnelling magnetoresistance (TMR) and spin-transfer switching properties of magnetic tunnel junctions (MTJs) with developed SyF free layer. The fabricated SyF with structure of Ta/Ru/CoFe/Ru/CoFeB possessed high annealing stability of 400 degrees C and strong interlayer exchange coupling. Consequently, a large TMR ratio of 122% has been observed after annealing at high temperature of 350 degrees C. In addition, we have successfully observed spin-transfer switching by the net current density of 14 MA/cm(2) and the large thermal stability factor of 62.

  200. Synthetic CoFeB/Ru/NiFe Free Layer on MgO Barrier Layer for Spin Transfer Switching 査読有り

    Takuya Ono, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/6/062019  

    ISSN:1742-6588

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    In order to study the application potential of spin transfer switching in magnetic tunnel junctions (MTJs), a synthetic parallelly coupled layered structure such as a hard CoFeB/Ru/soft NiFe layers deposited on a MgO layer is investigated. The magnetic coupling between the layers is maintained after post-annealing at 300 degrees C, while annealing at 350 degrees C reduces the coupling strength. The observation of spin transfer switching in the junction indicates that parallel-to-antiparallel transition does not occur when the applied current pulse width is in the sub-millisecond range, which is far from the precessional range. This result indicates that spin transfer from NiFe to CoFeB might affect the dynamics of CoFeB magnetization.

  201. Spin transistor based on double tunnel junctions using half-metallic Co2MnSi electrodes 査読有り

    Yusuke Ohdaira, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/200/5/052019  

    ISSN:1742-6588

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    Magnetic tunnel junctions (MTJs) using half-metallic Heusler alloy Co2MnSi electrodes show large tunnel magnetoresistance (TMR) ratio and large bias voltage dependence of tunnel conductance. We propose a spin transistor utilizing half-metallic characteristics of Co2MnSi. Fundamental structure is double tunnel junctions using Co2MnSi electrodes with gate electrode. The bias voltage dependence of tunnel conductance for the fabricated device has shown half-metallic characteristic of Co2MnSi electrodes. The TMR ratio has decreased with increasing gate voltage. This is the first observation of modulating the tunnel conductance by applying an external voltage in spin transistor using Co2MnSi.

  202. Dynamic Magnetic Intermediate State during Nanosecond Spin Transfer Switching for MgO-Based Magnetic Tunnel Junctions 査読有り

    Tatsuya Aoki, Yasuo Ando, Mikihiko Oogane, Hiroshi Naganuma

    APPLIED PHYSICS EXPRESS 3 (5) 2010年

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.3.053002  

    ISSN:1882-0778

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    We report for the first time that the dynamic magnetic intermediate state (DMI) was observed at a speed of several ns during spin transfer switching for MgO-based magnetic tunnel junctions (MTJs). The DMI was observed as slow resistance oscillation at the center of the parallel to anti-parallel state by single shot time domain measurements. The DMI is observable at certain current amplitudes. The outbreak probability decreases with further current increase. We concluded that the DMI originates from inhomogeneous magnetization behavior. On the other hand, previous single shot time domain measurements have shown only for single-domain-like magnetization behavior. (C) 2010 The Japan Society of Applied Physics

  203. Structure, exchange stiffness, and magnetic anisotropy of Co2MnAlxSi1-x Heusler compounds 査読有り

    Takahide Kubota, Jaroslav Hamrle, Yuya Sakuraba, Oksana Gaier, Mikihiko Oogane, Akimasa Sakuma, Burkard Hillebrands, Koki Takanashi, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 106 (11) 2009年12月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3265428  

    ISSN:0021-8979

    eISSN:1089-7550

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    We have investigated the exchange constant A (exchange stiffness D) and the magnetic anisotropy of Co2MnAlxSi1-x (CMAS) Heusler compounds as a function of the film composition. In case of Co2MnSi, A was found to be 23.5 pJ/m (D=5.86 meV nm(2)). Furthermore, A decreased with an increase in the Al content x. In the case of Co2MnAl, it was found to be 4.8 pJ/m (D=1.90 meV nm(2)). Finally, the cubic anisotropy constant K-1 of CMAS films was found to be small (below 10 kJ/m(3)) and did not exhibit simple dependence on x.

  204. Ferrimagnetism in epitaxially grown Mn2VAl Heusler alloy investigated by means of soft x-ray magnetic circular dichroism 査読有り

    Takahide Kubota, Kenji Kodama, Tetsuya Nakamura, Yuya Sakuraba, Mikihiko Oogane, Koki Takanashi, Yasuo Ando

    APPLIED PHYSICS LETTERS 95 (22) 2009年11月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3269609  

    ISSN:0003-6951

    eISSN:1077-3118

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    Epitaxially grown Mn2VAl films were fabricated on MgO (001) single crystalline substrates by using a sputtering technique. The resulting Mn2VAl films with substrate temperatures of T-s=500 and 600 degrees C showed an L2(1)-ordered structure. The saturation magnetization was 150 emu/cm(3) at 300 K for a sample with T-s=600 degrees C. Ferrimagnetic coupling between the Mn and V magnetic moments in the L2(1)-Mn2VAl film was clearly demonstrated by soft x-ray magnetic circular dichroism. In previous studies, this coupling was found only in polycrystalline bulk samples examined by nuclear magnetic resonance.

  205. The effect of MgO barrier on the structure and magnetic properties of Co2MnSi films on n-Si(100) substrates 査読有り

    M. A. I. Nahid, M. Oogane, H. Naganuma, Y. Ando

    JOURNAL OF APPLIED PHYSICS 106 (10) 2009年11月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3260253  

    ISSN:0021-8979

    eISSN:1089-7550

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    We investigated the structure and magnetic properties of Co2MnSi/MgO/n-Si(100) films with the goal of achieving efficient spin injection. The Co2MnSi films were fabricated by dc sputtering and post annealed at 400 degrees C for 1 h. They were oriented along the &lt; 100 &gt; direction with a MgO barrier layer. A strong chemical reaction was observed between the Co2MnSi thin films and n-Si substrates in the absence of the MgO barrier. The diffusion or chemical reaction may occur up to a MgO layer thickness of 2 nm. With a MgO layer that is 2 nm thick, Co2MnSi possessed large saturation magnetization and low surface roughness at room temperature. The electrical (I-V) characteristics of Co2MnSi/MgO(2 nm)/n-Si(100) obtained at various junction sizes were symmetric, suggesting that MgO was an effective tunnel barrier. (C) 2009 American Institute of Physics. [doi:10.1063/1.3260253]

  206. Tunnel magnetoresistance in epitaxially grown magnetic tunnel junctions using Heusler alloy electrode and MgO barrier 査読有り

    S. Tsunegi, Y. Sakuraba, M. Oogane, N. D. Telling, L. R. Shelford, E. Arenholz, G. van der Laan, R. J. Hicken, K. Takanashi, Y. Ando

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 (19) 2009年10月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/42/19/195004  

    ISSN:0022-3727

    eISSN:1361-6463

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    Epitaxially grown magnetic tunnel junctions (MTJs) with a stacking structure of Co2MnSi/MgO/CoFe were fabricated. Their tunnel magnetoresistance (TMR) effects were investigated. The TMR ratio and tunnelling conductance characteristics of MTJs were considerably different between those with an MgO barrier prepared using sputtering (SP-MTJ) and those prepared using EB evaporation (EB-MTJ). The EB-MTJ exhibited a very large TMR ratio of 217% at room temperature and 753% at 2K. The bias voltage dependence of the tunnelling conductance in the parallel magnetic configuration for the EB-MTJ suggests that the observed large TMR ratio at RT results from the coherent tunnelling process through the crystalline MgO barrier. The tunnelling conductance in the anti-parallel magnetic configuration suggests that the large temperature dependence of the TMR ratio results from the inelastic spin-flip tunnelling process.

  207. Study of Structure, Magnetic and Electrical Properties of Co2MnSi Heusler Alloy Thin Films Onto n-Si Substrates 査読有り

    M. A. I. Nahid, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    IEEE TRANSACTIONS ON MAGNETICS 45 (10) 4030-4032 2009年10月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2009.2024320  

    ISSN:0018-9464

    eISSN:1941-0069

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    The structural, magnetic and electrical properties of Co2MnSi thin films grown onto n-doped Si(110) and n-Si(100) substrates were studied. The structure and magnetic properties of Co2MnSi thin films were found to depend strongly on the annealing temperature (T-A). At T-A = 275-350 degrees C, the Co2MnSi films were of B2 phase with &lt; 100 &gt; texture and possessed magnetic moment on both substrates. The saturation magnetization (M-S) of Co2MnSi thin films was found maximum at T-A = 300 degrees C. Chemical reaction might occur between Co2MnSi and Si above T-A = 350 degrees C which caused nearly zero M-S value. The current-voltage (I-V) characteristic of the Co2MnSi thin films onto n-Si substrates was obtained linear suggesting the contacts were ohmic nature.

  208. Direct Observation of Atomic Ordering and Interface Structure in Co2MnSi/MgO/Co2MnSi Magnetic Tunnel Junctions by High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy 査読有り

    Toyoo Miyajima, Mikihiko Oogane, Yasutoshi Kotaka, Takashi Yamazaki, Mineharu Tsukada, Yuji Kataoka, Hiroshi Naganuma, Yasuo Ando

    APPLIED PHYSICS EXPRESS 2 (9) 2009年9月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.2.093001  

    ISSN:1882-0778

    eISSN:1882-0786

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    The atomic ordering of Co2MnSi (CMS) full-Heusler film and the interface structure of CMS/MgO/CMS magnetic tunnel junctions (MTJs) were investigated by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). We observed the atomic ordering of L2(1) and B2 structures of CMS from the atomic number (Z) contrast STEM images. We also confirmed that the interface structure consists of the layer next to the Co layer terminating in the CMS to MgO layer from the layer periodicity along the [001] direction, however, site-disorder exists between two atomic layers at the termination of CMS, including locally L2(1)-ordered MnSi terminated structure. (C) 2009 The Japan Society of Applied Physics

  209. Structural and Magnetic Properties of CO2MnSi Heusler Alloy Thin Films on Si 査読有り

    Muhammad Ariful Islam Nahid, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando

    JAPANESE JOURNAL OF APPLIED PHYSICS 48 (8) 2009年8月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.48.083002  

    ISSN:0021-4922

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    The structural and magnetic properties of CO2MnSi thin films grown on n-doped Si(110) and Si(100) substrates were studied and observed to have a strong dependence on annealing temperature (T-A). At T-A = 275-350 degrees C, the CO2MnSi films exhibited the B2 phase with a &lt; 100 &gt; orientation and a magnetic moment on both substrates. The saturation magnetization (M-S) of CO2MnSi thin films was observed to reach a maximum at T-A = 300 degrees C, above which it was found to decrease. We consider that at T-A similar or equal to 300 degrees C, the CO2MnSi thin films on Si substrates exhibited the (100) orientation, a high M-S and a low roughness which might promote spin injection. (C) 2009 The Japan Society of Applied Physics

  210. Large Tunnel Magnetoresistance of 1056% at Room Temperature in MgO Based Double Barrier Magnetic Tunnel Junction (Retracted article. See vol. 4, artn no. 019201, 2011) 査読有り

    Lixian Jiang, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando

    APPLIED PHYSICS EXPRESS 2 (8) 2009年8月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.2.083002  

    ISSN:1882-0778

    eISSN:1882-0786

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    CoFeB/MgO/CoFeB/MgO/CoFeB double barrier magnetic tunnel junctions (DBMTJs) with thin middle layers were fabricated on SiO2/Si(001) substrates by r.f. magnetron sputtering. We successfully obtained a large tunnel magnetoresistance of 1056% at room temperature in a DBMTJ with a middle CoFeB layer thickness of 1.2 nm that was fabricated at a relatively low post-deposition annealing temperature of 350 degrees C. This DBMTJ also realized sharp magnetization switching in the free middle CoFeB layer, which is attributed to strong antiferromagnetic coupling between the exterior CoFeB and PtMn layers. These favorable magnetoresistive properties offer interesting possibilities for developing practical spintronics applications and noble magnetotransport physics. (C) 2009 The Japan Society of Applied Physics

  211. Enhancement in tunnel magnetoresistance effect by inserting CoFeB to the tunneling barrier interface in Co2MnSi/MgO/CoFe magnetic tunnel junctions 査読有り

    S. Tsunegi, Y. Sakuraba, M. Oogane, Hiroshi Naganuma, K. Takanashi, Y. Ando

    APPLIED PHYSICS LETTERS 94 (25) 2009年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3156858  

    ISSN:0003-6951

    eISSN:1077-3118

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    Tunnel magnetoresistance (TMR) effect was investigated in Co2MnSi/CoFeB(0-2 nm)/MgO/CoFe magnetic tunnel junctions (MTJs). TMR ratio was enhanced by inserting a thin CoFeB layer at the Co2MnSi/MgO interface. The MTJ with CoFeB thickness of 0.5 nm exhibited the highest TMR ratio. From the conductance-voltage measurements for the fabricated MTJs, we infer that the highly spin polarized electron created in Co2MnSi can conserve the polarization through the 0.5-nm-thick CoFeB layer. Furthermore, by insertion of the thin CoFeB layer, the temperature dependence of the TMR ratio was improved because of the suppression of the fluctuation of the magnetic moment at the Co2MnSi/MgO interface.

  212. Fabrication of MgO-based magnetic tunnel junctions with CoCrPt perpendicularly magnetized electrodes 招待有り 査読有り

    Daisuke Watanabe, Shigemi Mizukami, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 105 (7) 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3062816  

    ISSN:0021-8979

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    The applicability of perpendicularly magnetized CoCrPt films to the MgO-based magnetic tunnel junctions (MTJs) was investigated. For this study, CoCrPt films deposited on the Ru buffer exhibited hcp(0002)-oriented growth by sputtering method using the low substrate temperature of 250 degrees C, low saturation magnetization of around 360 emu/cm(3), and high magnetic anisotropy field of 6 kOe, which is sufficient to retain the thermal stability of the magnetization direction. The MgO-based MTJs with a synthetic ferrimagnetlike structure were fabricated: CoFe was coupled magnetically with CoCrPt through the thin Ru layer. Transport properties with a magnetic field applied perpendicular to the film plane revealed a tunnel magnetoresistance ratio of about 6% at room temperature. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062816]

  213. Low damping constant for Co2FeAl Heusler alloy films and its correlation with density of states 査読有り

    S. Mizukami, D. Watanabe, M. Oogane, Y. Ando, Y. Miura, M. Shirai, T. Miyazaki

    JOURNAL OF APPLIED PHYSICS 105 (7) 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3067607  

    ISSN:0021-8979

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    Gilbert damping for the epitaxial Co2FeAl Heusler alloy films was investigated. Gilbert damping constant for the films was evaluated by analyzing the data of ferromagnetic resonance measured at the frequency of 2-20 GHz. Gilbert damping constant for the film without annealing was rather large, while it decreased remarkably with postannealing. Gilbert damping constant for the film annealed at 600 degrees C was similar or equal to 0.001. These behavior of Gilbert damping constant can be well explained by the fact that the density of states calculated from first principles decreases with increasing the degree of B2 order. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3067607]

  214. Tunnel magnetoresistance effect in double magnetic tunnel junctions using half-metallic Heusler alloy electrodes 招待有り 査読有り

    Yusuke Ohdaira, Mikihiko Oogane, Yasuo Ando

    JOURNAL OF APPLIED PHYSICS 105 (7) 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3072023  

    ISSN:0021-8979

    eISSN:1089-7550

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    Double magnetic tunnel junctions (DMTJs) using half-metallic Co2MnSi Heusler alloy electrodes were fabricated. Their tunnel magnetoresistance (TMR) effects were then investigated. Large TMR ratios were observed as 25% at room temperature and as 320% at 6 K. The bias voltage dependence of tunnel conductance suggests a half-metallic nature of the Co2MnSi electrode. These results show that high-quality DMTJ with half-metallic Heusler alloy electrodes was fabricated and that the DMTJ exhibited the expected performance. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3072023]

  215. Reduction in switching current using a low-saturation magnetization Co-Fe-(Cr, V)-B free layer in MgO-based magnetic tunnel junctions 査読有り

    Hitoshi Kubota, Akio Fukushima, Kay Yakushiji, Satoshi Yakata, Shinji Yuasa, Koji Ando, Mikihiko Ogane, Yasuo Ando, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 105 (7) 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3068484  

    ISSN:0021-8979

    eISSN:1089-7550

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    Magnetic properties, magnetoresistance (MR), and spin-transfer switching of magnetic tunnel junctions having a structure of Co60Fe20B20 3 nm/MgO 1 nm/(Co75Fe25)(80-X)Cr(V)(X)B-20 2 nm (X=0-25) were investigated. Magnetization of the (Co-Fe)-(Cr, V)-B free layer decreased from 1.2 T before substitution to 0.6 T at Cr of 10% (0.8 T at V of 10%). The MR ratio and a resistance-area product (RA) before substitution were, respectively, about 130% and about 2 Omega mu m(2). The MR ratio decreased to 80% at Cr of 10% and 40% at V of 10%. The RA values were almost independent of the composition. The intrinsic switching current density (J(c0)) decreased from 15 to 8 MA/cm(2) at Cr of 10% and 12 MA/cm(2) for V of 10%. Upon the further increase in Cr and V, stable switching was difficult to observe. In summary, J(c0) decreased to half in the case of Cr, but the effect was small for V. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068484]

  216. Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+ irradiation 査読有り

    O. Gaier, J. Hamrle, B. Hillebrands, M. Kallmayer, P. Poersch, G. Schoenhense, H. J. Elmers, J. Fassbender, A. Gloskovskii, C. A. Jenkins, C. Felser, E. Ikenaga, Y. Sakuraba, S. Tsunegi, M. Oogane, Y. Ando

    APPLIED PHYSICS LETTERS 94 (15) 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3119188  

    ISSN:0003-6951

    eISSN:1077-3118

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    The influence of 30 keV He+ ion irradiation on structural, electronic, and magnetic properties of Co2MnSi thin films with a partial B2 order was investigated. It was found that room temperature irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and element-specific magnetization toward the bulk properties of a well-ordered Co2MnSi Heusler compound.

  217. Electronic properties of Co2MnSi thin films studied by hard x-ray photoelectron spectroscopy 査読有り

    Siham Ouardi, Andrei Gloskovskii, Benjamin Balke, Catherine A. Jenkins, Joachim Barth, Gerhard H. Fecher, Claudia Felser, Mihaela Gorgoi, Marcel Mertin, Franz Schaefers, Eiji Ikenaga, Ke Yang, Keisuke Kobayashi, Takahide Kubota, Mikihiko Oogane, Yasuo Ando

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 (8) 2009年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/42/8/084011  

    ISSN:0022-3727

    詳細を見る 詳細を閉じる

    This work reports on the electronic properties of thin films of the Heusler compound Co2MnSi studied by means of hard x-ray photoelectron spectroscopy (HAXPES). The results of photoelectron spectroscopy from multilayered thin films excited by photons of 2-8 keV are presented. The measurements were performed on (substrate/buffer layer/Co2MnSi(z)/capping layer) multilayers with a thickness z ranging from 0 to 50 nm. It is shown that high energy spectroscopy is a valuable tool for non-destructive depth profiling. The experimentally determined values of the inelastic electron mean free path in Co2MnSi increase from about 19.5 to 67 angstrom on increasing the kinetic energy from about 1.9 to 6.8 keV. The influence of the thermal treatment of Co2MnSi thin films on the electronic properties was also explored. The structure of the thin films is significantly improved by heat treatment as revealed by x-ray diffraction. It was found that the electronic structure of annealed samples as measured by photoelectron spectroscopy is similar to that of a well-ordered bulk reference sample. The samples without heat treatment show strong deviations from the electronic structure of bulk material. The differences between the disordered and the ordered films are also observed in core level spectra. Chemical shifts of about 100 meV are observed at the Mn 2p states. The stronger localization of the Mn d states in the ordered samples is obvious from the multiplet satellite of the Mn 2p(3/2) state.

  218. Epitaxial Mn2.5Ga thin films with giant perpendicular magnetic anisotropy for spintronic devices 査読有り

    Feng Wu, Shigemi Mizukami, Daisuke Watanabe, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS LETTERS 94 (12) 2009年3月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3108085  

    ISSN:0003-6951

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    We report on epitaxial growth and magnetic properties of Mn2.5Ga thin films, which were deposited on Cr/MgO single crystal substrates by magnetron sputtering. X-ray diffraction results revealed the epitaxial relationships as Mn2.5Ga(001)[100]parallel to Cr(001)[110]parallel to MgO(001)[100]. The presence of (002) and (011) superlattice peaks indicates that the films were crystallized into DO22 ordered structures. The perpendicular magnetic anisotropy (PMA) properties were found to be related to the extent of DO22 chemical ordering. A giant PMA (K-u(eff)=1.2x10(7) erg/cm(3)) and low saturation magnetization (M-s=250 emu/cm(3)) can be obtained for the film with highest chemical ordering parameter (S=0.8).

  219. Half-metallicity and Gilbert damping constant in Co2FexMn1−xSi Heusler alloys depending on the film composition 査読有り

    T. Kubota, S. Tsunegi, M. Oogane, S. Mizukami, T. Miyazaki, H. Naganuma, Y. Ando

    Appl. Phys. Lett. 94 (12) 2009年3月

    出版者・発行元:None

    DOI: 10.1063/1.3105982  

    ISSN:0003-6951

    eISSN:1077-3118

  220. 高反平行結合強度を有する積層フェリ構造の開発 査読有り

    西村 真之, 渡邉 大輔, 大兼 幹彦, 安藤 康夫

    Journal of the Magnetics Society of Japan 33 (3) 266-269 2009年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.0903RE8054  

    ISSN:1882-2924

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    We investigated the dependencies of the saturation field, <i>H</i><sub>s</sub>, for synthetic ferrimagnetic (SyF) structures with various stacking structures on annealing temperature and Ru middle layer thickness. The buffer layer was optimized using Co<sub>75</sub>Fe<sub>25</sub>/Ru/Co<sub>75</sub>Fe<sub>25</sub>-SyF. The SyF on the Ta/Ru buffer layer demonstrated high annealing stability and large <i>H</i><sub>s</sub>. Moreover, we investigated the dependence on annealing temperature of <i>H</i><sub>s</sub> for Ta(5 nm)/Ru(5 nm)/ ferromagnetic-layer/Ru(0.8 nm)/Co<sub>40</sub>Fe<sub>40</sub>B<sub>20</sub>(2 nm) SyFs with various ferromagnetic layers. The SyFs using Co<sub>75</sub> Fe<sub>25</sub> and Ni<sub>80</sub>Fe<sub>20</sub> ferromagnetic layers exhibited high annealing stability and large <i>H</i><sub>s</sub>. The dependence on Ru middle layer thickness of <i>H</i><sub>s</sub> for the SyFs consisting of Ta(5 nm)/Ru(5 nm)/Co<sub>75</sub> Fe<sub>25</sub>(2 nm)/Ru(0.2-1.2 nm)/Co<sub>40</sub>Fe<sub>40</sub>B<sub>20</sub>(2 nm)/ MgO(2.5 nm)/Ta(10 nm) was investigated. As a result, we demonstrated the possibility of fabricating CoFeB/MgO/ CoFeB MTJs with SyF having both high annealing stability and strong interlayer exchange coupling.

  221. Co2FeMnSiホイスラー合金の磁気緩和定数 査読有り

    大兼 幹彦, 窪田 崇秀, 廣瀬 直紀, 安藤 康夫

    Journal of the Magnetics Society of Japan 33 (3) 270-273 2009年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.0903RE8063  

    ISSN:1882-2924

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    Magnetic damping constants of Co<sub>2</sub>Fe<sub>x</sub>Mn<sub>1-x</sub>Si (x = 0.0 - 1.0) Heusler alloy thin films have been investigated. Co<sub>2</sub>Fe<sub>x</sub>Mn<sub>1-x</sub>Si thin films were epitaxitially grown on the single crystal MgO(100) substrate using magnetron sputtering technique. Damping constants were estimated by analyzing the line width of ferromagnetic resonance (FMR) spectra. Damping constant of Co<sub>2</sub>Fe<sub>x</sub>Mn<sub>1-x</sub>Si films showed a minimum value of 0.003 at x = 0.4. This damping constant is very small compared with other ferromagnetic metals. Additionally, damping constants significantly increased above x = 0.6. In this article, the relationship between the damping constant and the half-metallicity of Co<sub>2</sub>Fe<sub>x</sub>Mn<sub>1-x</sub>Si films is discussed.

  222. Co2MnSiを電極とする微小二重トンネル接合の作製と評価 査読有り

    大平 祐介, 大兼 幹彦, 安藤 康夫

    Journal of the Magnetics Society of Japan 33 (3) 262-265 2009年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.0903RE8052  

    ISSN:1882-2924

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    Double magnetic tunnel junctions (DMTJs) using half-metallic Heusler alloy Co<sub>2</sub>MnSi electrodes were fabricated. A tunnel magneto-resistance ratio as large as 25% (at RT) and 320% (at 6 K) was observed in the DMTJs with various junction areas. The dependence of the tunnel magneto-resistance on bias voltage was a typical characteristic of DMTJs. These results indicate that high-quality DMTJs were stably fabricated.

  223. Boron Composition Dependence of Spin-Transfer Switching in Magnetic Tunnel Junctions with CoFeB Free Layers 査読有り

    Daisuke Watanabe, Mikihiko Oogane, Shigemi Mizukami, Yasuo Ando, Terunobu Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS 48 (1) 2009年1月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/JJAP.48.013001  

    ISSN:0021-4922

    eISSN:1347-4065

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    We investigated tunnel magnetoresistance (TMR) and magnetization switching due to spin-transfer torque in CoFeB/MgO/CoFeB junctions having three different free layer compositions, (Co50Fe50)(100-x)B-x (x = 20, 25, 30), and measured their magnetic properties, including magnetization (M-s) and Gilbert damping constant (alpha), which are theoretically predicted to contribute to the critical current density (J(c0)) for spin-transfer switching. We found that the J(c0) in the magnetic tunnel junctions (MTJs) with x = 30 became smaller than that in the MTJs with x = 20 despite having a lower TMR ratio and a larger alpha. We showed that the J(c0) for each composition tends to follow the theoretical relationship for the magnetic factor of the tree layer. (c) 2009 The Japan Society of Applied Physics

  224. Tunnel magnetoresistance effect in magnetic tunnel junctions using epitaxial Co2FeSi Heusler alloy electrode 査読有り

    M. Oogane, M. Shinano, Y. Sakuraba, Y. Ando

    J. Appl. Phys. 105 (7) 07C903-1-07C903-3 2009年

    出版者・発行元:American Institute of Physics

    DOI: 10.1063/1.3062814  

    ISSN:0021-8979

  225. Direct Observation of Atomic Ordering and Interface Structure 査読有り

    T. Miyajima, M. Oogane, Y. Kotaka, T. Yamazaki, M. Tsukada, Y. Kataoka, H. Naganuma, Y. Ando

    Appl. Phys. Express 2009年

  226. Evidence of local moment formation in Co-based Heusler alloys 査読有り

    Telling, ND, Keatley, PS, van der Laan, G, Hicken, RJ, Arenholz, E, Sakuraba, Y, Oogane, M, Ando, Y, Takanashi, K, Sakuma, A, Miyazaki, T

    Phys. Rev. B 78 (18) 184438 2008年11月

    DOI: 10.1103/PhysRevB.78.184438  

  227. Electrical conductance properties for magnetic tunnel junctions with MgO barriers 招待有り 査読有り

    K. Tamanoi, M. Sato, M. Oogane, Y. Ando, T. Tanaka, Y. Uehara, T. Uzumaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320 (22) 2959-2962 2008年11月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2008.08.004  

    ISSN:0304-8853

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    We measured inelastic electron tunneling (IET) spectra and conductance for MgO tunneling magnetoresistance (TMR) films to obtain information on the ferromagnetic/barrier layer interface. The IET spectra showed the difference between amorphous and crystalline structures in the barrier. In the magnetic tunnel junction (MTJ) with a crystalline barrier the IET spectra indicated an Mg-O phonon peak at a low bias voltage by measurement with a parallel magnetization configuration. On the other hand, no peak was observed in the MTJ with an amorphous barrier. (C) 2008 Elsevier B. V. All rights reserved.

  228. Large tunnel magnetoresistance in magnetic tunnel junctions using a Co2MnSi Heusler alloy electrode and a MgO barrier 査読有り

    Sumito Tsunegi, Yuya Sakuraba, Mikihiko Oogane, Koki Takanashi, Yasuo Ando

    APPLIED PHYSICS LETTERS 93 (11) 2008年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2987516  

    ISSN:0003-6951

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    A large tunnel magnetoresistance (TMR) ratio of 753% has been observed at 2 K in a magnetic tunnel junction (MTJ) using a Co2MnSi Heusler alloy electrode and a crystalline MgO tunnel barrier. This TMR ratio is the largest reported to date in MTJs using a Heusler alloy electrode. Moreover, we have observed a large TMR ratio of 217% at room temperature (RT). This TMR at RT is much larger than that of MTJs using an amorphous Al-oxide tunnel barrier. However, the temperature dependence of the TMR ratio is still large because of inelastic tunneling in the antiparallel magnetic configuration. (C) 2008 American Institute of Physics.

  229. Temperature dependence of the interface moments in Co2MnSi thin films 査読有り

    N. D. Telling, P. S. Keatley, L. R. Shelford, E. Arenholz, G. van der Laan, R. J. Hicken, Y. Sakuraba, S. Tsunegi, M. Oogane, Y. Ando, K. Takanashi, T. Miyazaki

    APPLIED PHYSICS LETTERS 92 (19) 2008年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2927482  

    ISSN:0003-6951

    eISSN:1077-3118

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    X-ray magnetic circular dichroism (XMCD) is utilized to explore the temperature dependence of the interface moments in Co2MnSi (CMS) thin films capped with aluminum. By increasing the thickness of the capping layer, we demonstrate enhanced interface sensitivity of the measurements. L2(1)-ordered CMS films show no significant temperature dependence of either the Co or Mn interface moments. However, disordered CMS films show a decreased moment at low temperature possibly caused by increased Mn-Mn antiferromagnetic coupling. It is suggested that for ordered L2(1) CMS films the temperature dependence of the tunneling magnetoresistance is not related to changes in the interface moments. (c) 2008 American Institute of Physics.

  230. Spin transfer switching in the nanosecond regime for CoFeB/MgO/CoFeB ferromagnetic tunnel junctions 査読有り

    Tatsuya Aoki, Yasuo Ando, Daisuke Watanabe, Mikihiko Oogane, Terunobu Miyazaki

    JOURNAL OF APPLIED PHYSICS 103 (10) 2008年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2930873  

    ISSN:0021-8979

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    Detailed spin transfer switching properties in the nanosecond region for CoFeB/MgO(001)/CoFeB magnetic tunnel junctions are reported. The switching current (I(C)) was greatly increased in the &lt; 10 ns region. This characteristic resembles that of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR), although both the junction geometry and resistance differ from those of a CPP-GMR device. We discussed the switching properties considering the contribution of high frequency loss and the theoretical limitation of the analytical model. Furthermore, we observed real-time switching in the nanosecond region. Using these results, we discuss the spin transfer switching mechanism in the nanosecond region with both adiabatic and thermally activated models. (C) 2008 American Institute of Physics.

  231. Influence of the L2(1) ordering degree on the magnetic properties of Co2MnSi Heusler films 査読有り

    O. Gaier, J. Hamrle, S. J. Hermsdoerfer, H. Schultheiss, B. Hillebrands, Y. Sakuraba, M. Oogane, Y. Ando

    JOURNAL OF APPLIED PHYSICS 103 (10) 2008年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2931023  

    ISSN:0021-8979

    eISSN:1089-7550

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    We report on the influence of the improved L2(1) ordering degree on the magnetic properties of Co2MnSi Heusler films. Different fractions of the L2(1) phase are obtained by different postgrowth annealing temperatures ranging from 350 degrees C to 500 degrees C. Room temperature magneto-optical Kerr effect measurements reveal an increase of the coercivity at an intermediate annealing temperature of 425 degrees C. This is probably a result of an increasing number of pinning centers on the one hand and a drop of the cubic anisotropy constant K-1 by a factor of 10 on the other for an increasing amount of the L2(1) phase. Furthermore, Brillouin light scattering studies show that the improvement of the L2(1) order in the Co2MnSi films is correlated with a decrease of the saturation magnetization by about 7%. The exchange stiffness constant of Co2MnSi, however, increases by about 8% when the L2(1) order is improved. (C) 2008 American Institute of Physics.

  232. Tunneling magnetoresistance of magnetic tunnel junctions using perpendicular magnetization L1(0)-CoPt electrodes 査読有り

    Gukcheon Kim, Yuya Sakuraba, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS LETTERS 92 (17) 2008年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2913163  

    ISSN:0003-6951

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    Magnetic tunnel junctions (MTJs) using L1(0)-ordered CoPt electrodes with perpendicular magnetic anisotropy were fabricated. Full-epitaxial CoPt/MgO/CoPt-MTJs were prepared onto single crystal MgO-(001) substrate by sputtering method. X-ray diffraction analyses revealed that both bottom and top CoPt electrodes were epitaxially grown with (001)-orientation. The L1(0)-chemical order parameter of 0.82 was obtained for the bottom CoPt electrode deposited at substrate temperature of 600 degrees C. The transport measurements with applying magnetic field perpendicular to the film plane showed a tunnel magnetoresistance ratio of 6% at room temperature and 13% at 10 K. (C) 2008 American Institute of Physics.

  233. Magnetic second harmonic generation at the Co2MnSi/AlOx interface 査読有り

    L. R. Shelford, Y. Liu, R. J. Hicken, Y. Sakuraba, M. Oogane, Y. Ando

    JOURNAL OF APPLIED PHYSICS 103 (7) 2008年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2841174  

    ISSN:0021-8979

    eISSN:1089-7550

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    We have studied magnetic second harmonic generation (MSHG) at the Co2MnSi/AlOx interface. The variation of the MSHG intensity was consistent with the nonvanishing components of the nonlinear susceptibility tensor expected for the (001) cubic surface. The difference in the MSHG asymmetry, the MSHG anisotropy, is found to have maximum value at an annealing temperature of 450 degrees C, for which similar samples have previously been found to show optimum L2(1) site ordering and maximum tunnel magnetoresistance. (C) 2008 American Institute of Physics.

  234. Tunnel magnetoresistance effect in magnetic tunnel junctions using a Co2MnSi(110) electrode 査読有り

    Masashi Hattori, Yuya Sakuraba, Mikihiko Oogane, Yasuo Ando, Terunobu Miyazaki

    APPLIED PHYSICS EXPRESS 1 (2) 2008年2月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.1.021301  

    ISSN:1882-0778

    eISSN:1882-0786

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    Magnetic tunnel junctions (MTJs) with half-metallic electrodes are expected to show a large tunnel magnetoresistance (TMR) ratio, according to Julliere's model. A Co2MnSi Heusler alloy is theoretically expected to possess a half-metallic electronic state. Experimentally, at low temperature, Co2MnSi(100)/Al-oxide/CoFe junctions exhibited a large TMR ratio. We fabricated MTJs with high-quality (110)oriented Co2MnSi electrodes and investigated the TMR effects. We obtained a TMR ratio of about 40% at room temperature and 120% at 2 K, respectively. However, we observed degradation of the energy gap Of Co2MnSi in the minority spin band from the conductance-voltage characteristics. We infer that the interface of Co2MnSi(110) possesses no half-metallic property. (c) 2008 The Japan Society of Applied Physics.

  235. スピントロニクスの形成と発展 招待有り 査読有り

    宮﨑照宣, 大兼幹彦, 桜庭裕弥, 渡邉大輔, R. Yilgin, 佐久間昭正, 安藤康夫, 久保田均

    粉体および粉末治金 55 (2) 109-115 2008年2月

    DOI: 10.2497/jjspm.55.109  

    ISSN:0532-8799

  236. Nonquasiparticle states in Co2MnSi evidenced through magnetic tunnel junction spectroscopy measurements 査読有り

    L. Chioncel, Y. Sakuraba, E. Arrigoni, M. I. Katsnelson, M. Oogane, Y. Ando, T. Miyazaki, E. Burzo, A. I. Lichtenstein

    PHYSICAL REVIEW LETTERS 100 (8) 2008年2月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.100.086402  

    ISSN:0031-9007

    eISSN:1079-7114

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    We investigate the effects of electronic correlations in the full-Heusler Co2MnSi, by combining a theoretical analysis of the spin-resolved density of states with tunneling-conductance spectroscopy measurements using Co2MnSi as electrode. Both experimental and theoretical results confirm the existence of so-called nonquasiparticle states and their crucial contribution to the finite-temperature spin polarization in this material.

  237. Lower-current and Fast switching of A Perpendicular TMR for High Speed and High density Spin-Transfer-Torque MRAM 査読有り

    Kishi T, Yoda H, Kai T, Nagase T, Kitagawa E, Yoshikawa M, Nishiyama K, Daibou T, Nagamine M, Amano M, Takahashi S, Nakayama M, Shimomura N, Aikawa H, Ikegawa S, Yuasa S, Yakushiji K, Kubota H, Fukushima A, Oogane M, Miyazaki T, Ando K, IEEE

    Ieee International Electron Devices Meeting 2008, Technical Digest 309-+ 2008年

  238. Gilbert Damping for Various Ni<SUB>80</SUB>Fe<SUB>20</SUB> Thin Films Investigated Using All-Optical Pump-Probe Detection and Ferromagnetic Resonance, 査読有り

    S. Mizukami, H. Abe, D. Watanabe, M. Oogane, Y. Ando, T. Miyazaki

    Appl. Phys. Exp 1 (12) 121301-1-121301-3 2008年

    出版者・発行元:Japan Society of Applied Physics

    DOI: 10.1143/APEX.1.121301  

    ISSN:1882-0778

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    All-optical pump--probe detection of magnetization precession has been performed to investigate Gilbert damping in several types of Ni80Fe20 films. The frequency and decay time of magnetization precession depended on pump fluence. At low pump fluence, Gilbert damping constants, derived from the magnetic field dependence on frequency and decay time of magnetization precession, were identical to values obtained from X-band ferromagnetic resonance within the experimental errors.

  239. TMR素子を用いた高感度地磁気センサーの開発 査読有り

    高太好, 大兼幹彦, 安藤康夫

    日本磁気学会誌 32 (3) 361-365 2008年

    出版者・発行元:公益社団法人日本磁気学会

    DOI: 10.3379/msjmag.32.361  

    ISSN:1882-2924

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    The TMR (<u>T</u>unneling <u>M</u>agneto-<u>r</u>esistive) junctions of SiO<sub>2</sub>-sub./bottom-electrode/IrMn/CoFe/Al-oxide/NiFe/ top-electrode were fabricated. We have succeeded to observe both high sensitivity and linearity in a low magnetic field for the optimized TMR junctions. The circuit of magnetic sensor using developed TMR junctions exhibited high output signal enough to resolve over 36 directions at terrestrial magnetism. The terrestrial sensor using TMR junctions is very small size and low energy consumption, so will be key "tools" for some solutions, for example, a navigation sensor with Global Positioning System(GPS) in cell phones.

  240. Study of a Spin Torque Transfer MRAM with Perpendicular Magnetization TMR Elements as a High Density Non-volatile Memory 査読有り

    H. Yoda, M. Oogane

    Electrochem. Soc 2008年

  241. CoFeB/MgO/CoFeBトンネル接合のナノ秒領域におけるスピン注入磁化反転と実時間測定 査読有り

    青木 達也, 大兼 幹彦, 宮崎 照宣, 安藤 康夫

    Journal of the Magnetics Society of Japan 32 (3) 355-360 2008年

    出版者・発行元:公益社団法人日本磁気学会

    DOI: 10.3379/msjmag.32.355  

    ISSN:1882-2924

    詳細を見る 詳細を閉じる

    Detailed spin-transfer switching (STS) properties in the nanosecond regime were investigated. We prepared a CoFeB/MgO/CoFeB magnetic tunnel junction that exhibits a 115 % magnetoresistance ratio. The STS property in the ≥ 2 ns region was obtained by static measurement. We then examined this property from several points of view. In addition, we outlined a new method of real-time switching observation. That is expected to clarify the STS mechanism directly. Using this method, the contribution of the thermal activation effect in a switching current below <i>I</i><sub>C0</sub> was successfully detected. This indicates that the real-time method has the advantage that it clarifies the STS mechanism.

  242. 高配向Nd2Fe14B薄膜のX線回折と磁気特性 査読有り

    小川 大介, 秋屋 貴博, 大兼 幹彦, 安藤 康夫, 加藤 宏朗

    Journal of the Magnetics Society of Japan 32 (6) 548-553 2008年

    出版者・発行元:公益社団法人日本磁気学会

    DOI: 10.3379/msjmag.32.548  

    ISSN:1882-2924

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    Nd<sub>2</sub>Fe<sub>14</sub>B thin films were fabricated with a DC magnetron sputtering system. X-ray diffraction experiments and the Rietveld analysis showd that the crystallites of the Nd<sub>2</sub>Fe<sub>14</sub>B phase were highly oriented perpendicular to the film plane. In addition to the diffraction peaks originated from the Nd<sub>2</sub>Fe<sub>14</sub>B phase, we observed extra reflections that can be assigned as a NdO phase. The relative intensity, hence the volume fraction of the NdO phase varied depending on the sputtering conditions such as the substrate temperature, Ar gas pressure, and Ta buffer layer thickness. It was found that the magnetization value depends strongly on the Ar gas pressure and reaches a maximum at 0.7 Pa of Ar gas pressure. The maximum magnetization value is 15 kG, which is comparable with the bulk value. The optimized values of the maximum energy product, saturation magnetization, and coercivity are (<i>BH</i>)<sub>max</sub> = 36 MGOe, 4π<i>M</i><sub>s</sub> = 14.7 kG, and <i>H</i><sub>c</sub> = 6.7 kOe, respectively.

  243. Ultrafast optical modification of magnetic anisotropy and stimulated precession in an epitaxial Co2MnAl thin film 査読有り

    Y. Liu, L. R. Shelford, V. V. Kruglyak, R. J. Hicken, Y. Sakuraba, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF APPLIED PHYSICS 101 (9) 2007年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2711702  

    ISSN:0021-8979

    eISSN:1089-7550

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    An all-optical pump-probe method was used to study magnetization precession in an epitaxial Co2MnAl Heusler alloy thin film. The frequency and amplitude of precession showed a clear fourfold variation as the orientation of the static field was applied in different directions within the plane of the film, revealing that the precession is induced by an ultrafast modification of the magnetocrystalline anisotropy field. The effective fields acting upon the magnetization have been determined and the damping parameter is found to decrease rapidly as the strength of the applied field is increased.

  244. New magnetic nanodot memory with FePt nanodots 査読有り

    Cheng-Kuan Yin, Mariappan Murugesan, Ji-Chel Bea, Mikihiko Oogane, Takafumi Fukushima, Tetsu Tanaka, Shozo Kono, Seiji Samukawa, Mitsumasa Koyanagi

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (4B) 2167-2171 2007年4月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.46.2167  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    A new magnetic nanodot (MND) memory with FePt nanodots was proposed. The FePt nanodots dispersed in SiO2 insulating film was successfully fabricated by self-assembled nanodot deposition (SAND). The size of the FePt nanodot can be controlled by SAND with a different target area ratio of the FePt pellets area in the SiO2 target. Thermal annealing converts the magnetic properties of the FePt nanodots from anti ferrom agnetic into high coercivity ferromagnetic without thermal agglomeration. An L1(0) face-centered tetragonal (fct) FePt MND film was successfully formed which acted as a charge retention layer. Furthermore, the fundamental characteristics of the MND memory were investigated-Using magnetic metal oxide semiconductor (MOS) capacitor devices.

  245. Half-metallic band structure observed in Co2MnSi-based magnetic tunnel junctions 査読有り

    Y. Sakuraba, M. Hattori, M. Oogane, H. Kubota, Y. Ando, A. Sakuma, T. Miyazaki

    Journal of Physics D: Applied Physics 40 (5) 1221-1227 2007年3月7日

    DOI: 10.1088/0022-3727/40/5/S02  

    ISSN:0022-3727 1361-6463

    詳細を見る 詳細を閉じる

    Magnetic tunnel junctions (MTJs) with stacking structures of Co 2MnSi/Al-O/CoFe and Co2MnSi/Al-O/Co2MnSi were fabricated using a magnetron sputtering system. Co2MnSi/Al-O/CoFe-MTJ and Co2MnSi/Al-O/Co2MnSi-MTJ exhibited extremely large tunnelling magnetoresistance ratios of 159% and 570%, respectively, at low temperature, indicating the half-metallicity of Co2MnSi. We investigated the bias voltage dependence of tunnelling conductance (dI/dV-V) for each MTJ in order to clarify the band structure around the Fermi level in Co2MnSi. The observed dI/dV-V curves for both MTJs reveal a clear half-metallic energy gap at 350-400 meV for Co2MnSi, with an energy separation of just 10 meV between the Fermi energy and the bottom edge of the conduction band. © 2007 IOP Publishing Ltd.

  246. Gilbert damping constant in polycrystalline CO2MnSi Heusler alloy films 査読有り

    R. Yilgin, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 2322-2323 2007年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.11.032  

    ISSN:0304-8853

    詳細を見る 詳細を閉じる

    The Gilbert damping constant was investigated in polycrystalline Co2MnSi Heusler alloy thin films by ferromagnetic resonance ( FMR) technique. Samples were prepared using the magnetron sputtering technique on SiO2 substrate and annealed at various temperatures to control the structure. The intrinsic Gilbert damping constant was obtained from angular dependences of peak- to- peak line widths fitting from FMR spectra using Landau - Lifshitz - Gilbert equation. Intrinsic damping constants of the polycrystalline Co2MnSi films were almost independent of the annealing temperature. (c) 2006 Elsevier B. V. All rights reserved.

  247. Boron effects on noise in magnetic tunnel junctions 査読有り

    A. F. Md Nor, T. Daibou, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 1917-1919 2007年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.10.1126  

    ISSN:0304-8853

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    Normalized noise at different boron atomic percentages varying from 20%, 25%, and 30% was shown to increase with increasing boron content. The TMR% of the junction with 30% boron content shows almost 0% TMR. The X- ray diffraction patterns on these junctions, suggesting that the degree of crystallinity in MgO with increasing boron content, have deteriorated. Thus, high crystallinity is not only a vital factor for obtaining a high TMR ratio but also serve as a facilitating condition for lower noise. (c) 2006 Elsevier B. V. All rights reserved.

  248. Bias voltage dependence of tunnel magnetoresistance effect in CoFeB/MgO/Co2X(X = Fe, Mn)Si magnetic tunnel junctions 査読有り

    T. Daibou, M. Shinano, M. Hattori, Y. Sakuraba, M. Oogane, Y. Ando, T. Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 1926-1928 2007年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.10.761  

    ISSN:0304-8853

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    Magnetic tunnel junctions ( MTJs) with structure of sub ( thermal oxidized Si)/ Ta( 10 nm)/ Py( 2 nm)/ IrMn( 10 nm)/ Co75Fe25( 2 nm)/ Ru( 0.85 nm)/ Co40Fe40B20( 5 nm)/ MgO( 2.5 nm)/ poly crystalline Co2FeSi or Co2MnSi Heusler alloys/ Ta( 7)/ Ru( 7) have been grown by magnetron sputtering method. Differential resistance ( dV/ dI) and bias voltage dependence of the TMR ratio have been investigated at 6K. The shape of TMR- V curve for the MTJ with Co2MnSi showed significant voltage dependence of the TMR ratio. (c) 2006 Elsevier B. V. All rights reserved.

  249. Tunneling Spin Polarization and Magnetic Properties of Co–Fe–B Alloys and Their Dependence on Boron Content 査読有り

    T. Kubota, T. Daibou, M. Oogane, Y. Ando, T. Miyazaki

    Jpn. J. Appl. Phys. 46 (8-11) L250-L252 2007年3月

    出版者・発行元:None

    DOI: 10.1143/JJAP.46.L250  

    ISSN:0021-4922

  250. Co2MnSiを用いた強磁性トンネル接合における極高スピン分極率の実現 査読有り

    桜庭 裕弥, 服部正志, 大兼 幹彦, 久保田 均, 安藤 康夫, 宮﨑 照宣

    日本応用磁気学会誌 31 (4) 338-343 2007年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.31.338  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    We fabricated Co<sub>2</sub>MnSi/(Mg)/Al-O/CoFe MTJs using UHV magnetron sputtering. The interfacial chemical bond between Co<sub>2</sub>MnSi and Al-O was intensively optimized by changing plasma oxidation time for Al-O and by inserting a Mg layer. The Mg inserted layer between Co<sub>2</sub>MnSi and Al-O effectively suppressed the generation of interfacial magnetic impurities. Finally, we successfully observed a giant TMR ratio of 203% at 2 K in the MTJ with a 1.0 nm-Mg layer inserted. The spin-polarization for Co<sub>2</sub>MnSi estimated from this TMR ratio was 0.97-1.00, which indicated that an almost perfect spin-polarized state was achieved. We also investigated the relationship between the TMR ratio and the site-ordering level of Co<sub>2</sub>MnSi. As a result, we found that an <i>L</i>2<sub>1</sub>-ordering state is not necessary to achieve high spin-polarization for Co<sub>2</sub>MnSi in MTJs.

  251. Interfacial structure and half-metallic ferromagnetism in Co2MnSi-based magnetic tunnel junctions 査読有り

    N. D. Telling, P. S. Keatley, G. van der Laan, R. J. Hicken, E. Arenholz, Y. Sakuraba, M. Oogane, Y. Ando, T. Miyazaki

    PHYSICAL REVIEW B 74 (22) 2006年12月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.74.224439  

    ISSN:2469-9950

    eISSN:2469-9969

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    X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) techniques are utilized to explore the ferromagnetic/barrier interface in Co2MnSi full Heusler alloy magnetic tunnel junctions. Structural and magnetic properties of the interface region are studied as a function of the degree of site disorder in the alloy and for different degrees of barrier oxidation. Photoelectron scattering features that depend upon the degree of L2(1) ordering are observed in the XAS spectra. Additionally, the moments per 3d hole for Co and Mn atoms are found to be a sensitive function of both the degree of L2(1) ordering and the barrier oxidation state. Significantly, a multiplet structure is observed in the XMCD spectra that indicates a degree of localization of the moments and may result from the half-metallic ferromagnetism (HMF) in the alloy. The magnitude of this multiplet structure appears to vary with preparation conditions and could be utilized to ascertain the role of the constituent atoms in producing the HMF, and to examine methods for preserving the half-metallic state after barrier preparation. The changes in the magnetic structure caused by barrier oxidation could be reversed by inserting a thin Mg interface layer in order to suppress the oxidation of Mn in the Co2MnSi layer.

  252. Tunnel magnetoresistance effect in CoFeB/MgO/Co2FeSi and Co2MnSi tunnel junctions 査読有り

    T. Daibou, M. Shinano, M. Hattori, Y. Sakuraba, M. Oogane, Y. Ando, T. Miyazaki

    IEEE TRANSACTIONS ON MAGNETICS 42 (10) 2655-2657 2006年10月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2006.879733  

    ISSN:0018-9464

    eISSN:1941-0069

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    We have fabricated MgO-based magnetic tunnel junctions (MTJs) with the CoFeB bottom electrode and top electrodes of poly crystaline Co2FeSi and Co-2 MnSi Heusler alloys. We have measured temperature dependence of the TMR ratio and TMR-V characteristics at 6 K. We have achieved a high TMR ratio of 90 % at RT for the MTJ with Co-2 FeSi electrode after annealing at 325 degrees C. The MTJ with Co-2 MnSi electrode showed a significant annealing temperature dependence of the TMR ratio. The increase of TMR ratio by annealing is due to the crystallization of the Co-2 MnSi Hensler layer. Furthermore, the strong temperature dependence of TMR ratio and the anomalous TMR-V characteristics have been observed in the MTJ with Co2MnSi.

  253. Direct observation of half-metallic energy gap in Co2MnSi by tunneling conductance spectroscopy 査読有り

    Y. Sakuraba, T. Miyakoshi, M. Oogane, Y. Ando, A. Sakuma, T. Miyazaki, H. Kubota

    APPLIED PHYSICS LETTERS 89 (5) 052508 2006年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2335583  

    ISSN:0003-6951

    eISSN:1077-3118

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    Magnetic tunnel junctions with a Co2MnSi/Al-O/CoFe structure are prepared by magnetron sputtering and investigated with respect to the energy gap near the Fermi energy level. The plasma oxidation time for the Al-O barrier is found to affect the condition of the Co2MnSi/Al-O interface. The optimized sample (50 s oxidation time) exhibits a magnetoresistance ratio of 159% and tunneling spin polarization of 0.89 at 2 K. The bias voltage dependence of tunneling conductance (dI/dV-V) reveals a clear half-metallic energy gap at 350-400 meV for Co2MnSi, with an energy separation of just 10 meV between the Fermi energy and the bottom edge of conduction band. (c) 2006 American Institute of Physics.

  254. Magnetic damping in ferromagnetic thin films 査読有り

    Mikihiko Oogane, Takeshi Wakitani, Satoshi Yakata, Resul Yilgin, Yasuo Ando, Akimasa Sakuma, Terunobu Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (5A) 3889-3891 2006年5月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.45.3889  

    ISSN:0021-4922

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    We determined the Gilbert damping constants of Fe-Co-Ni and Co-Fe-B alloys with various compositions and half-metallic Co2MnAl Heusler alloy films prepared by magnetron sputtering. The ferromagnetic resonance (FMR) technique was used to determine the damping constants of the prepared films. The out-of-plane angular dependences of the resonance field (H-R) and line width (Delta H-pp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The experimental results fitted well, considering the inhomogeneities of the films in the fitting. The damping constants of the where metallic films were much larger than those of bulk ferrimagnetic insulators and were roughly proportional to (g - 2)(2), is the Lande g factor. We discuss the origin of magnetic damping, considering spin-orbit and s-d interactions.

  255. Giant tunneling magnetoresistance in Co2MnSi/Al-O/Co2MnSi magnetic tunnel junctions 査読有り

    Y. Sakuraba, M. Hattori, M. Oogane, Y. Ando, H. Kato, A. Sakuma, T. Miyazaki, H. Kubota

    APPLIED PHYSICS LETTERS 88 (19) 192508 2006年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2202724  

    ISSN:0003-6951

    eISSN:1077-3118

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    Magnetic tunnel junctions (MTJs) with a stacking structure of Co2MnSi/Al-O/Co2MnSi were fabricated using magnetron sputtering system. Fabricated MTJ exhibited an extremely large tunneling magnetoresistance (TMR) ratio of 570% at low temperature, which is the highest TMR ratio reported to date for an amorphous Al-O tunneling barrier. The observed dependence of tunneling conductance on bias voltage clearly reveals the half-metallic energy gap of Co2MnSi. The origins of large temperature dependence of TMR ratio were discussed on the basis of the present results.(c) 2006 American Institute of Physics.

  256. Fabrication and evaluation of magnetic tunnel junction with MgO tunneling barrier 査読有り

    Takeshi Sakaguchi Hoon Choi, Ahn Sung-Jin, Takeaki Sugimura, Mungi Park, Milcihiko Oogane, Hyuckjae Oh, Jun Hayakawa, Shoji Ikeda, Young Min Lee, Takafumi Fukushima, Terunobu Miyazaki, Hideo Ohno, Mitsumasa Koyanagi

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (4B) 3228-3232 2006年4月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.45.3228  

    ISSN:0021-4922

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    Magnetoresistive random access' memory (MRAM) has recently attracted considerable attention due to its non-volatility and high programming speed. A high Tunnel magnetoresistance (TMR) ratio is a key factor of MRAM. However, a conventional MRAM using aluminum oxide as insulator film shows a low TMR ratio of several tens of percents. MgO tunneling insulator is one of the candidates for achieving a high TMR ratio. In this study, we fabricated and evaluated Magnetic tunnel junctions (MTJs) with MgO tunneling barrier on a clad Cu word line.

  257. Tunneling spectroscopy in CoFeB/MgO/CoFeB magnetic tunnel junctions 査読有り

    K Ono, T Daibou, SJ Ahn, Y Sakuraba, T Miyakoshi, T Morita, Y Kikuchi, M Oogane, Y Ando, T Miyazaki

    JOURNAL OF APPLIED PHYSICS 99 (8) 2006年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2173628  

    ISSN:0021-8979

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    The d(2)V/dI(2)-V measurements were used to investigate the tunneling mechanism in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), which showed a giant tunnel magnetoresistance ratio up to 200% at room temperature. The d(2)V/dI(2)-V spectra of CoFeB/MgO/CoFeB junctions resemble those of single-crystal Fe(001)/MgO(001)/Fe(001) MTJs. Broad peaks appeared around +/- 600 mV in spectra for antiparallel magnetic configurations. A complex structure was apparent in the spectra for parallel configurations. We inferred that giant tunnel magnetoresistance observed in CoFeB/MgO/CoFeB junctions originates in coherent tunneling between the Delta(1) bands of crystallized CoFeB electrodes. (C) 2006 American Institute of Physics.

  258. Large tunnel magnetoresistance in magnetic tunnel junctions using Co 2MnX (X ≤ Al, Si) Heusler alloys 招待有り 査読有り

    M. Oogane, Y. Sakuraba, J. Nakata, H. Kubota, Y. Ando, A. Sakuma, T. Miyazaki

    Journal of Physics D: Applied Physics 39 (5) 834-841 2006年3月7日

    DOI: 10.1088/0022-3727/39/5/S09  

    ISSN:0022-3727

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    We fabricated B2-ordered Co2MnAl and L21-ordered Co2MnSi Heusler alloy films by optimizing various fabrication conditions (substrate, composition of sputtering target, substrate and post-annealing temperature, etc) and applied these films to bottom electrodes of magnetic tunnel junctions (MTJs). We used Al-oxide insulating tunnel barriers for our MTJs and varied oxidation times of Al films to control qualities of the Al-oxide insulating layer and Heusler-alloy/Al-oxide interface. Observed tunnel magnetoresistance (TMR) ratios were extremely sensitive to the structure and surface morphology of the prepared Heusler alloy films. Epitaxially grown Heusler alloy films showed good structural quality, very flat surfaces and enhanced TMR ratios. The behaviour of the TMR ratios towards oxidation time for the preparation of the Al-oxide barriers and the measurement temperature dependence of the TMR ratios were quite different between the MTJs with Co 2MnAl and Co2MnSi electrodes. The obtained TMR ratio of 83% at 2 K in the MTJ with epitaxially grown B2-ordered Co2MnAl was large among the MTJs with an amorphous Al-oxide tunnel barrier. This result suggests that B2-ordered Co2MnAl is a highly spin-polarized material, as predicted by our theoretical calculation. Moreover, we observed a very large TMR ratio of 159% at 2 K in the MTJ with a high-quality epitaxially grown L21-ordered Co2MnSi electrode. This TMR ratio is the highest value to date in MTJs using an amorphous Al-oxide tunnel barrier. Spin-polarization of the Co2MnSi bottom electrode obtained from Julliere's formula was about 0.89. This value is also the largest achieved to date for a Heusler material and is much larger than those of conventional ferromagnetic materials such as Co-Fe. This large spin-polarization is attributed to a half-metallic band structure, as predicted by theoretical calculations. © 2006 IOP Publishing Ltd.

  259. Low-frequency noise in MgO magnetic tunnel junctions 査読有り

    A. F. M. Nor, T. Kato, S. J. Ahn, T. Daibou, K. Ono, M. Oogane, Y. Ando, T. Miyazaki

    J. Appl. Phys. 99 08T306-1-08T306-3 2006年

    DOI: 10.1063/1.2165142  

  260. FMRを用いた強磁性金属中におけるスピン拡散長の測定 査読有り

    家形諭, 安藤康夫, 大兼幹彦, 宮崎照宣

    日本応用磁気学会誌 31 2006年

  261. Fabrication of Co2MnAl Heusler Alloy Epitaxial Film Using Cr Buffer Layer 査読有り

    Y. Sakuraba, J. Nakata, M. Oogane, H. Kubota, Y. Ando, A. Sakuma, T. Miyazaki

    Jpn. J. Appl. Phys. 44 2006年

    DOI: 10.1143/JJAP.44.6535  

  262. Magnetic tunnel junctions using B2-ordered Co2MnAl Heusler alloy epitaxial electrode 査読有り

    Y Sakuraba, J Nakata, M Oogane, Y Ando, H Kato, A Sakuma, T Miyazaki, H Kubota

    APPLIED PHYSICS LETTERS 88 (2) 022503 2006年1月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2162867  

    ISSN:0003-6951

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    Magnetic tunnel junctions were fabricated with epitaxially grown Co2MnAl bottom electrodes combined with an Al-O tunnel barrier using a magnetron sputtering system. The epitaxial Co2MnAl electrode had very low surface roughness of 0.2 nm and a highly ordered B2 structure. Magnetic tunnel junctions (MTJs) with a stacking structure of epitaxial-Co2MnAl/Al-O/CoFe/IrMn exhibited large tunnel magnetoresistance (TMR) ratios of 65% at room temperature and 83% at 10 K. The TMR ratios were larger than those of a MTJ with a Co2MnAl polycrystalline electrode.

  263. Low frequency noise in CoFeB/MgO(100)/CoFeB magnetic tunnel junctions 査読有り

    A. F. Md Nor, T. Daibou, M. Oogane, Y. Ando, T. Miyazaki

    INTERMAG 2006 - IEEE International Magnetics Conference 858 2006年

    DOI: 10.1109/INTMAG.2006.374889  

  264. Anisotropic Intrinsic Damping Constant in Epitaxial Co2MnSi Heusler Alloy Films 査読有り

    R. Yilgin, Y. Sakuraba, M. Oogane, S. Mizukami, Y. Ando, T. Miyazaki

    Jpn. J. Appl. Phys. 46 (9) L205-L208 2006年

    出版者・発行元:Japan Society of Applied Physics

    DOI: 10.1143/JJAP.46.L205  

    ISSN:0021-4922

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    We investigated the Gilbert damping constant of the Heusler Co2MnSi(001) films epitaxially grown on a MgO(100) substrate by a ferromagnetic resonance technique. The angular variation in resonance field in the in-plane geometry exhibited a maximum when the field was applied parallel to the [110] direction (easy axis), and its relative minimum corresponded to the $\mathrm{H}\parallel[100]$ hard axis. Experimental results were fitted with theoretical results; the $g$-value, effective magnetization and anisotropy constants were determined. The magneto-crystalline anisotropy of the films decreased after the films were post-annealed at 400 °C. The Gilbert damping parameter was anisotropic and had a minimum value at 300 °C.

  265. Gilbert Damping Constants of Co2FeSi Heusler Alloy Film 査読有り

    M. Oogane, R. Yilgin, S. Shinano, S. Yakata, H. Kubota, Y. Ando, T. Miyazaki

    J. Appl. Phys. 2006年

  266. コプレーナ伝送路を有する微小強磁性トンネル接合の作製 査読有り

    青木達也, 渡邉大輔, 大坊忠臣, 安藤康夫, 大兼幹彦, 宮﨑照宣

    日本応用磁気学会誌 31 (2) 94-97 2006年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.31.94  

    ISSN:0285-0192

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    Investigation of current induced magnetization switching properties in nanosecond regime in ferromagnetic tunnel junctions is increasing its necessity for realization of fast operating magnetic random access memory (MRAM). In this work, appropriate electrode structures for such a measurement were investigated. The electrode structure was designed as a typical coplanar waveguide with 50Ω characteristic impedance (structure A). Although the buffer layer thickness and the distance between the signal line and the ground line were altered, the large frequency dependenceof the insertion loss was not improved. The revised structure (structure B) with small cross section area between the signal line and the ground line showed very flat transmission properties over 20 GHz. Consequently, submicron sized Ta/FeNi/IrMn/CoFe/Ru/CoFeB/MgO/CoFeB/Ta/Ru ferromagnetic tunnel junctions with the electrodes of structure Bwere fabricated. The tunnel magnetoresistance ratio was 108 % after annealing at 250 °C.

  267. Co2MnSi (110)ホイスラー合金を用いたトンネル接合における磁気抵抗効果 査読有り

    服部正志, 桜庭裕弥, 大兼 幹彦, 安藤 康夫, 宮﨑 照宣

    日本応用磁気学会誌 2006年

  268. CoFeB合金薄膜の磁気緩和定数測定 査読有り

    大兼 幹彦, 渡邉 美穂, 家形 諭, 安藤 康夫, 宮﨑 照宣

    日本応用磁気学会誌 2006年

  269. Intrinsic Gilbert damping constant in CO2MnAl Heusler alloy films 査読有り

    R Yilgin, M Oogane, S Yakata, Y Ando, T Miyazaki

    IEEE TRANSACTIONS ON MAGNETICS 41 (10) 2799-2801 2005年10月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2005.854832  

    ISSN:0018-9464

    eISSN:1941-0069

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    Intrinsic alpha-damping constants of CO2MnAl Hensler alloy films prepared by magnetron sputtering were investigated. After deposition of Co2MnAl films, the films were annealed at 200-400 degrees C to control the crystal structure and the atomic order between Co, Mn, and Al sites. Ferromagnetic resonance (FMR) technique was used to obtain alpha values of Co2MnAl films in this study. Out-of-plane angular dependences of the resonance field (H-R) and linewidth (Delta H-pp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The authors were able to fit all experimental results well because of the lack of inhomogeneities in prepared Co-2 MnAl films. The alpha-damping constants obtained from the fitting results decreased with increasing annealing temperature and showed a minimum value of 0.007 at 300 degrees C. It was found that a degree of B2 structure order can sensitively affect alpha-damping constants of Co2MnAl films.

  270. Spin-dependent tunneling spectroscopy in single-crystal Fe/MgO/Fe tunnel junctions 査読有り

    Y Ando, T Miyakoshi, M Oogane, T Miyazaki, H Kubota, K Ando, S Yuasa

    APPLIED PHYSICS LETTERS 87 (14) 2005年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2077861  

    ISSN:0003-6951

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    We report a detailed spin-dependent tunneling spectroscopy in single-crystal Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) that show a giant tunnel magnetoresistance effect. Spectra for antiparallel magnetic configurations show asymmetry because of extrinsic electron scatterings caused by structural defects at the barrier/electrode interfaces. Surprisingly, spectra for parallel magnetic configurations exhibit a complex oscillatory structure that has never been observed in conventional MTJs with an aluminum-oxide tunnel barrier. The complex spectra reflect the tunneling process via interface resonant states. These results provide some information that helps to elucidate the physics of spin-dependent electron tunneling and to further enhance magnetoresistance. (C) 2005 American Institute of Physics.

  271. Fabrication and Evaluation of Magnetic Tunnel Junction with MgO Tunneling Barrier 査読有り

    Takeshi Sakaguchi, Hoon Choi, Takeaki Sugimura, Mikihiko Oogane, Hyuckjae Oh, Jun Hayakawa, Shoji Ikeda, Young Min Lee, Takafumi Fukushima, Terunobu Miyazaki, Hideo Ohno, Mitsumasa Koyanagi

    International Conference on Solid State Device and Materials (SSDM) 2005 642-643 2005年9月

  272. Fabrication and characterization of Co–Mn–Al Heusler-type thin film 査読有り

    H. Kubota, J. Nakata, M. Oogane, Y. Ando, H. Kato, A. Sakuma, T. Miyazaki

    JOURNAL OF APPLIED PHYSICS 97 (10) 2005年5月

    出版者・発行元:None

    DOI: 10.1063/1.1852329  

    ISSN:0021-8979

    eISSN:1089-7550

  273. Huge spin-polarization of L2(1)-ordered Co2MnSi epitaxial Heusler alloy film 査読有り

    Y Sakuraba, J Nakata, M Oogane, H Kubota, Y Ando, A Sakuma, T Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 (33-36) L1100-L1102 2005年

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.44.L1100  

    ISSN:0021-4922

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    Magnetic tunnel junctions (MTJs) with a stacking structure of epitaxial CO2MnSi/Al-O barrier/poly-crystalline CO75Fe25 were fabricated using an ultrahigh vacuum sputtering system. The epitaxial CO2MnSi bottom electrode exhibited highly ordered L2(1) structure and very smooth surface morphology. Observed magnetoresistance (MR) ratios of 70% at room temperature (RT) and 159% at 2 K are the highest values to date for MTJs using a Heusler alloy electrode. A high spin-polarization of 0.89 at 2 K for CO2MnSi obtained from Julliere's model coincided with the half-metallic band structure that was predicted by theoretical calculations.

  274. Temperature dependence of tunnel magnetoresistance in Co-Mn-Al/Al-oxide/Co-Fe junctions 査読有り

    M Oogane, J Nakata, H Kubota, Y Ando, A Sakuma, T Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 (24-27) L760-L762 2005年

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.44.L760  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    We investigated the temperature dependence of the tunnel magnetoresistance (TMR) effect in Co-Mn-Al/Al-oxide/Co-Fe tunnel junctions. The junction prepared without exposure to air during deposition showed very large TMR ratios of 65% at 10 K and 40% at room temperature. In contrast, the junction prepared with air exposure before and after Al-oxide layer fabrication showed a maximum TMR ratio of only 40% at a low temperature. Temperature dependences of tunnel conductance of these junctions were analyzed using a simple model that incorporates two contributions: elastic tunneling with decreasing spin polarization as temperature increases and spin- independent hopping tunneling through trap states in Al-oxide tunnel barriers. Results of analyses indicated that air exposure drastically reduced spin polarization and Curie temperature. It also created an inferior insulating layer at the Co-Mn-Al/Al-oxide interface.

  275. Spin-dependent inelastic electron tunneling spectroscopy of magnetic tunnel junctions 査読有り

    M Hayashi, Y Ando, M Oogane, H Kubota, T Miyazaki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (11A) 7472-7476 2004年11月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.43.7472  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    We investigated the nature of spin dependent scattering by employing inelastic electron tunneling spectroscopy in magnetic tunnel junctions. In this work we introduced a comparable quantity represented as (d(2)V/dI(2))/(dV/dI) by simultaneous measurements of the dV/dI and d(2)V/dI(2) curves. In each junction we measured, a zero bias anomaly was observed close to the Fermi energy (+/-2 mV). Furthermore, a relatively large spin dependent scattering occurred around 18 mV. These peaks and zero bias anomalies were the primary cause of the drop of the tunneling magnetoresistance (TMR) ratio as the bias voltage was applied. Furthermore, insertion of a normal metal between the insulator and ferromagnetic metal was examined. Silver exhibited a reduction of spin dependent scattering, while excess aluminum induced a large zero bias anomaly.

  276. Tunnel Conductance in Ni80Fe20/Al-oxide/Al Junctions below the Superconducting Temperature of Al Films 査読有り

    M. Oogane, T. Daibou, H. Kubota, Y. Ando, T. Miyazaki

    Transactions of Magnetic Research Society of Japan 2004年8月

  277. Large magnetoresistance in magnetic tunnel junctions using Co-Mn-Al full heusler alloy 査読有り

    Hitoshi Kubota, Jun Nakata, Mikihiko Oogane, Yasuo Ando, Akimasa Sakuma, Terunobu Miyazaki

    Japanese Journal of Applied Physics, Part 2: Letters 43 (7 B) L984-L986 2004年7月15日

    DOI: 10.1143/JJAP.43.L984  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    Magnetic tunnel junctions with a stacking structure of Cr/Co-Mn-Al/Al-O/Co- Fe/Ir-Mn were fabricated using a UHV magnetron-sputtering machine. Co-Mn-Al films showed B2 structure, which involves partial disorder between Mn and Al sites. Tunnel magnetoresistance ratios at room temperature were 27% and 40% before and after annealing at 250°C, respectively. Those values are much higher than the ones obtained in previous experiments using half Heusler alloys.

  278. Tunnel spectra for Al/Al-oxide/Ni80Fe20 junctions under the superconducting transition temperature of Al films 査読有り

    M. Oogane, T. Daibou, H. Kubota, Y. Ando, T. Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E1515-E1516 2004年5月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2003.12.318  

    ISSN:0304-8853

    詳細を見る 詳細を閉じる

    Superconductor/insulator/metal (S/I/M) tunnel junction can be used as an indicator of junction quality. For S/I/M junction, zero-bias conductance (ZBC) should be close to zero. However, leakage conductance increases the ZBC values. We measured the ZBC values of the Al/Al-oxide/ Ni80Fe20 junctions prepared with various oxidation processes. For strong plasma oxidation ( high applied power), most of the junctions showed low ZBC. However, ZBC increased with decreasing power of oxidation. It is considered that oxidation proceeds homogeneously for strong oxidation, compared with weak oxidation process. (C) 2003 Elsevier B.V. All rights reserved.

  279. Co<SUB>2</SUB>MnAlホイスラー合金を用いた強磁性トンネル接合 査読有り

    中田淳, 大兼幹彦, 久保田均, 安藤康夫, 加藤宏朗, 宮崎照宣

    日本応用磁気学会誌 28 (4) 573-576 2004年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.28.573  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    We investigated the structural and magnetic properties of Co<sub>2</sub>MnAl thin films with Cr buffer layers, and the tunnel magnetoresistance (TMR) effect of junctions using Co<sub>2</sub>MnAl Heusler alloy. The saturation magnetization of Co<sub>2</sub>MnAl film deposited at 350°C was 711 emu/cm<sup>3</sup> which was almost the same as that reported for bulk. The maximum TMR ratio of the junctions was 12% at room temperature and 26% at 25K. TMR ratio increased to 17% at room temperature after annealing at 200°C for one hour.

  280. Magnetic tunnel junctions with high magnetoresistance and small bias voltage dependence using epitaxial NiFe(111) ferromagnetic bottom electrodes 査読有り

    JH Yu, HM Lee, M Hayashi, M Oogane, T Daibou, H Nakamura, H Kubota, Y Ando, T Miyazaki

    JOURNAL OF APPLIED PHYSICS 93 (10) 8555-8557 2003年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1544458  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Magnetic tunnel junctions (MTJs) were fabricated using an Al-O insulating layer prepared on an epitaxially grown Ni80Fe20 bottom electrode and on a polycrystalline Ni80Fe20 bottom electrode. Crystallographic orientations and surface morphology of the films were examined using x-ray diffraction and atomic force microscopy, respectively. The MTJ with an epitaxial bottom electrode showed a tunnel magnetoresistance (TMR) ratio of 51% after annealing at 250 degreesC. This value was about two times larger than that of the MTJ with a polycrystalline bottom electrode (27%). The applied bias voltage dependences of the TMR ratios were also much different. The V-half values of epitaxial and polycrystalline samples were about 750 and 400 mV, respectively. (C) 2003 American Institute of Physics.

  281. Interface characterization of magnetic tunnel junctions by using tunneling spectroscopy 査読有り

    Y Ando, M Hayashi, M Oogane, H Kubota, T Miyazaki

    JOURNAL OF APPLIED PHYSICS 93 (10) 7023-7025 2003年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1540172  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Junctions doped with a small mount of Al between the top ferromagnetic electrode and the insulator were fabricated. The tunnel magnetoresistance (TMR) ratio increased at the doped Al thickness of 0.2 nm after annealing at 250degreesC. Inelastic-electron-tunneling spectroscopy (IETS) has been applied to investigate the spin-dependent tunneling process for the tunnel junctions. The IET spectrum subtracting the spectrum at parallel magnetization configuration from that at antiparallel configuration showed a peak around 20 mV of the bias voltage especially for the junction after annealing at 250degreesC. Over the corresponding voltage the TMR ratio as a function of the bias decreased; however, the influence was relatively small. (C) 2003 American Institute of Physics.

  282. Microfabrication and Magnetoelectric Properties of High-magnetoresistance Tunnel Junctions 査読有り

    X. F. Han, M. Oogane, T. Daibou, K. Yaoita, Y. Ando, H. Kubota, T. Miyazaki

    J. Magn. Soc. Jpn. 25 (4) 707-710 2001年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.25.707  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Spin-valve-type tunnel junctions with structure of Ta(5nm)/Ni<sub>79</sub>Fe<sub>21</sub>(3 nm)/Cu(20 nm)/Ni<sub>79</sub>Fe<sub>21</sub>(3 nm)/Ir<sub>22</sub>Mn<sub>78</sub> (10 nm)/Co<sub>75</sub>Fe<sub>25</sub>(4 nm)/Al(0.80 nm)-oxide /Co<sub>75</sub>Fe<sub>25</sub>(4 nm)/Ni<sub>79</sub>Fe<sub>21</sub>(20 nm)/Ta(5 nm) were fabricated using a microfabrication technique. The optical lithography combined with Ar ion-beam etching and CF<sub>4</sub> active etching was used to pattern the junction area with the size from 100x100 down to 3x3 μm<sup>2</sup>. A thinner barrier layer and a short plasma-oxidation time for Al-oxide layer were used in order to reduce the junction resistance and increase the TMR ratio. High TMR ratio of 69.1% at 4.2 K and 49.7% at room temperature were achieved. A spin-electron polarization tunneling model, based on magnon emission or absorption by the tunneling electrons during the tunnel process, was extended by defining an anisotropic wavelength cutoff energy of spin-wave in this work. Intrinsic magnetoelectric properties, such as the temperature dependence of TMR ratio and resistances from 4.2 to 300 K at 1.0 mV bias can be self-consistently evaluated using this extended model and a unique set of intrinsic parameters.

  283. 中間層にAl を用いた二重トンネル接合の磁気抵抗効果 査読有り

    大坊忠臣, 大兼幹彦, 安藤康夫, Changkyung Kim, Ohsung Song, 宮崎照宣

    日本応用磁気学会誌 25 (4) 767-770 2001年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.25.767  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Tunnel magnetoresistance for double barrier tunnel junctions with an intermediate layer of metallic Al was investigated. The junction with a 40-Å intermediate layer of Al showed a about 8.5%. TMR ratio. The TMR ratio decreased with increasing Al thickness and became zero at 100 Å. At a low temperature, Al thin film was expected to be in transition to superconductor. A superconducting gap was observed in the two junctions with 40-Å and 100-Å Al at about 0.4 K.

  284. 二重強磁性トンネル接合におけるスピン依存伝導特性 査読有り

    T. Siripongsakul, 大兼幹彦, 村井純一郎, Andrew C. C. Yu, 久保田均, 安藤康夫, 宮崎照宣, Changkyung Kim, Ohsung Song

    日本応用磁気学会誌 25 (4) 763-766 2001年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.25.763  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Ferromagnetic double barrier junctions of Co<sub>75</sub>Fe<sub>25</sub>/ Al<sub>2</sub>O<sub>3</sub>/ Co<sub>75</sub>Fe<sub>25</sub>(<i>X</i>)/ Al<sub>2</sub>O<sub>3</sub>/ Co<sub>75</sub>Fe<sub>25</sub> with discontinuous middle Co<sub>75</sub>Fe<sub>25</sub> layers (<i>X</i> = 0, 0.7, 1.3, 2.0 nm) were fabricated, and magnetoresistance of these junctions was measured by a dc-4-probe method. At low temperature, the resistance and TMR ratio increased rapidly. This result implies the existence of a charging effect due to the Coulomb-blockade. At temperatures below 50 K, an ac-modulation method was used to measure bias-voltage dependence of the TMR ratio. We observed an increase in TMR ratio for the case of dc transport at low bias voltage. On the other hand, the TMR ratio decreased for the case of ac transport. At high bias voltage and at high temperature, however, we observed no difference between these methods. Such transport properties could be explained by a co-tunneling process.

  285. Analyses of intrinsic magnetoelectric properties in spin-valve-type tunnel junctions with high magnetoresistance and low resistance 査読有り

    Xiu-Feng Han, Andrew C.C. Yu, Mikihiko Oogane, Junichirou Murai, Tadaomi Daibou, Terunobu Miyazaki

    Physical Review B - Condensed Matter and Materials Physics 63 (22) 2001年

    DOI: 10.1103/PhysRevB.63.224404  

    ISSN:1550-235X 1098-0121

    詳細を見る 詳細を閉じる

    A series of experimental data was obtained systematically for a spin-valve-type tunnel junction of (formula presented) (3 nm)/Cu (formula presented) (formula presented) (4 nm)/Al (formula presented) (formula presented) (20 nm)/Ta (5 nm). Analyses of (i) temperature dependence of tunnel magnetoresistance (TMR) ratio and resistance from 4.2 K to room temperature, (ii) applied dc bias-voltage dependence of TMR ratio and resistance at 6.0 K and room temperature, and (iii) tunnel current I and dynamic conductance (formula presented) as functions of dc bias voltage at 6.0 K were carried out. High-TMR ratio of 64.7% at 4.2 K and 44.2% at room temperature were observed for this junction after annealing at 300 °C for an hour. An anisotropic wavelength cutoff energy of spin-wave spectrum in magnetic tunnel junctions, which is essential for self-consistent calculations, was suggested based on a series of inelastic electron tunnel spectra obtained. The main intrinsic magnetoelectric properties in such spin-valve-type tunnel junction with high magnetoresistance and low resistance can be evaluated based on the magnon-assisted inelastic excitation model and theory. © 2001 The American Physical Society.

  286. Fabrication of high-magnetoresistance tunnel junctions using Co75Fe25 ferromagnetic electrodes 査読有り

    XF Han, M Oogane, H Kubota, Y Ando, T Miyazaki

    APPLIED PHYSICS LETTERS 77 (2) 283-285 2000年7月

    出版者・発行元:AMER INST PHYSICS

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature and applied voltage dependence of the TMR ratio and resistance at room temperature for a tunnel junction, Ta (5 nm)/Ni79Fe21 (3 nm)/Cu (20 nm)/Ni79Fe21 (3 nm)/Ir22Mn78 (10 nm)/Co75Fe25 (4 nm)/Al (0.8 nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 (20 nm)/Ta(5 nm), were investigated. TMR ratio, effective barrier height and width, and breakdown voltage of the junction can be remarkably enhanced after annealing at 300 degrees C for an hour. High TMR ratio of 49.7% at room temperature and 69.1% at 4.2 K were observed. The value of spin polarization of Co75Fe25, P = 50.7%, deduced from the TMR ratio at 4.2 K was corresponding well to the experimental data measured at 0.2 K in a spin polarized tunneling experiment using a superconductor/insulator/ferromagnet tunneling junction. (C) 2000 American Institute of Physics. [S0003-6951(00)05028-2].

  287. Applied voltage and temperature dependence of tunneling magnetoresistance 査読有り

    N. Tezuka, M. Oogane, T. Miyazaki

    Journal of Magnetism and Magnetic Materials 1999年3月

    DOI: 10.1016/S0304-8853(98)01056-7  

  288. 強磁性体/Al-Oxide/Co接合のトンネル磁気抵抗効果の印加電圧及び温度依存性 査読有り

    大兼幹彦, 手束展規, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1297-1300 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1297  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Ferromagnetic tunneling junctions with various thicknesses of the first ferromagnetic layer were fabricated. Co and Ni<sub>80</sub>Fe<sub>20</sub> were used as the first ferromagnetic layer, and their thicknesses were varied between 10 and 200 Å. The voltage and temperature dependence of the tunneling magnetoresistance (TMR) ratio and conductance characteristic were investigated for these junctions. A drastic decrease in the conductance near the zero bias in the conductance-voltage characteristics (zero-bias anomaly) was observed in some junctions. A rapid decrease in the TMR ratio below 5 mV and 50 K was also observed in the same junctions. A slight decrease in the TMR ratio above 10 mV and 100 K was observed in all junctions. We investigated the origin of the voltage and temperature dependence of the TMR ratio by taking account of the magnetic impurity and magnon effect.

  289. Ni80Fe20/Al-Oxide/Co接合におけるトンネル磁気抵抗比のNi80Fe20膜厚依存性 査読有り

    大兼幹彦, 手束展規, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1309-1312 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1309  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Ferromagnetic tunneling junctions with various thicknesses of the first ferromagnetic layer were fabricated. Ni<sub>80</sub>Fe<sub>20</sub> and Co were used as the first ferro-magnetic layer, and their thicknesses were varied between 10 and 200 Å. The tunneling magnetoresistance (TMR) ratio decreased and the shape of the TMR curve changed with decreasing Ni<sub>80</sub>Fe<sub>20</sub> thickness, but changed only slightly with decreasing Co thickness. We calculated the TMR and magnetization curves by using a simple model that takes account of magnetic anisotropy to explain the change in the TMR ratio and the shape of the TMR curve with changing Ni<sub>80</sub>Fe<sub>20</sub> thickness.

︎全件表示 ︎最初の5件までを表示

MISC 56

  1. TMRセンサによる生体磁場計測の進展

    大兼幹彦, 大兼幹彦, 藤原耕輔, 菅野彰剛, 中野貴文, 我妻宏, 有本直, 水上成美, 水上成美, 熊谷静似, 松崎斉, 松崎斉, 中里信和, 安藤康夫, 安藤康夫

    応用物理学会春季学術講演会講演予稿集(CD-ROM) 70th 2023年

    ISSN:2436-7613

  2. トンネル磁気抵抗センサによるサブピコテスラ磁界検出

    大兼幹彦, 大兼幹彦, 藤原耕輔, 菅野彰剛, 中野貴文, 我妻宏, 有本直, 水上成美, 水上成美, 熊谷静似, 松崎斉, 松崎斉, 中里信和, 安藤康夫, 安藤康夫

    応用物理学会春季学術講演会講演予稿集(CD-ROM) 70th 2023年

    ISSN:2436-7613

  3. 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野彰剛, 大兼幹彦, 藤原耕輔, 柿坂庸介, 松崎斉, 安藤康夫, 中里信和

    臨床神経生理学(Web) 49 (5) 2021年

    ISSN:2188-031X

  4. TMRセンサの原理と心磁図計測

    大兼幹彦, 大兼幹彦, 大兼幹彦, 菅野彰剛, 藤原耕輔, 中野貴文, 熊谷静似, 松崎斉, 中里信和, 安藤康夫

    臨床神経生理学(Web) 49 (5) 2021年

    ISSN:2188-031X

  5. 頭皮上に密着可能なトンネル磁気抵抗素子を用いた室温脳磁計の開発

    菅野彰剛, 大兼幹彦, 藤原耕輔, 柿坂庸介, 松崎斉, 安藤康夫, 中里信和

    臨床神経生理学(Web) 49 (5) 2021年

    ISSN:2188-031X

  6. TMRセンサを用いたリアルタイム心磁図計測

    大兼幹彦, 菅野彰剛, 藤原耕輔, 松崎斉, 中里信和, 安藤康夫

    日本生体医工学会大会プログラム・抄録集(Web) 60th 2021年

  7. トンネル磁気抵抗素子を用いた室温脳磁計による体性感覚誘発磁界の測定

    菅野彰剛, 大兼幹彦, 藤原耕輔, 松崎斉, 安藤康夫, 中里信和

    日本生体磁気学会誌 34 (1) 2021年

    ISSN:0915-0374

  8. 研究室紹介 招待有り

    大兼 幹彦

    真空ジャーナル 9 2018年9月

  9. TMR磁気センサ 招待有り

    大兼 幹彦

    まぐね 12 (5) 2017年12月

  10. Anisotropic magnetic property of nanocomposite Nd<inf>2</inf>Fe<inf>14</inf>B/Mo/α-Fe multilayer films

    K. Kobayashi, D. Ogawa, K. Koike, H. Kato, M. Oogane, T. Miyazaki, Y. Ando, M. Itakura

    Journal of Physics: Conference Series 903 2017年10月28日

    DOI: 10.1088/1742-6596/903/1/012015  

    ISSN:1742-6588

    詳細を見る 詳細を閉じる

    © 2016 Published under licence by IOP Publishing Ltd. We fabricated the MgO(100)/Mo/[Nd2Fe14B/Mo/Fe/Mo]5/Mo multilayer films, in which we tried to avoid the negative Jexinterfaces and thermal diffusion between Nd2Fe14B and α-Fe layers by forming the stacked structure with ultra thin Mo interlayer. The films without Mo interlayer showed isotropic magnetic properties, while films with Mo interlayer thickness tMo= 1 nm exhibited the perpendicular anisotropy with the coercivity of 7 kOe. Shapes for the major loop and the first order reversal curves (FORCs) suggested an existence of positive exchange coupling between the Nd-Fe-B and the α-Fe layers via the 1 nm thick Mo interlayer.

  11. 生体磁場測定応用の為の高感度TMRセンサの開発 (高周波用磁気デバイス・材料・評価技術の現状と新展開)

    城野 純一, 藤原 耕輔, 大兼 幹彦, 寺内 孝, 土田 匡章, 安藤 康夫

    社団法人日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan 212 33-38 2017年2月21日

    出版者・発行元:日本磁気学会

    ISSN:1882-2940

  12. Systematic investigation on correlation between sensitivity and nonlinearity in magnetic tunnel junction for magnetic sensor.

    T. Nakano, M. Oogane, H. Naganuma, Y. Ando

    2015 IEEE MAGNETICS CONFERENCE (INTERMAG) 2015年

    出版者・発行元:IEEE

  13. 界面装飾した強磁性トンネル接合の作製と磁気抵抗効果

    安藤 康夫, 大兼 幹彦, 永沼 博

    東北大学極低温科学センターだより (15) 3-6 2014年11月

    出版者・発行元:東北大学極低温科学センター

  14. 低磁気緩和を有するハーフメタルホイスラー合金

    大兼 幹彦, 水上 成美, 窪田 崇秀, 小田 洋平, 佐久間 昭正, 永沼 博, 安藤 康夫

    日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan 183 21-24 2012年3月22日

    出版者・発行元:日本磁気学会

    ISSN:1882-2940

  15. MgO障壁を用いたFePt垂直磁化トンネル磁気抵抗素子の磁気抵抗特性および極微構造

    井波暢人, 永沼博, 金国天, 宮崎孝道, 佐藤和久, 今野豊彦, 大兼幹彦, 安藤康夫

    日本磁気学会誌 34 (3) 293-296 2010年3月

    出版者・発行元:日本磁気学会

    DOI: 10.3379/msjmag.1003R047  

    ISSN:1882-2924

    詳細を見る 詳細を閉じる

    Perpendicularly magnetized magnetic tunnel junctions (MTJs) were fabricated by depositing thin L1<sub>0</sub>-ordered FePt films on MgO(001) substrates using a UHV sputtering system, and the dependence of structural, magnetic, and magnetotransport properties of the junctions on the thickness of the FePt layers was investigated. A full epitaxial structure of MgO(001) sub./Cr/Pt/FePt/MgO/CoPt/Ta was observed. The tunnel magnetoresistance (TMR) ratio was measured to be 6% at room temperature, and magnetization switching was clearly observed in the thin FePt layer. Transmission electron microscopy (TEM) observations revealed that the interface between FePt, MgO, and CoPt layer has strain due to lattice mismatch, which might be a reason for the low TMR ratio.

  16. Optically induced magnetization dynamics and variation of damping parameter in epitaxial Co2MnSi Heusler alloy films

    Y. Liu, L. R. Shelford, V. V. Kruglyak, Y. Sakuraba, M. Oogane, R. J. Hicken, Y. Ando

    Physical Review B 81 (9) 094402 2010年

    DOI: 10.1103/PhysRevB.81.094402  

    ISSN:1098-0121

  17. Evidence of Fermi level control in a half-metallic Heusler compound Co2MnSi by Al-doping: Comparison of measurements with first-principles calculations

    Y. Sakuraba, Y. Kota, T. Kubota, M. Oogane, A. Sakuma, Y. Ando, K. Takanashi

    Physical Review B 81 (14) 144422 2010年

    DOI: 10.1103/PhysRevB.81.144422  

    ISSN:1098-0121

  18. 26aVD-7 垂直磁化Pt/Co/Pt三層膜における時間分解磁気光学効果(スピン流・スピンホール,領域3,磁性,磁気共鳴)

    水上 成美, Sajitha E. P., 渡邉 大輔, Wu F., 大兼 幹彦, 永沼 博, 安藤 康夫, 宮崎 照宣

    日本物理学会講演概要集 64 (2) 360-360 2009年8月18日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  19. Fe-Co-NiおよびCo基フルホイスラー合金薄膜における磁気緩和

    水上成美, 大兼幹彦, 窪田嵩秀, 渡邉大輔, 永沼博, 安藤康夫, 宮崎照宣

    日本磁気学会誌 まぐね 4 (5) 229-235 2009年4月

  20. スピントルク磁化反転におけるスピンダイナミクス

    安藤 康夫, 青木 達也, 玉川 聖, 渡邉 大輔, 水上 成美, 家形 諭, 谷口 知大, 今村 裕志, 永沼 博, 大兼 幹彦, 井波 暢人, 宮崎 照宣

    日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan 165 25-30 2009年3月13日

    出版者・発行元:日本磁気学会

    ISSN:1882-2940

  21. 27aTF-12 磁性金属薄膜のスピン緩和の光学的検出(27aTF スピンホール・磁気渦・ダイナミクス,領域3(磁性,磁気共鳴))

    水上 成美, 大兼 幹彦, 安藤 康夫, 宮崎 照宣

    日本物理学会講演概要集 64 (1) 431-431 2009年3月3日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  22. スピンポンピングによるスピン流の創出と物理現象 招待有り 査読有り

    安藤康夫, 水上成美, 家形論, 谷口知大, 今村裕志, 大兼幹彦, 宮崎照宣

    まぐね 4 (2) 73-81 2009年2月

    出版者・発行元:日本磁気学会

    ISSN:1880-7208

  23. ホイスラー合金Co2MnSiを用いた高感度磁気抵抗素子の開発

    桜庭裕弥, 岩瀬拓, 常木澄人, 斉藤今朝美, 大兼幹彦, 安藤康夫, 佐久間昭正, 高梨弘毅

    IEICE Technical Report (MR2008) 32 2008年11月

    詳細を見る 詳細を閉じる

    Development of high-sensitive magnetoresistance devices using half-metallic Heusler alloy Co2MnSi

  24. Development of high-sensitive magnetoresistance devices using half-metallic Heusler alloy Co2MnSi

    Y. Sakuraba, T. Iwase, S. Tsunegi, K. Saito, M. Oogane, Y. Ando, A. Sakuma, K. Takanashi

    IEICE Technical Report MR 32 2008年

  25. 強磁性共鳴を用いたMRAMフリー層材料の磁気緩和定数測定

    安藤 康夫, 大兼 幹彦, 渡邉 大輔, 渡邉 美穂, YILGIN R., 家形 諭, 宮崎 照宣

    日本応用磁気学会研究会資料 153 7-14 2007年2月27日

    ISSN:1340-7562

  26. IETS法によるMgO-TMR膜のバリア構造観測

    玉野井健, 大兼幹彦, 安藤康夫, 田中努, 上原裕二, 渦巻拓也

    次世代磁気記録材料・システムへの挑戦 2007年

  27. MgOバリアTMR膜の電気伝導特性

    玉野井健, 大兼幹彦, 安藤康夫, 田中努, 上原裕二, 渦巻拓也

    日本応用磁気学会学術講演概要集 31st 2007年

    ISSN:1340-8100

  28. Magnetic damping constant of Co2FeSi Heusler alloy thin film

    M. Oogane, R. Yilgin, Ma. Shinano, S. Yakata, Y. Sakuraba, Y. Ando, T. Miyazaki

    Journal of Applied Physic 2007年

    DOI: 10.1063/1.2709751  

  29. New Magnetic Nano-Dot Memory with FePt Nano-Dots

    YIN Cheng-Kuan, BEA Ji-Chel, MURUGESAN Mariappan, OOGANE Mikihiko, FUKUSHIMA Takafumi, TANAKA Tetsu, NATORI Kenji, MIYAO Masanobu, KOYANAGI Mitsumasa

    Extended abstracts of the ... Conference on Solid State Devices and Materials 2006 994-995 2006年9月13日

  30. Interfacial structure and half-metallic ferromagnetism in Co2MnSi-based magnetic tunnel junctions

    N. D. Telling, P. Keatley, G. van, der Laan, R. J. Hicken, E. Arenholz, Y. Sakuraba, M. Oogane, Y. Ando, T. Miyazaki

    Physical Review B 74 (22) 224439 2006年

    DOI: 10.1103/PhysRevB.74.224439  

    ISSN:1098-0121

  31. Co2MnSi(110)エピタキシャル薄膜を用いた強磁性トンネル接合の作製

    服部 正志, 桜庭 裕弥, 大兼 幹彦, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会誌 31 (2) 89-93 2006年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.31.89  

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    According to Julliere's model, magnetic tunnel junctions (MTJs) with half-metallic electrodes lead to a large tunnel magnetoresistance (TMR) ratio. A Co<sub>2</sub>MnSi Heusler alloy is theoretically expected to exhibit half-metallicity. We fabricated (110)-oriented epitaxial Co<sub>2</sub>MnSi electrodes on sapphire substrates using W and Ta/W/Cr buffer layers. With the W buffer layer, we found that the W and Co<sub>2</sub>MnSi layers formed a twin structure. However, with the Ta/W/Cr multi-buffer layers, we succeeded in fabricating a high-quality Co<sub>2</sub>MnSi(110) epitaxial electrode. We fabricated a MTJ with the high-quality Co<sub>2</sub>MnSi(110) electrode and investigated TMR effects in the MTJ. As a result, we observed a TMR ratio of about 40% at room temperature and 120% at 2 K.

  32. 24aXN-3 強磁性体二重トンネル接合を利用した超伝導体中へのスピン注入とその磁気抵抗効果(薄膜・人工格子磁性,表面・界面磁性,トンネル分光,領域3(磁性,磁気共鳴))

    大坊 忠臣, 大兼 幹彦, 安藤 康夫, 宮崎 照宜

    日本物理学会講演概要集 60 (1) 407-407 2005年3月4日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  33. 24aXN-1 Fe/MgO/Fe強磁性トンネル接合の非弾性電子トンネル分光(薄膜・人工格子磁性,表面・界面磁性,トンネル分光,領域3(磁性,磁気共鳴))

    宮越 健史, 安藤 康夫, 大兼 幹彦, 宮崎 照宜, 久保田 均, 福島 章雄, 長浜 太郎, 湯浅 新治

    日本物理学会講演概要集 60 (1-3) 407-407 2005年3月4日

    出版者・発行元:社団法人日本物理学会

    ISSN:1342-8349

  34. Co_2MnAlを用いた強磁性トンネル接合の磁気抵抗効果

    中田 淳, 大兼 幹彦, 久保田 均, 安藤 康夫, 加藤 宏朗, 佐久間 昭正, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 28 395-395 2004年9月21日

  35. スパッタリング法によるCo_2MnAlエピタキシャル薄膜の作製

    桜庭 裕弥, 中田 淳, 大兼 幹彦, 久保田 均, 安藤 康夫, 加藤 宏朗, 佐久間 昭正, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 28 394-394 2004年9月21日

  36. 強磁性体二重トンネル接合による超伝導体へのスピン注入

    大坊 忠臣, 大兼 幹彦, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 28 123-123 2004年9月21日

  37. ホイスラー系合金Co_2MnAlを用いた強磁性トンネル接合

    中田 淳, 大兼 幹彦, 久保田 均, 安藤 康夫, 加藤 宏朗, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 27 266-266 2003年9月1日

    ISSN:1340-8100

  38. トンネルスピン分極率の強磁性層作製条件依存性

    大兼 幹彦, 大坊 忠臣, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 27 434-434 2003年9月1日

    ISSN:1340-8100

  39. 強磁性体//超伝導体//強磁性体二重接合の磁気抵抗効果

    大坊 忠臣, 大兼 幹彦, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 27 435-435 2003年9月1日

    ISSN:1340-8100

  40. Magnetic tunnel junction using an epitaxial Ni_<80>Fe_<20> thin film grown on a a single crystal Si substrate

    YU J. H., LEE H. M., HAYASHI M., OOGANE M., KUBOTA H., ANDO Y., MIYAZAKI T.

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 26 10-10 2002年9月1日

    ISSN:1340-8100

  41. Al/Al-oxide/ 強磁性体接合のトンネルコンダクタンス特性

    大兼 幹彦, 大坊 忠臣, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 26 9-9 2002年9月1日

    ISSN:1340-8100

  42. Magnetoresistance in Ce3Fe29-xTx (T = V and Cr)

    XF Han, ZG Sun, H Kato, M Oogane, BG Shen, FM Yang, JMD Coey

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 239 (1-3) 204-206 2002年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(01)00558-3  

    ISSN:0304-8853

    詳細を見る 詳細を閉じる

    A magnetoresistance ratio of about 38% was observed with an external magnetic field applied perpendicular and parallel to the DC current direction at 4.2K for the bulk samples of Ce3Fe29-xVx, and Ce3Fe29-xCrx respectively. It is suggested that the magnetoresistance mainly originated from the magnetic moment and domain-wall scattering to the conduction electrons in these compounds. (C) 2002 Elsevier Science B.V, All rights reserved.

  43. Fabrication of magnetic tunnel junctions using epitaxial NiFe (111) ferromagnetic bottom electrodes

    H. Yu, M. Hayashi, M. Oogane, H. Kubota, Y. Ando, T. Miyazaki, H. M. Lee

    Appl. Phys. Lett 2002年

  44. トンネル分光法を用いたスピン分極率測定

    大兼 幹彦, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 25 336-336 2001年9月1日

    ISSN:1340-8100

  45. 中間層を超伝導体とする二重トンネル接合の磁気抵抗効果

    大坊 忠臣, 大兼 幹彦, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 25 344-344 2001年9月1日

    ISSN:1340-8100

  46. 強磁性トンネル接合における絶縁層の酸化過程

    林 将光, 安藤 康夫, 大兼 幹彦, 久保田 均, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 25 339-339 2001年9月1日

    ISSN:1340-8100

  47. 28aYE-5 中間層を超伝導体とする二重トンネル接合の磁気抵抗効果

    大坊 忠臣, 大兼 幹彦, 安藤 康夫, Kim C., Song O., 宮崎 照宣

    日本物理学会講演概要集 56 (1) 711-711 2001年3月9日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  48. 中間層にAlを用いた二重トンネル接合の磁気抵抗効果

    大坊 忠臣, 大兼 幹彦, 安藤 康夫, KIM Changkyung, SONG Ohsung, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 24 52-52 2000年9月1日

    ISSN:1340-8100

  49. Transport properties in ferromagnetic double barrier junctions

    SIRIPONGSAKUL T., OOGANE M., MURAI J., YU Andrew C. C., KUBOTA H., ANDO Y., MIYAZAKI T., KIM Changkyung, SONG Ohsung

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 24 51-51 2000年9月1日

    ISSN:1340-8100

  50. 24pPSB-30 トンネル分光法によるFe,Co,Niのスピン分極率測定

    大兼 幹彦, 手束 展規, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本物理学会講演概要集 55 (1) 410-410 2000年3月10日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  51. Large anisotropic magnetoresistance in Ce_3Fe_<29-x>T_x(T=V and Cr)

    HAN X. F., OOGANE M., MIYAZAKI T.

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 23 61-61 1999年10月1日

  52. 26pPSA-45 トンネル分光法によるスピン分極率測定

    大兼 幹彦, 手束 展規, 久保田 均, 安藤 康夫, 宮崎 照宣

    日本物理学会講演概要集 54 (2) 419-419 1999年9月3日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  53. Ni_<80>Fe_<20>/Al-Oxide/Co接合におけるトンネル磁気抵抗比のNi_<80>Fe_<20>膜厚依存性

    大兼 幹彦, 手束 展規, 宮崎 照宣

    日本応用磁気学会誌 23 (4) 1309-1312 1999年4月15日

    出版者・発行元:日本応用磁気学会

    ISSN:0285-0192

    詳細を見る 詳細を閉じる

    Ferromagnetic tunneling junctions with various thicknesses of the first ferromagnetic layer were fabricated. Ni_<80>Fe_<20> and Co were used as the first ferromagnetic layer, and their thickness were varied between 10 and 200Å. The tunneling magnetoresistance (TMR) ratio decreased and the shape of the TMR curve changed with decreasing Ni_<80>Fe_<20> thickness, but changed only slightly with decreasing Co thickness. We calculated the TMR and magnetization curves by using a simple model that takes account of magnetic anisotropy to explain the change in the TMR ratio and the shape of the TMR curve with changing Ni_<80>Fe_<20> thickness.

  54. 28p-J-12 Co/Al-oxide/Co接合におけるTMR比の印加電圧・温度依存性

    大兼 幹彦, 手束 展規, 宮崎 照宣

    日本物理学会講演概要集 54 (1) 412-412 1999年3月15日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  55. 80NiFe/Al-oxide/Co接合におけるトンネル磁気抵抗比の80NiFe膜厚依存性

    大兼 幹彦, 手束 展規, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 22 460-460 1998年9月1日

  56. 強磁性体/Al-oxide/Co接合のトンネル磁気抵抗効果の印加電圧及び温度依存性

    大兼 幹彦, 手束 展規, 宮崎 照宣

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 22 457-457 1998年9月1日

︎全件表示 ︎最初の5件までを表示

書籍等出版物 6

  1. スピントロニクスハンドブック : 基礎から応用まで

    スピントロニクスハンドブック編集委員会, 佐橋, 政司, 湯浅, 新治, 遠藤, 哲郎

    エヌ・ティー・エス 2023年5月

    ISBN: 9784860438425

  2. Nanomagnetic materials : fabrication, characterization and application

    Mikihiko Oogane

    2021年

    ISBN: 9780128223499

  3. 磁性材料・部品の 最新開発事例と応用技術

    大兼 幹彦

    技術情報協会 2018年3月

  4. 新しい磁気センサとその応用

    毛利佳年雄, 安藤康夫, 本蔵義信, 大兼幹彦, 内山剛, 野々村裕

    2013年

  5. スピントロニクスの基礎と材料・応用技術の最前線

    大兼幹彦, 宮崎照宣

    2009年

  6. Epitaxial ferromagnetic metal films and spintronic applications

    M. Oogane, T. Miyazaki

    2008年

︎全件表示 ︎最初の5件までを表示

講演・口頭発表等 44

  1. Magnetic tunnel junctions designed for highly-sensitive magnetic sensor applications 招待有り

    2023年8月22日

  2. Development of TMR sensor for bio-magnetic field detection 招待有り

    2023年5月25日

  3. Magnetic tunnel junction using soft magnetic CoFeSiB-based composite free layer for magnetic sensor applications 招待有り

    2023年5月14日

  4. TMRセンサの開発とミニマルファブへの期待 招待有り

    大兼 幹彦

    ファブシステム研究会 令和5年度リアル春季大会 2023年4月21日

  5. Spintronic sensor and its applications 招待有り

    Korea University MSE seminar 2023年4月11日

  6. スピントロニクスセンサの開発と展望 招待有り

    大兼幹彦

    電気学会ナノ磁性研究会 2023年3月31日

  7. TMRセンサによる生体磁場計測の進展 招待有り

    大兼 幹彦, 藤原 耕輔, 菅野 彰剛, 中野 貴文, 我妻 宏, 有本 直, 水上 成美, 熊谷 静似, 松﨑 斉, 中里 信和, 安藤 康夫

    第70回応用物理学会春季学術講演会 2023年3月18日

  8. トンネル磁気抵抗センサによるサブピコテスラ磁界検出 招待有り

    大兼 幹彦, 藤原 耕輔, 菅野 彰剛, 中野 貴文, 我妻 宏, 有本 直, 水上 成美, 熊谷 静似, 松﨑 斉, 中里 信和, 安藤 康夫

    第70回応用物理学会春季学術講演会 2023年3月17日

  9. TMR磁気センサの基礎と応用 招待有り

    大兼幹彦

    2023年電子情報通信学会 2023年3月9日

  10. TMR磁気センサの高感度化技術と応用展開 招待有り

    大兼 幹彦

    第30回 磁気応用技術シンポジウム 2022年8月23日

  11. スピントロニクスセンサの生体磁場計測応用 招待有り

    大兼 幹彦

    第37回日本生体磁気学会 2022年6月15日

  12. TMRセンサの高感度化の現状と今後の応用展開 招待有り

    大兼 幹彦

    センシング技術応用セミナー 2022年6月14日

  13. Measurement of Bio-magnetic Fields with Tunnel Magneto-resistive Sensors 招待有り

    2021年12月29日

  14. TMRセンサの原理と心磁図計測 招待有り

    大兼幹彦, 菅野彰剛, 藤原耕輔, 熊谷静似, 松﨑斉, 中里信和, 安藤康夫

    第51回日本臨床神経生理学会学術大会 2021年12月16日

  15. Development of highly sensitive bio-magnetic TMR sensors 招待有り

    Mikihiko Oogane

    2021年10月29日

  16. Development of highly sensitive TMR based sensor 招待有り

    M. Oogane, K. Fujiwara, S. Kumagai, H. Matsuzaki, Y. Ando

    2021年9月2日

  17. Tunnel magneto-resistance effect in magnetic tunnel junctions 国際会議 招待有り

    大兼 幹彦

    SSDM2018 2018年7月12日

  18. TMRセンサ材料および素子開発の進展 招待有り

    大兼 幹彦

    第68回スピンエレクトロニクス専門研究会 2018年7月6日

  19. Super-sensitive magnetic tunnel junction based sensor devices 国際会議 招待有り

    大兼 幹彦

    NIMS special seminar 2018年5月16日

  20. Mnを含む強磁性規則合金の スピントロニクス応用 招待有り

    大兼 幹彦

    第184回スピニクス研究会 2017年7月28日

  21. スピンエレクトロニクス材料・デバイスの基礎 招待有り

    大兼 幹彦

    第40回日本磁気学会 サマースクール 2017年6月9日

  22. 強磁性トンネル接合を用いた高感度磁場センサ開発

    第2回高周波スピントロニクス研究会 2016年2月22日

  23. スピントロニクスデバイス開発の最前線

    SLiT-J Workshop 2016年1月19日

  24. Tunnel magneto resistance effect in MTJs with Mn-based ordered alloys 国際会議

    The 13th RIEC International Workshop on Spintronics 2015年11月18日

  25. スピンエレクトロニクス材料・デバイスの基礎

    第38回日本磁気学会サマースクール 2015年7月24日

  26. Fabrication of highly ordered Co2Fe0.4Mn0.6Si Heusler alloys on Si substrate

    34rd Electronic Materials Symposium 2015年7月15日

  27. Highly ordered Co2Fe0.4Mn0.6Si Heusler alloy films for Spin-FET devices 国際会議

    The 1st【ImPACT】International Symposium on Spintronic Memory, Circuit and Storage 2015年6月21日

  28. Perpendicularly magnetized L10-ordered alloys for magnetic tunnel junctions 国際会議

    York-Tohoku-Kaiserslautern symposium 2015年6月11日

  29. Magnetic Tunnel Junctions with Amorphous CoFeSiB Free Layer for Highly Sensitive Magnetic Sensor Devices

    33rd Electronic Materials Symposium 2014年7月9日

  30. スピンエレクトロニクス材料・デバイスの基礎

    第37回日本磁気学会サマースクール 2014年7月8日

  31. Tunnel Magneto-resistance Effect in Magnetic Tunnel Junctions using Half-metallic Heusler Alloy Electrodes and a MgO Tunneling Barrier 国際会議

    2008 MRS Fall Meeting 2008年12月2日

  32. Tunnel magnetoresistance effect in magnetic tunnel junctions with Co-Mn-Si Heusler alloy electrode 国際会議

    53rd MMM conference 2008年11月12日

  33. フルホイスラー合金の磁気緩和定数測定

    第69回応用物理学会 学術講演会 2008年9月2日

  34. Magnetic damping constants in (CoFeB)Cr and (CoFeB)V alloy thin films 国際会議

    52nd MMM 2007年11月5日

  35. ホイスラー合金の磁性とそれを用いたトンネル接合における磁気抵抗効果

    第68回応用物理学会学術講演会 2007年9月6日

  36. Tunnel magneto resistance in MTJs with epitaxially grown Heusler alloy elecrodes 国際会議

    M. Oogane, M. Hattori, Y. Sakuraba, Y. Ando, T. Miyazaki

    ISAMMA2007 2007年5月

  37. Tunnel magnetoresistance effect in MTJs with Heusler alloy electrodes 国際会議

    Workshop on Spin Current 2007年2月19日

  38. Tunnel magnetoresistance in MTJs with Co2MnSi electrode and MgO barrier 国際会議

    M. Oogane, Y. Sakuraba, M. Hattori, Y. Ando, T. Miyazaki

    The 2nd RIEC International Workshop on Spintronics, Sendai 2007年2月15日

  39. M. Oogane, R. Yilgin, M. Watanabe, S. Yakata, Y. Sakuraba, Y. Ando and T. Miyazaki 国際会議

    M. Oogane, R. Yilgin, M. Watanabe, S. Yakata, Y. Sakuraba, Y. Ando, T. Miyazaki

    10th Joint MMM/Intermag 2007年1月

  40. Gilbert Damping Constant in Co-Fe-B Films 国際会議

    M. Oogane, M. Watanabe, S. Yakata, Y. Ando, T. Miyazaki

    ICMFS2006 2006年8月

  41. Tunnel Magnetoresistance Effect in Co2XSi(X=Cr,Mn,Fe)/Al-O/CoFe Junctions 国際会議

    M. Oogane, M. Shinano, R. Yilgin, Y. Sakuraba, H. Kubota, Y. Ando, A. Sakuma, T. Miyazaki

    ICM2006 2006年8月

  42. ホイスラー合金の磁性と磁気伝導特性

    大兼幹彦, 桜庭裕弥, R. Yilgin, 信濃正紹, 服部正志, 村上修一, 久保田均, 安藤康夫, 加藤宏朗, 佐久間昭正, 宮崎照宣

    第12回スピンエレクトロニクス専門研究会 2006年7月24日

  43. Gilbert damping constants in various ferromagnetic thin films 国際会議

    M. Oogane, T. Wakitani, S. Yakata, R. Yilgin, Y. Ando, A. Sakuma, T. Miyazaki

    The 1st RIEC International Workshop on Spintronics, Sendai 2006年2月8日

  44. Gilbert Damping Constants in Ni-Co, Ni-Fe and Half-metallic Heusler Alloy Thin Films 国際会議

    M. Oogane, T. Wakitani, S. Yakata, R. Yilgin, Y. Ando, A. Sakuma, T. Miyazaki

    50thMMM 2004年11月

︎全件表示 ︎最初の5件までを表示

産業財産権 18

  1. 磁気抵抗素子の製造方法

    藤原耕輔, 安藤康夫, 大兼幹彦

    特許第7128476号

    産業財産権の種類: 特許権

  2. 磁気センサ素子

    大兼幹彦, 安藤康夫

    特許第7106103号

    産業財産権の種類: 特許権

  3. Mn系強磁性薄膜およびその製造方法、ならびにMn系強磁性薄膜を有する磁気トンネル接合素子

    大兼 幹彦, 安藤 康夫, 栗本 雄太, 渡部 健太, 窪田 美穂

    特許第6985708号

    産業財産権の種類: 特許権

  4. トンネル磁気抵抗素子の製造方法

    安藤 康夫, 大兼 幹彦, 藤原 耕輔, 城野 純一

    特許第6978000号

    産業財産権の種類: 特許権

  5. トンネル磁気抵抗素子及び磁化方向補正回路

    安藤 康夫, 大兼 幹彦, 藤原 耕輔, 城野 純一, 寺内 孝, 関根 孝二郎, 土田 匡章

    特許第6969751号

    産業財産権の種類: 特許権

  6. トンネル磁気抵抗素子及びその製造方法

    安藤 康夫, 大兼 幹彦, 藤原 耕輔, 城野 純一, 土田 匡章

    特許第6923881号

    産業財産権の種類: 特許権

  7. Mn系強磁性薄膜の製造方法およびMn系強磁性薄膜

    大兼 幹彦, 安藤 康夫, 渡部 健太

    特許第6870850号

    産業財産権の種類: 特許権

  8. 磁気センサ

    小笠原 貴大, 大兼 幹彦, 角田 匡清, 安藤 康夫

    特許第6702034号

    産業財産権の種類: 特許権

  9. 磁気抵抗素子及び磁気抵抗素子の製造方法

    安藤 康夫, 大兼 幹彦, 藤原 耕輔, 城野 純一, 関根 孝二郎, 土田 匡章

    産業財産権の種類: 特許権

  10. FeSiAl合金薄膜およびFeSiAl合金薄膜の製造方法、ならびに、磁気センサおよび磁気センサの製造方法

    大兼 幹彦, 赤松 昇馬, 安藤 康夫, 熊谷 静似

    産業財産権の種類: 特許権

  11. 磁気センサおよびその製造方法

    古市 喬干, 吉村 政洋, 阿部 竜一郎, 与倉 久則, 薬師寺 啓, 杉原 敦, 福島 章雄, 湯浅 新治, 大兼 幹彦, 安藤 康夫, 角田 匡清

    産業財産権の種類: 特許権

  12. トンネル磁気抵抗素子およびトンネル磁気抵抗センサ

    藤原 耕輔, 熊谷 静似, 安藤 康夫, 大兼 幹彦

    産業財産権の種類: 特許権

  13. トンネル磁気抵抗センサ

    サブリ チャキル, 藤原 耕輔, 熊谷 静似, 安藤 康夫, 大兼 幹彦

    産業財産権の種類: 特許権

  14. トンネル磁気抵抗センサおよびその製造方法

    中野貴文, 藤原耕輔, 熊谷静似, 松﨑斉, 安藤康夫, 大兼幹彦

    産業財産権の種類: 特許権

  15. 磁化率測定装置及び磁化率測定方法

    アルマダウィミフタ, 大兼幹彦

    産業財産権の種類: 特許権

  16. 検査装置、検査方法及び検査プログラム

    伊藤淳, 大兼幹彦

    産業財産権の種類: 特許権

  17. 磁気センサー加工方法

    藤原耕輔, 安藤康夫, 大兼幹彦

    産業財産権の種類: 特許権

  18. トンネル磁気抵抗素子と磁化方向補正回路

    藤原耕輔, 安藤康夫, 大兼幹彦

    産業財産権の種類: 特許権

︎全件表示 ︎最初の5件までを表示

共同研究・競争的資金等の研究課題 15

  1. スピンエレクトロニクス材料探索およびデバイス作製技術開発 競争的資金

    制度名:Grant-in-Aid for Scientific Research

    1998年4月 ~ 継続中

  2. 音波を使用した液中非破壊検査

    2023年4月 ~ 2026年3月

  3. Sensoron: Fusing Memory and Computing into Spintronics-based Sensors

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    研究種目:Grant-in-Aid for Scientific Research (B)

    研究機関:Tohoku University

    2022年4月1日 ~ 2025年3月31日

  4. スピントロニクスセンサによる低周波電磁波を活用したスマートインフラ検査技術の開発

    2023年6月 ~ 2025年3月

  5. 量子スピントロニクス脳磁計の開発

    大兼幹彦

    2022年5月 ~ 2023年3月

  6. 規則合金系ヘテロ接合における多彩な物理現象とスピンデバイス創製

    安藤 康夫, 大兼 幹彦, 永沼 博, 水上 成美

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

    研究種目:Grant-in-Aid for Scientific Research (S)

    研究機関:Tohoku University

    2012年5月31日 ~ 2017年3月31日

    詳細を見る 詳細を閉じる

    大きな磁気異方性と小さな磁気緩和定数を示し、平坦性の良いL10構造MnAl薄膜の作製に成功した。高いスピン分極率と小さい磁気緩和定数を示すCoFeMnSiホイスラー合金を、アモルファスのSiO2基板上に作製することができた。L10-FePd電極上に極薄のPd薄膜を挿入し,成膜温度を最適化することでエピタキシャル成長したトンネル絶縁層を作製することができた。極薄かつ高品質のBiフェライト薄膜をLaSrMnO3強磁性層上に作製することに成功した。 以上の規則合金を用いたヘテロ接合は、従来のスピンデバイスの性能を凌駕し、多彩な物理現象を示すことから、全く新しいスピンデバイスの創成につながるものである。

  7. L10合金/ホイスラー合金積層電極を用いた高出力・低消費電力磁気抵抗素子の創製

    大兼 幹彦

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2012年4月1日 ~ 2015年3月31日

    詳細を見る 詳細を閉じる

    L10規則構造を有するMn系垂直磁化薄膜を作製し,高磁気異方性と低磁気緩和定数を兼ね備える強磁性体薄膜を得ることに成功した.さらに,得られたMn系垂直磁化薄膜と極薄の強磁性薄膜およびホイスラー合金を積層した電極を用いたトンネル磁気抵抗素子を作製した.その結果,Mn系垂直磁化薄膜を用いたトンネル磁気抵抗素子において世界で初めての磁気抵抗効果の観測に成功した.また,ホイスラー合金を電極としたCPP-GMR素子を作製し,室温で80%の世界最高の磁気抵抗比を観測することに成功した.さらに,スピン注入磁化反転の観測にも成功し,開発した磁気抵抗素子の有用性を明らかにした.

  8. 負のスピン分極材料の磁気緩和制御と高効率微細スピン注入源への新展開

    磯上 慎二, 角田 匡清, 大兼 幹彦, 佐久間 昭正

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)

    研究種目:Grant-in-Aid for Young Scientists (B)

    研究機関:Fukushima National College of Technology

    2012年4月1日 ~ 2015年3月31日

    詳細を見る 詳細を閉じる

    負のスピン分極材料であるFe4N薄膜を用いた高効率スピン注入源の開発を目的として研究を行った.窒素とアルゴンの混合ガスによる反応性スパッタリング法と赤外線集光加熱プロセスを用いて,高品質Fe4N/Pt接合膜試料の作製に成功した.Fe4NからのスピンポンピングによってPt薄膜で発生するインバーススピンホール起電力は,従来使用されてきたNiFeなどの強磁性膜に比べて約1桁高い値を示すことを見出した.これはスピン流生成効率において負のスピン分極材料を用いたFe4N/Pt系の優位性を示唆している.

  9. 垂直磁化トンネル接合の創製とスピン注入磁化反転

    宮崎 照宣, 水上 成美, 大兼 幹彦

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2009年 ~ 2011年

    詳細を見る 詳細を閉じる

    将来の高密度磁気メモリ対応のメモリセル材料を開発することを目的とし、単結晶Mn_xGa_<1-x>(0. 5≦x≦0. 75)合金薄膜について、メモリセルとして必要な磁気特性(飽和磁化M_s、垂直磁気異方性Kuおよびギルバードダンピング定数.)を調べた。M_sはxの増加に伴って600emu/ccから200emu/ccに直線的に減少した。これに対してK_uの減少はわずかで、15Merg/ccから10Merg/ccの変化である。ダンピング定数. はMn_<1. 54> Ga(Mn_<2. 12> Ga)の組成で0. 08 (0. 015)であった。これ等の特性はメモリ材料として要求される特性を満足している、 更に、Mn-Ga 合金膜を電極としたトンネル接合を作製し、10 Kと300 Kで磁気抵抗効果(TMR)を調べた。Mn-Ga 電極とトンネル障壁(MgO)の間に僅かのFe(Co)を挿入することにより、室温で60(40)%のTMR 比を得た。この値については更に向上させる必要がある。

  10. 金属系ナノヘテロ接合におけるスピン波励起と高周波デバイスの創製

    安藤 康夫, 大兼 幹彦, 水上 成美, 永沼 博

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2008年 ~ 2010年

    詳細を見る 詳細を閉じる

    Si基板上にボトムフリー層構成の面直通電型磁気抵抗(CPP-GMR)ナノヘテロ構造素子を作製し、スピン注入自励発振の測定を行った。磁場の印加方向を容易軸と90度とし、印加電流が3mA~7mAのときに発振強度が大きくなり、半値幅も減少した。また、下部自由層が連続した擬ポイントコンタクト型CPP-GMR素子を設計・作製した。50Ω整合のとれたコプレーナーウェーブガイドを独自に設計し、高周波伝達損失を10%まで低減させることに成功した。

  11. 金属系多層膜におけるスピン流と磁気緩和の光学的検出

    安藤 康夫, 大兼 幹彦, 水上 成美, 永沼 博

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas

    研究種目:Grant-in-Aid for Scientific Research on Priority Areas

    研究機関:Tohoku University

    2007年 ~ 2010年

    詳細を見る 詳細を閉じる

    強磁性金属に対しパルスレーザー光を照射した際にサブピコ秒領域で発生する減磁現象について、ホイスラー合金を中心に調べた。Mn-Ga合金並びにCo系垂直磁化膜の超高速減磁時間τは励起レーザー強度Pに対し増大する傾向を示し、微視的な理論と傾向が一致した。他方、AgやCr下地上に積層したCo_2MnSiホイスラー合金のτはPに対し減少する傾向を示した。

  12. ハーフメタルスピンスイッチの開発と論理回路への応用

    大兼 幹彦

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

    研究種目:Grant-in-Aid for Young Scientists (A)

    研究機関:Tohoku University

    2008年 ~ 2009年

    詳細を見る 詳細を閉じる

    Co_2MnSi組成ベースのハーフメタルホイスラー合金電極と酸化マグネシウムを用いたトンネル接合素子において,低温において1275%,室温において350%の磁気抵抗比を得ることに成功した.この磁気抵抗比はハーフメタル電極を用いたトンネル接合で世界最高であり,論理回路に応用可能なスイッチ素子が作製できた.開発した素子を微細加工によって直列接続した回路において,電圧を印加することで磁気抵抗比を大きく変化させることに成功した.このことによって,開発した素子が論理回路に応用できる可能性を示した.

  13. ハーフメタル・ナノスピントランジスタの開発

    大兼 幹彦

    2006年 ~ 2007年

    詳細を見る 詳細を閉じる

    1.ホイスラ合金を用いた高TMR素子の作製 これまでは,アモルファス構造のA1-Oを絶縁層として用いていたが,今年度は,結晶質のMgOを絶縁層に用いたCo_2MnSi/MgO/CoFe-TMR素子において,前年度を上回る,217%(室温),753%(低温)のTMR比を観測することに成功した.観測したTMR比はホイスラー合金を電極に用いたTMR素子において世界最高の値である.また,コンダクタンス特性の測定結果から,コヒーレントトンネリングが巨大TMR比の起源であることが示唆された。 2.ハーフメタル・スピントランジスタへの微細加工 作製したCo_2MnSi/MgO/Co_2MnSiTMR素子を前年度に確立した微細加工プロセスを用いてトランジスタ形状に微細加工した.加工後のTMR比は低温で270%であり,加工によるダメージがほとんどないことが分かった.さらに,ゲート電圧を印加して,ソース-ドレイン間の電流-電圧特性を測定した結果,ハーフメタルギャップエネルギー(〜150mV)以上のゲート電圧を加えると,ソース・ドレイン電流が大きく変化する現象が観測された.この動作は,考案当初に期待していたものと同様であり,ハーフメタルを用いたスピントランジスタ動作を初めて実証したものである. 3.ハーフメタル・スピントランジスタの高性能化のためのホイスラー合金材料探索 これまでに開発を行なってきたCo_2MnSi組成に加えて,今年度は,Co_2FeSi,Co_2CrSiの開発を行なった.その結果,前年度まで開発を進めていたCo_2MnSiを用いたTMR素子が最も高性能であることを明らかにした.

  14. ホイスラー合金を用いた高トンネル磁気低抗素子の創製とスピン注入磁化反転

    宮崎 照宣, 安藤 康夫, 久保田 均, 水上 成美, 大兼 幹彦

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2005年 ~ 2007年

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    1.エピタキシャルホイスラー系合金電極トンネル接合の作製 高品位なホイスラー合金電極と結晶質の酸化マグネシウムを組み合わせたCo_2MnSi/MgO/CoFe-トンネル接合において,217%(室温),753%(低温)の巨大なTMR比を観測することに成功した.このTMR比はホイスラー合金を用いたトンネル接合において世界最高の値である.また,このTMR接合のコンダクタンス特性を詳細に調べた結果,巨大TMR比の原因は結晶質のMgO絶縁層を介したコヒーレントトンネリング過程によるものと示唆された. 2.微細化とスピン注入磁化反転 磁化反転層に(Co_<50>Fe_<50>)_<100-x>B_x(x=20,25,30,膜厚d=2nm)を用いたCoFeB/MgO/CoFeB接合を作製し,スピン注入磁化反転の観測に成功した.その結果,反転電流密度は理論予測どおり,強磁性層の飽和磁化,ダンピング定数およびスピン分極率に依存することが明らかとなり,飽和磁化およびダンピング定数の低減が反転電流密度を低減するために非常に有効であることが分かった. 3.ダンピング定数αに関して 強磁性共鳴を用いて,種々の強磁性体のダンピング定数を系統的に明らかにした.さらに,トンネル接合構造における磁化反転層のダンピング定数を測定する方法を世界で初めて確立した.その結果,2nm程度の非常に薄いCoFeB磁化反転層のダンピング定数は,バルクの約5倍程度増大することが分かった.また,磁化反転層の隣接層がダンピング定数に大きな影響を及ぼすことを明らかにした.

  15. 微小強磁性トンネル接合のスピンダイナミクス

    大兼 幹彦, 安藤 康夫, 久保田 均, 水上 成美, 宮崎 照宣, 大兼 幹彦

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2003年 ~ 2005年

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    1.微細加工技術を用いたナノ領域への高密度スピン注入 (1)収束イオンビームおよび電子線リソグラフィを用い,絶縁層にMgOを用いることにより,最小100x200nm^2のトンネル微小接合を作製し,抵抗x面積値6Ωμm^2,磁気抵抗比90%を得た. (2)上記素子においてスピン注入磁化反転を観測することに成功した.反転に要した電流密度は7.7x10^6A/cm^2であり,熱処理温度の上昇とともに反転電流は増大した. 2.素子界面におけるスピン緩和 (1)強磁性体(FeNi)/非磁性体(Cu, Ru, Pt),および,FeNi/Cu/Pt積層膜の強磁性共鳴スペクトルを測定し,共鳴線幅より緩和時間およびスピン拡散長を見積もった.Cu内におけるスピン拡散長は室温で約350nm,液体ヘリウム温度で約1000nmであることがわかった. (2)強磁性体(FM)/Cu/CoFe積層膜の強磁性共鳴スペクトルを測定し,それぞれの磁性体の共鳴線幅の増大率を測定した.FMがCoFeBの場合,CoFeの線幅は大きく上昇しCoFeBの線幅の増大率は小さかった. 3.コプレーナ線路からの高速パルス磁界応答信号測定 (1)トンネル接合においてパルス電流を用いたスピン注入磁化反転の応答信号測定システム(パルス幅が1μs,パルス電流の最大値が20mA)を製作した.また,トンネル接合の反転電流のパルス幅依存性を調べ,パルス幅の減少により反転電流が増大することを実験的に明らかにした. (2)500psよりも更に速い時間スケールの磁化の変動を測定するため,ポンププローブ測定が可能な光学系を構築した.180x90μm^2のパーマロイ薄膜の磁化の才差運動によるシグナルを測定し,ダンピング定数α=0.008を得た. (3)積層フェリ構造の磁性層のダンピング定数はFeNi単層膜と比較して増大することを明らかにした.

︎全件表示 ︎最初の5件までを表示

担当経験のある科目(授業) 9

  1. 電磁気学II

  2. 物性物理学原論

  3. 先端スピン工学特論

  4. ナノ構造制御工学

  5. 磁性物理学

  6. 学生実験

  7. 物理学A

  8. 界面物理学

  9. 電磁気学I

︎全件表示 ︎最初の5件までを表示

その他 25

  1. スピントロニクス学術研究基盤と連携ネットワーク拠点

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    スピントロニクス学術研究基盤と連携ネットワークの構築

  2. 学際研究重点プログラム

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    原子内包フラーレンナノバイオトロニクスの創成

  3. TMR素子のセンサ応用研究

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    リニア出力型TMR磁気センサの研究 ‐ 垂直磁場印加型構造の出力リニアリティとダイナミックレンジの特性検証 -

  4. 低RA・高スピン偏極ソース/ドレイン電極の開発

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    スピンFET実現のための低RA・高スピン偏極ソース/ドレイン電極を開発する

  5. JSPS Core-to-Coreプロジェクト

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    次世代スピントロニクス素子の作製と評価

  6. 産学コンソーシアム運営事業

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    強磁性トンネル接合素子を用いた高感度磁気センサの研究開発

  7. 文部科学省 次世代IT基盤構築のための研究開発

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    耐災害性に優れた安心・安全社会のためのスピントロニクス材料およびデバイス基盤技術の研究開発を行う

  8. JST復興促進プログラム(A-STEP) ハーフメタル合金薄膜作製のための超高真空加熱・成膜制御システムの開発

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    ハーフメタル合金は、電気伝導を担う電子スピンが完全にスピン偏極することが期待され、スピントロニクス分野において非常に大きな注目を集めている。特に、東北大学の大兼准教授のグループでは、ハーフメタル合金薄膜を利用した、高品位なスピントロニクス素子の開発に成功しており、磁気メモリ、HDDヘッド、生体磁気センサー、スピントランジスタ等の画期的素子への応用が期待されている。しかし、現在の素子作製プロセスは、良質な素子を作製可能である反面、生産プロセスに適合したものではない。本提案は、ハーフメタルを用いた素子を製品化するために必要不可欠な、短時間で高品位な素子を得るための超高真空加熱・成膜制御システムを開発することを目的としたものである。

  9. トンネル磁気抵抗素子を用いた心磁図および脳磁図と核磁気共鳴像の室温同時測定装置の開発

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    強磁性トンネル接合を用いた微小モジュールを配置した室温動作の脳磁計、心磁計の開発

  10. JST産学共創基礎基盤研究プログラム

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    高品位モデル磁石の高精度磁気特性および構造評価

  11. ハーフメタルホイスラー合金を用いた巨大磁気抵抗素子における磁気抵抗効果の結晶面方位依存性に関する研究

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    次世代のハードディスク用読み取りヘッドとして、高磁気抵抗比と低素子抵抗値を兼ね備えた、面直通電型巨大磁気抵抗 (CPP-GMR) 素子に対する期待が大きい。伝導電子が完全にスピン分極したハーフメタル材料をCPP-GMR素子の電極に用いれば、飛躍的に磁気抵抗比を向上させることが原理的に可能である。本研究では、ハーフメタル材料としてホイスラー合金を用い、種々の結晶面方位を有するフルエピタキシャルCPP-GMR素子を開発する。結晶面方位と磁気抵抗効果の関係を明らかにし、70~100%の高磁気抵抗比を実現するための明確な指針を得ることが本研究の目的である。

  12. 先端スピントロニクス材料と伝導現象(ASPIMATT)

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    新材料によりもたらされる新規の伝導現象を実現することを主目的とし、新材料を用いたトンネル磁気抵抗(TMR)素子および巨大磁気抵抗(GMR)素子に加えて、ローカル/ノンローカル面内スピン伝導、スピンホール効果およびマグノンによる角運動量伝導のような新しいタイプのスピントロニクスデバイスの創成を目指す。

  13. 最先端研究開発支援プログラム

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    省エネルギー・スピントロ二クス論理集積回路の研究開発

  14. Design of Materials and Structures for Reduction in Spin Transfer Noise for Heusler Alloy Based CPP GMR Structures

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    ホイスラー合金を用いたHDD用CPP-GMR素子の作製と評価に関する研究

  15. 超微小サイズ不揮発性MRAM素子の性能評価

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    CoPt微粒子を磁化反転層とした超微少MRAM素子を作製し,伝導性AFM装置を用いてその評価を行なう研究で,提案研究とは全く異なる。

  16. 二国間交流事業

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    日本-中国の二国間で強磁性トンネル接合および二重強磁性トンネル接合の開発を行なう。

  17. 巨大トンネル磁気抵抗素子を用いた超高感度磁界センサーの開発

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    巨大な磁気抵抗効果を示すトンネル接合素子を超高感度な磁界センサーに応用する研究である。磁界センサーの性能を示す,単位磁界あたりの抵抗変化率が20%/Oe以上の高性能トンネル接合を作製し,磁界センサー回路を試作する。本事業期間中にナノテスラオーダーの磁界検出を実証し,製品化に向けた研究開発へと向かう。さらに,超伝導量子干渉素子 (SQUID) クラスの超高感度磁界検出の実現可能性を明らかにする。

  18. 数Tbit/inch2磁気記録密度実現のためのオールホイスラー合金磁気抵抗素子の開発

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    非磁性のホイスラー合金を中間層とした面直通電型GMR素子を作製し,磁気ヘッドへの応用を目指すものである。本提案の超高感度センサーと異なり,比較的低感度であっても,ヘッドの回路に適合する極めて低抵抗のGMR素子を作製するための研究である。

  19. JST 戦略的国際科学協力推進事業 高スピン分極率を有するホイスラー合金に関する研究

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    日本側の優れたホイスラー合金作製技術とドイツ側の高度なスピンダイナミクス測定技術を融合し,新たな物理現象,デバイスを創出する為の研究

  20. 文部科学省 高機能・超低消費電力スピンデバイス・ストレージ基盤技術の開発

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    世界をリードするナノスピン材料創成・磁性体極微細加工技術の研究開発を基軸に,スピンデバイスを活用する革新的な高速・不揮発性メモリインロジック(電力/速度比1/1000以下)とテラビット級次世代垂直記録技術による超高速大容量ストレージシステム(電力/容量比1/20以下,どちらも従来技術の延長と比較)を開発し,次世代の高機能・超低消費電力コンピューティングデバイス・システムの基盤技術を確立する.

  21. NEDO スピントロニクス不揮発性機能技術プロジェクト

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    スピントロニクス技術が秘める不揮発性機能をはじめとする情報通信分野における革新的諸機能を実現するための基盤技術の確立、並びに、実用化に向けたデバイス技術の研究開発

  22. 次世代スピンデバイス創生のためのハーフメタル強磁性トンネル接合の開発

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    電子の電荷とスピンの二つの自由度を積極的に利用する”スピンエレクトロニクス”が、次世代情報化社会の中で果たす役割は非常に大きい。不揮発性磁気メモリ(MRAM)を始めとして、スピンデバイスの研究開発は急速に進展しており、また、次世代の全く新しいスピンデバイスも種々考案されている。それぞれのスピンデバイスに求められる材料、素子特性はデバイスごとに異なるが、あらゆるスピンデバイスに共通して求められるものは、”高スピン分極率を有する強磁性体材料”である。本研究では、ハーフメタル強磁性体 (スピン分極率100 %) である”ホイスラー合金材料”の開発を行い、それを用いた”巨大なトンネル磁気抵抗比を示す素子”作製技術の確立を目指す。

  23. 共鳴磁気トンネル・ナノドット不揮発性メモリの創製

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    本研究は、代表者が提案した共鳴磁気トンネル・ナノドット不揮発性メモリを実現し、その動作を確認し、それを用いた新しいメモリ回路の可能性を示すことを目的としている。SAND 法と呼ぶ新しい膜形成手法を用いて、ドット粒径が1~3nm で、従来より約1 桁高いドット密度(2×1013cm-2)をもつFePt ナノドットの形成に成功した。また、FePt ナノドットを浮遊ゲートとするMOS構造を用いて磁気トンネル・ナノドット不揮発性メモリの基本的な動作の確認にも成功している。

  24. 総務省SCOOPプログラム 超ギガビット磁気メモリの基盤技術の開発

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    超大容量磁気ランダムアクセスメモリ(MRAM)のための高性能材料の開発

  25. RR2002 ITプログラム 高機能・超低消費電力メモリの開発

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    大容量,高速,低消費電力の磁気ランダムアクセスメモリ(MRAM)の開発

︎全件表示 ︎最初の5件までを表示