顔写真

ナガヌマ ヒロシ
永沼 博
Hiroshi Naganuma
所属
国際集積エレクトロニクス研究開発センター 研究開発部門
職名
准教授
学位
  • 博士(工学)(大阪大学)

  • 修士(工学)(奈良先端科学技術大学院大学)

プロフィール

[2次元材料と規則合金の結合]
グラフェン、WS2, h-BNなどの二次元材料と高磁気異方性を有するL10規則合金材料の界面結合に関わる研究を行っている。

[強的秩序とその操作に関わる研究]
強誘電体およびマルチフェロイクスなど外場との相互作用の強い酸化物を用いた接合および界面を作製し、新しいスピン依存伝導現象、2次元電子ガスのスピン軌道相互作用を利用した高効率スピン-電荷変換に関わる研究を行っている。また、室温で動作する新規マルチフェロイックスの探索を行っている。

[高速スピンダイナミクス]
スピントランスファートルク、スピン軌道トルクなどを利用した高速スピンダイナミクスの研究を行っている。特に、高い結晶磁気異方性を有するL10規則合金を用いた強磁性トンネル接合素子において高周波スピンダイナミクスを電気的に検出し、不揮発性磁気メモリの高速動作時の物理的現象の理解および次世代の高周波スピン発振・検波の研究開発を行っている。

[STT, SOT-MRMA集積デバイス]
CMOSと3次元構造としたSTT, SOT-MRAM集積デバイスの実用化研究を行っている。サブナノ秒の高速磁化反転特性およびデータ熱安定性を300mmシリコンウェハー上に作製したSTT,SOT-MRAM素子を用いて評価している。また、マイクロマグネティックシミュレーションによる解析も行っている。

経歴 2

  • 2023年12月 ~ 継続中
    名古屋大学 未来材料・システム研究所 材料創製部門 特任准教授

  • 2023年12月 ~ 継続中
    名古屋大学 国際高等研究機構 特任准教授

委員歴 14

  • 次世代放射光施設利用推進委員会 マシンタイム管理検討専門委員会委員

    2021年12月 ~ 継続中

  • 東北大学 安全保障輸出管理委員会(全学)委員

    2021年4月 ~ 継続中

  • 公益社団法人応用物理学会 強的秩序とその操作に関わる研究会 代表

    2021年1月 ~ 継続中

  • J-PARC MLF 課題審査委員

    2020年4月 ~ 継続中

  • International conference on Solid State Devices and Materials Program committee member

    2020年4月 ~ 継続中

  • Futurer Materialz 顧問

    2019年1月 ~ 継続中

  • パリ異分野融合科学者の会 幹事

    2018年10月 ~ 継続中

  • 人工知能ワーキンググループ グループ長

    2018年9月 ~ 継続中

  • 応用物理学会「強的秩序とその操作に関わる研究グループ」 代表

    2015年9月 ~ 2020年10月

  • 日本磁気学会編集論文委員会 編集委員

    2013年4月 ~ 2019年3月

  • 応用物理学会東北支部 企画委員

    2012年7月 ~ 2016年3月

  • 誘電体スピントロニクス研究会 主査

    2015年1月 ~ 2015年8月

  • 応用物理学会東北支部 庶務幹事

    2012年1月 ~ 2013年1月

  • Bi系マルチフェロイクス研究会 主査

    2014年1月 ~

︎全件表示 ︎最初の5件までを表示

所属学協会 7

  • 公益社団法人応用物理学会「強的秩序とその操作に関わる研究会」

    2021年1月 ~ 継続中

  • 公益財団法人応用物理学会「強的秩序とその操作に関わる研究グループ」

    2015年1月 ~ 2020年12月

  • 応用物理学会

  • IEEE membership

    2019年4月 ~ 継続中

  • MRS

  • 日本金属学会

  • 日本磁気学会

︎全件表示 ︎最初の5件までを表示

研究キーワード 7

  • 集積デバイス

  • 人工知能

  • 強的秩序とその操作

  • 酸化物エレクトロニクス

  • 薄膜

  • マルチフェロイクス

  • スピントロニクス

研究分野 8

  • 情報通信 / 計算科学 /

  • ナノテク・材料 / 複合材料、界面 /

  • ものづくり技術(機械・電気電子・化学工学) / 電気電子材料工学 /

  • ものづくり技術(機械・電気電子・化学工学) / 電子デバイス、電子機器 / 不揮発性磁気メモリ

  • ナノテク・材料 / 薄膜、表面界面物性 /

  • ナノテク・材料 / 応用物性 / スピントロニクス

  • ナノテク・材料 / 金属材料物性 / 強磁性トンネル接合

  • 情報通信 / 知能情報学 /

受賞 11

  1. 第82回応用物理学会秋季学術講演会 ポスター賞

    2021年9月 公益社団法人応用物理学会 グラフェン/L10-規則合金界面に誘起された異方的軌道モーメント

  2. フロンティア材料研究所学術賞

    2020年7月 フロンティア材料研究所 ペロブスカイトエピタキシャル膜の構造解析と界面キャリア注入効果

  3. ポスター賞

    2019年3月 公益社団法人応用物理学会 Increase of Fe Magnetic moment of BiFeO3 in Co/BiFeO3/LaSrMnO3 tunnel junctions

  4. 日本応用磁気学会 優秀講演賞受賞

    2007年9月1日 日本応用磁気学会

  5. ポスター賞

    2021年10月 The 5th symposium for the core research clusters for materials science and spintronics

  6. 2013年度第15回田中貴金属 MMS賞

    2014年3月31日 田中貴金属

  7. 貴金属に関わる研究助成金 シルバー賞

    2013年1月 田中貴金属工業

  8. Virtual Journal of Nanoscale Science & Technology

    2012年1月 AIP

  9. 応用物理学会論文賞

    2011年9月11日 応用物理学会

  10. 2011年度田中貴金属MMS賞

    2011年5月31日 田中貴金属工業

  11. 2009年度田中貴金属シルバー賞

    2009年1月29日 田中貴金属工業

︎全件表示 ︎最初の5件までを表示

論文 250

  1. Ultrafast spin–orbit torque-induced magnetization switching in a 75°-canted magnetic tunnel junction

    T. V. A. Nguyen, H. Naganuma, H. Honjo, S. Ikeda, T. Endoh

    AIP Advances 2024年2月1日

    DOI: 10.1063/9.0000789  

  2. First-principle study of spin transport property in L10-FePd(001)/graphene heterojunction

    Hayato Adachi, Ryusuke Endo, Hikari Shinya, Hiroshi Naganuma, Tomoya Ono, Mitsuharu Uemoto

    Journal of Applied Physics 2024年1月28日

    DOI: 10.1063/5.0175047  

  3. Twist p<sub><i>z</i></sub> Orbital and Spin Moment of the Wavy-Graphene/<i>L</i>1<sub>0</sub>-FePd Moiré Interface 査読有り

    H. Naganuma, M. Uemoto, H. Adachi, H. Shinya, I. Mochizuki, M. Kobayashi, A. Hirata, B. Dlubak, T. Ono, P. Seneor, J. Robertson, K. Amemiya

    The Journal of Physical Chemistry C 127 11481-11489 2023年6月9日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.2c08982  

    ISSN:1932-7447

    eISSN:1932-7455

  4. Spintronics memory using magnetic tunnel junction for X nm-generation 招待有り 査読有り

    Hiroshi Naganuma

    Japanese Journal of Applied Physics 62 SG0811-1-SG0811-17 2023年6月1日

    DOI: 10.35848/1347-4065/accaed  

  5. Comparing h-BN and MgO tunnel barriers for scaled magnetic tunnel junctions 招待有り 査読有り

    J. Robertson, H. Naganuma, H. Lu

    Japanese Journal of Applied Physics 63 SC0804-1-SC0804-8 2023年4月1日

    DOI: 10.35848/1347-4065/acb062  

  6. Insight into the mechanism of bidirectional magnetoelectric effects unveil cycloidal/uncompensated hybrid antiferromagnetic multiferroics 査読有り

    Tomohiro Ichinose, Hiroshi Naganuma

    Physical Review Materials 7 014405-1-014405-12 2023年1月17日

    DOI: 10.1103/PhysRevMaterials.7.014405  

  7. Influence of sidewall damage on thermal stability in quad-CoFeB/MgO interfaces by micromagnetic simulation 査読有り

    Hiroshi Naganuma, Hiroaki Honjo, Chikako Kaneta, Koichi Nishioka, Shoji Ikeda, Tetsuo Endoh

    AIP Advances 12 (12) 25317-1-25317-10 2022年12月21日

    出版者・発行元:None

    DOI: 10.1063/5.0112741  

    eISSN:2158-3226

  8. 25 nm iPMA-type Hexa-MTJ with solder reflow capability and endurance>107 for eFlash-type MRAM 査読有り

    H. Honjo, K. Nishioka, S. Miura, H. Naganuma, T. Watanabe, T. Nasuno, T. Tanigawa, Y. Noguchi, H. Inoue, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE International electron devices meeting 226-229 2022年12月

    DOI: 10.1109/IEDM45625.2022.10019412  

  9. Ferromagnetic Electrodes of Ferromagnetic Tunnel Junctions 査読有り

    Hiroshi Naganuma

    Journal of the institute of electronics, information and communication engineering 105 (12) 1414-1420 2022年12月

  10. Density functional study of twisted graphene <i>L</i>1<sub>0</sub>-FePd heterogeneous interface

    Mitsuharu Uemoto, Hayato Adachi, Hiroshi Naganuma, Tomoya Ono

    Journal of Applied Physics 132 (9) 095301-1-095301-11 2022年9月7日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0101703  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Graphene on [Formula: see text]-FePd(001), which has been experimentally studied in recent years, is a heterogeneous interface with a significant lattice symmetry mismatch between the honeycomb structure of graphene and tetragonal alloy surface. In this work, we report on the density functional study of its atomic-scale configurations, electronic and magnetic properties, and adsorption mechanism, which have not been well understood in previous experimental studies. We propose various atomic-scale models, including simple nontwisted and low-strain twisted interfaces, and analyze their energetical stability by performing structural optimizations using the van der Waals interactions of both DFT-D2 and optB86b-vdW functionals. The binding energy of the most stable structure reached [Formula: see text] eV/atom for DFT-D2 ([Formula: see text] eV/atom for optB86b-vdW). The calculated FePd-graphene spacing distance was approximately 2 Å, which successfully reproduced the experimental value. We also find out characteristic behaviors: the modulation of [Formula: see text]-bands, the suppression of the site-dependence of adsorption energy, and the rise of moiré-like corrugated buckling. In addition, our atomic structure is expected to help build low-cost computational models for investigating the physical properties of [Formula: see text] alloys/two-dimensional interfaces.

  11. Influence of Iridium Sputtering Conditions on the Magnetic Properties of Co/Pt-Based Iridium-Synthetic Antiferromagnetic Coupling Reference Layer

    H. Honjo, H. Naganuma, K. Nishioka, T. V. A. Nguyen, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE Transactions on Magnetics 58 (8) 1400305-1-1400305-5 2022年8月

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

    DOI: 10.1109/tmag.2022.3151562  

    ISSN:0018-9464

    eISSN:1941-0069

  12. Effect of oxygen incorporation on dynamic magnetic properties in Ta-O/Co-Fe-B bilayer films under out-of-plane and in-plane magnetic fields 査読有り

    T. V. A. Nguyen, Y. Saito, H. Naganuma, S. Ikeda, T. Endoh, Y. Endo

    AIP Advances 12 (3) 035133-035133 2022年3月15日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/9.0000297  

    eISSN:2158-3226

    詳細を見る 詳細を閉じる

    Dynamic magnetic properties of Ta-O/Co<sub>20</sub>Fe<sub>60</sub>B<sub>20</sub> bilayer films are strongly influenced by the oxidation condition of the Ta-O layer. The oxidation of the Ta-O layer by a slight amount of oxygen with a pressure ( P<sub>Oxygen</sub>) of 0.03 Pa decreases in-plane damping constant ( α<sub>IP</sub>), and increases the effective magnetization (4π M<sub>s,eff</sub>). Then, both α<sub>IP</sub> and 4π M<sub>s,eff</sub> maintain their values by increasing P<sub>Oxygen</sub> up to 0.3 Pa. The out-of-plane damping constant ( α<sub>OP</sub>) showed a similar tendency to that of α<sub>IP</sub> against P<sub>Oxygen</sub>, although α<sub>OP</sub> is much smaller than α<sub>IP</sub> in every P<sub>Oxygen</sub>. α<sub>OP</sub> reaches to 0.0033 for sample oxidized at 0.03 Pa. It was suggested that α<sub>IP</sub> consists of both the intrinsic damping and the extrinsic damping, while α<sub>OP</sub> is closer to the intrinsic damping. The control of α<sub>OP</sub> and α<sub>IP</sub> by the oxidation would be beneficial in designing the high frequency spintronic devices.

  13. Unveiling a Chemisorbed Crystallographically Heterogeneous Graphene/L10‑FePd Interface with a Robust and Perpendicular Orbital Moment 国際誌 査読有り

    Hiroshi Naganuma, Masahiko Nishijima, Hayato Adachi, Mitsuharu Uemoto, Hikari Shinya, Shintaro Yasui, Hitoshi Morioka, Akihiko Hirata, Florian Godel, Marie-Blandine Martin, Bruno Dlubak, Pierre Seneor, Kenta Amemiya

    ACS Nano 16 4139-4151 2022年2月28日

    DOI: 10.1021/acsnano.1c09843  

  14. Effect of Magnetic Coupling Between Two CoFeB Layers on Thermal Stability in Perpendicular Magnetic Tunnel Junctions with MgO/CoFeB/Insertion Layer/CoFeB/MgO Free Layer 査読有り

    Nishioka, S. Miura, H. Honjo, H. Naganuma, T. V. A. Nguyen, T. Watanabe, S. Ikeda, T. Endoh

    IEEE Transaction on magnetics 58 4400406-1-4400406-6 2022年1月21日

    出版者・発行元:None

    DOI: 10.1109/tmag.2021.3083575  

    ISSN:0018-9464

    eISSN:1941-0069

  15. Perpendicular Magnetic Tunnel Junctions with Four Anti-ferromagnetically Coupled Co/Pt Pinning Layers 査読有り

    H. Honjo, K. Nishioka, S. Miura, H. Naganuma, T. Watanabe, Y. Noguchi, T. V. A. Nguyen, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE. Transaction on Magnetics 58 4400105-1-4400105-5 2022年1月21日

    出版者・発行元:None

    DOI: 10.1109/tmag.2021.3078710  

    ISSN:0018-9464

    eISSN:1941-0069

  16. High-quality sputtered BiFeO3 for ultra-thin epitaxial films 査読有り

    Tomohiro Ichinose, Daisuke Miura, Hiroshi Naganuma

    ACS Applied Electric Materials 3 4836-4848 2021年11月8日

    出版者・発行元:None

    DOI: 10.1021/acsaelm.1c00688  

    ISSN:2637-6113

    eISSN:2637-6113

  17. Comparison of hexagonal boron nitride and MgO tunnel barriers in Fe,Co magnetic tunnel junctions 査読有り

    H. Lu, J. Robertson, H. Naganuma

    Applied Physics Reviews 8 031307-1-031307-14 2021年9月

    DOI: 10.1063/5.0049792  

  18. Advanced 18 nm Quad-MTJ technology overcomes dilemma of Retention and Endurance under Scaling beyond 2X nm 査読有り

    H. Naganuma, S. Miura, H. Honjo, K. Nishioka, T. Watanabe, T. Nasuno, H. Inoue, T. V. A. Nguyen, Y. Endo, Y. Noguchi, M. Yasuhira, S. Ikeda, T. Endoh

    VLSI Technology Digest T0179 2021年6月

    ISSN:0743-1562

  19. First demonstration of 25 nm Quad interface p-MTJ device with low resistance-area product MgO and 10years retention for high reliable STT-MRAM 査読有り

    K. Nishioka, S. Miura, H. Honjo, H. Inoue, T. Watanabe, T. Nasuno, H. Naganuma, T. V. A. Nguyen, Y. Noguchi, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE Transaction on Electron Devices 68 (6) 2680-2685 2021年5月3日

    DOI: 10.1109/TED.2021.3074103  

    ISSN:0018-9383

    eISSN:1557-9646

  20. Enhancement of magnetic coupling and magnetic anisotropy in MTJs with multiple CoFeB/MgO interfaces for high thermal stability 査読有り

    K. Nishioka, H. Honjo, H. Naganuma, T. V. A. Nguyen, M. Yasuhira, S. Ikeda, T. Endoh

    AIP Advances 11 (2) 025231-025231 2021年2月12日

    出版者・発行元:{AIP} Publishing

    DOI: 10.1063/9.0000048  

    ISSN:2158-3226

  21. Effect of surface modification treatment on top-pinned MTJ with perpendicular easy axis

    Hiroaki Honjo, Hiroshi Naganuma, T. V. A. Nguyen, H. Inoue, M. Yasuhira, Shoji Ikeda, Tetsuo Endoh

    AIP Advances 11 (2) 025211-1-025211-5 2021年2月3日

    出版者・発行元:None

    DOI: 10.1063/9.0000047  

    eISSN:2158-3226

  22. Magnetic and ferroelectric properties of oxygen octahedron/tetrahedron mixed ultrathin multiferroic layer by oxygen desorption 査読有り

    T. Ichinose, H. Naganuma

    Journal of Applied Physics 129 (3) 034101-034101 2021年1月15日

    出版者・発行元:{AIP} Publishing

    DOI: 10.1063/5.0032428  

    ISSN:0021-8979 1089-7550

  23. First Demonstration of 25-nm Quad Interface p-MTJ Device With Low Resistance-Area Product MgO and Ten Years Retention for High Reliable STT-MRAM

    K. Nishioka, S. Miura, H. Honjo, H. Inoue, T. Watanabe, T. Nasuno, H. Naganuma, T. V. A. Nguyen, Y. Noguchi, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE Transactions on Electron Devices 1-6 2021年

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

    DOI: 10.1109/ted.2021.3074103  

    ISSN:0018-9383

    eISSN:1557-9646

  24. Scalability of Quad Interface p-MTJ for 1X nm STT-MRAM with 10 ns Low Power Write Operation, 10 years Retention and Endurance > 10^11 査読有り

    S. Miura, K. Nishioka, H. Naganuma, T. V. A. Nguyen, H. Honjo, S. Ikeda, T. Watanabe, H. Inoue, M. Niwa, T. Tanigawa, Y. Noguchi, T. Yoshiduka, M. Yasuhira, T. Endoh

    IEEE Transactions on Electron Devices 67 (12) 5368-5373 2020年11月26日

    出版者・発行元:None

    DOI: 10.1109/TED.2020.3025749  

    ISSN:0018-9383

    eISSN:1557-9646

  25. Flux-mediated doping of Bi into (La,Sr)MnO3 films grown on NdGdO3 (110) substrates 査読有り

    Mizufune, Koji, Naganuma, Hiroshi, Maruyama, Shingo, Matsumoto, Yuji

    ACS Applied Electronic Materials 2020年10月29日

    出版者・発行元:None

    DOI: 10.1021/acsaelm.0c00718  

    ISSN:2637-6113

    eISSN:2637-6113

  26. Micromagnetic simulation of the temperature dependence of the switching energy barrier using string method assuming sidewall damages in perpendicular magnetized magnetic tunnel junctions

    Hiroshi Naganuma, Hideo Sato, Shoji Ikeda, Tetsuo Endoh

    AIP Advances 2020年7月1日

    DOI: 10.1063/5.0007499  

  27. Micromagnetic simulation of the temperature dependence of the switching energy barrier using string method assuming side wall damages in perpendicular magnetized magnetic tunnel junctions 査読有り

    Hiroshi Naganuma, Hideo Sato, Shoji Ikeda, Tetsuo Endoh

    AIP Advanced 10 (7) 075106-1-075106-7 2020年7月

  28. Growth mechanism and domain structure study on epitaxial BiFeO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 査読有り

    In-Tae Bae, Shintaro Yasui, Tomohiro Ichinose, Mitsuru Itoh, Takahisa Shiraishi, Takanori Kiguchi, Hiroshi Naganuma

    Journal of Applied Physics 127 (24) 245303-245303 2020年6月28日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0005672  

    ISSN:0021-8979

    eISSN:1089-7550

  29. Influence of Hard Mask Materials on the Magnetic Properties of Perpendicular MTJs with Double CoFeB/MgO Interface 査読有り

    H. Honjo, M. Niwa, K. Nishioka, T. V. A. Nguye, H. Naganuma, Y. Endo, M. Yasuhira, S. Ikeda, T. Endoh

    IEEE. Transaction on Magnetics 56 6703504-11-6703504-4 2020年6月

  30. [Proceedings] Scalability of Quad Interface p-MTJ for 1X nm STT-MRAM with 10 ns Low Power Write Operation, 10 years Retention and Endurance > 10^11 査読有り

    S. Miura, K. Nishioka, H. Naganuma, T. V. A. Nguyen, H. Honjo, S. Ikeda, T. Watanabe, H. Inoue, M. Niwa, T. Tanigawa, Y. Noguchi, T. Yoshiduka, M. Yasuhira, and T. Endoh

    VLSI2020 TM2 - RRAM TM3.1-6 2020年6月

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

    DOI: 10.1109/ted.2020.3025749  

    ISSN:0018-9383

    eISSN:1557-9646

  31. A perpendicular graphene/ferromagnet electrode for spintronics 査読有り

    H. Naganuma, V. Zatko, M. Galbiati, F. Godel, A. Sander, C. Carrétéro, O. Bezencenet, N. Reyren, M.-B. Martin, B. Dlubak, P. Seneor

    Applied Physics Letters 116 (17) 173101-173101 2020年4月27日

    出版者・発行元:{AIP} Publishing

    DOI: 10.1063/1.5143567  

  32. (La<sub>0.3</sub>Sr<sub>0.7</sub>)(Al<sub>0.65</sub>Ta<sub>0.35</sub>)O<sub>3</sub>基板上にエピタキシャル成長させたBiFeO<sub>3</sub>膜の成長機構と強誘電体ドメイン構造

    In-Tae Bae, 安井 伸太郎, 一ノ瀬 智浩, 伊藤 満, 白石 貴久, 木口 賢紀, 永沼 博

    応用物理学会学術講演会講演予稿集 2020.1 1253-1253 2020年2月28日

    出版者・発行元:公益社団法人 応用物理学会

    DOI: 10.11470/jsapmeeting.2020.1.0_1253  

    eISSN:2436-7613

  33. Short range biaxial strain relief mechanism within epitaxially grown BiFeO3 国際誌 査読有り

    In-Tae Bae, Shintaro Yasui, Tomohiro Ichinose, Mitsuru Itoh, Takahisa Shiraishi, Takanori Kiguchi, Hiroshi Naganuma

    Scientific reports 9 (1) 6715-1-6715-10 2019年4月

    DOI: 10.1038/s41598-019-42998-x  

  34. Lattice mismatch effect on biaxial strain exerted on epitaxially-grown BiFeO<sub>3</sub>

    Naganuma Hiroshi, Bae In-Tae, Yasui Sintaro, Ito Mitsuru, Shiraishi Takahisa, Kiguchi Takanori, Ichinose Tomohiro

    JSAP Annual Meetings Extended Abstracts 2019.1 1215-1215 2019年2月25日

    出版者・発行元:The Japan Society of Applied Physics

    DOI: 10.11470/jsapmeeting.2019.1.0_1215  

    eISSN:2436-7613

  35. Tensile stress effect on epitaxial BiFeO3 thin film grown on KTaO3 査読有り

    In-Tae Bae, Tomohiro Ichinose, Myung-Geun Han, Yimei Zhu, Shintaro Yasui, Hiroshi Naganuma

    Scientific Reports 8 (1) 803-1-803-9 2018年12月1日

    出版者・発行元:Nature Publishing Group

    DOI: 10.1038/s41598-018-19487-8  

    ISSN:2045-2322

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    Comprehensive crystal structural study is performed for BiFeO3 (BFO) film grown on KTaO3 (KTO) substrate using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Nano-beam electron diffraction (NBED) combined with structure factor calculation and high resolution TEM images clearly reveal that the crystal structure within BFO thin film is rhombohedral BFO, i.e., bulk BFO phase. Epitaxial relationship found by NBED indicates the BFO film grows in a manner that minimizes lattice mismatch with KTO. It further suggests BFO film is under slight biaxial tensile stress (~0.35%) along in-plane direction. XRD reveals BFO lattice is under compressive stress (~1.6%), along out-of-plane direction as a result of the biaxial tensile strain applied along in-plane direction. This leads to Poisson's ratio of ~0.68. In addition, we demonstrate (1) why hexagonal notation rather than pseudocubic one is required for accurate BFO phase evaluation and (2) a new XRD method that shows how rhombohedral BFO can readily be identified among other phases by measuring a rhombohedral specific Bragg's reflection.

  36. Elucidation of crystal symmetry and strain of BiFeO<sub>3</sub> epitaxial films on various substrates by structural calculation and electron diffraction

    Naganuma Hiroshi, In-Tae Bae, Ichinose Tomohiro, Kovacs Andras, Yasui Shintaro, Zhao Hong, Iniguez Jorge, Han Myung-Geun

    JSAP Annual Meetings Extended Abstracts 2018.2 1305-1305 2018年9月5日

    出版者・発行元:The Japan Society of Applied Physics

    DOI: 10.11470/jsapmeeting.2018.2.0_1305  

    eISSN:2436-7613

  37. Structural analyses and first-principles simulation for new crystal symmetric BiFeO<sub>3</sub> grown on LaAlO<sub>3</sub> substrates

    Naganuma Hiroshi, Bae In-Tae, Kovacs Andras, Zhao Hong Jian, Iniguez Jorge, Yasui Shintaro, Ichinose Tomohiro

    JSAP Annual Meetings Extended Abstracts 2018.2 1335-1335 2018年9月5日

    出版者・発行元:The Japan Society of Applied Physics

    DOI: 10.11470/jsapmeeting.2018.2.0_1335  

    eISSN:2436-7613

  38. Thermooptic properties of epitaxial BiFeO<inf>3</inf> films with different orientations 査読有り

    Shima, H., Tsutsumi, K., Suzuki, M., Tadokoro, T., Naganuma, H., Okamura, S., Kamei, T.

    Japanese Journal of Applied Physics 57 (11) 11UF10-1-11UF10-5 2018年9月

    DOI: 10.7567/JJAP.57.11UF10  

  39. Manipulation of multi-degrees of freedom in ferroic-ordering FOREWORD 査読有り

    Naganuma, H., Fujisawa, H., Iijima, T.

    Japanese Journal of Applied Physics 57 (9) 1-1 2018年8月

    DOI: 10.7567/jjap.57.090201  

  40. Determination of rhombohedral structure of BiFeO3 single-domain-like films grown on SrTiO3 and LaAlO3 substrates by X-ray diffraction using (2(1)over-bar(3)over-bar)(hex) 査読有り

    Ichinose, T., Yasui, S., Bae, I. T., Naganuma, H.

    Japanese Journal of Applied Physics 57 (9) 7-7 2018年7月

    DOI: 10.7567/jjap.57.0902bc  

  41. Strategy to utilize transmission electron microscopy and X-ray diffraction to investigate biaxial strain effect in epitaxial BiFeO3 films 招待有り 査読有り

    Bae, I. T., Ichinose, T., Yasui, S., Kovacs, A., Zhao, H. J., Iniguez, J., Naganuma, H.

    Japanese Journal of Applied Physics 57 (9) 12-12 2018年6月

    DOI: 10.7567/jjap.57.0902a5  

  42. 化学溶液堆積法を用いたビスマスフェライト/コバルトフェライト二層膜の作製 招待有り 査読有り

    永沼 博, 曽根 圭太, 岡村 総一郎

    まぐね 13 (2) 82-88 2018年4月

  43. Growth and electrostatic/chemical properties of Metal/LaAlO3/SrTiO3 heterostructures 査読有り

    Diogo Castro Vaz, Edouard Lesne, Anke Sander, Hiroshi Naganuma, Eric Jacquet, Jacobo Santamaria, Agnès Barthélémy, Manuel Bibes

    Journal of Visualized Experiments 2018 (132) 56951-56951 2018年2月8日

    出版者・発行元:Journal of Visualized Experiments

    DOI: 10.3791/56951  

    ISSN:1940-087X

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    The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

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

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

    IEEE Magnetics Letters 9 3102005-1-3102005-5 2018年2月7日

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

    DOI: 10.1109/LMAG.2018.2803737  

    ISSN:1949-307X

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    We investigate the amplification of externally excited spin-waves via the spin-transfer-torque (STT) effect in combination with the spin-Hall effect (SHE) resulting from short current pulses. In the case of overcompensation of the spin-wave damping, a strong nonlinear shift of the spin-wave frequency spectrum occurs. In particular, this shift limits spin-wave amplification from the SHE-STT effect. However, it allows for the realization of a spin-wave switch. At the corresponding working point, efficient spin-wave excitation is possible only in the presence of the SHE-STT effect with a spin-wave intensity that is a factor of 20 larger than in the absence of the SHE-STT effect.

  45. 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) 0224011-0224015 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

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    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.

  46. 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) 1400205-1-1400205-5 2017年9月

    出版者・発行元:None

    DOI: 10.1109/TMAG.2017.2707081  

    ISSN:0018-9464

    eISSN:1941-0069

  47. Noise suppression and sensitivity manipulation of magnetic tunnel junction sensors with soft magnetic Co70.5Fe4.5Si15B10 layer 査読有り

    L. Huang, Z. H. Yuan, B. S. Tao, C. H. Wan, P. Guo, Q. T. Zhang, L. Yin, J. F. Feng, T. Nakano, H. Naganuma, H. F. Liu, Y. Yan, X. F. Han

    JOURNAL OF APPLIED PHYSICS 122 (11) 113903-1-113903-7 2017年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4990478  

    ISSN:0021-8979

    eISSN:1089-7550

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    The voltage noise characteristic and sensitivity of magnetic tunnel junction sensors are crucial for ultralow field detection. In this work, we used a soft magnetic material electrode Co70.5Fe4.5Si15B10 as a sensing layer to improve the sensitivity. Then, a bias field along the easy axis of a free layer was applied to improve the linearity and manipulate the sensitivity of magnetic tunnel junction sensors. More importantly, random telegraph noise was suppressed by the bias field, resulting in hysteresis-free performance. The highest sensitivity of 3.9%/Oe and the best field detectivity of 4.5nT/ root Hz at 10 Hz without hysteresis have been achieved. The sensors showed excellent performance with CoFeSiB electrodes, indicating that it is an effective way to improve the performance of sensors by introducing the bias field. Published by AIP Publishing.

  48. Tuning Up or Down the Critical Thickness in LaAlO3/SrTiO3 through In Situ Deposition of Metal Overlayers 査読有り

    Diogo Castro Vaz, Edouard Lesne, Anke Sander, Hiroshi Naganuma, Eric Jacquet, Jacobo Santamaria, Agnes Barthelemy, Manuel Bibes

    ADVANCED MATERIALS 29 (28) 17486-1-17486-8 2017年7月

    出版者・発行元:WILEY-V C H VERLAG GMBH

    DOI: 10.1002/adma.201700486  

    ISSN:0935-9648

    eISSN:1521-4095

    詳細を見る 詳細を閉じる

    The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 and SrTiO3 has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LaAlO3 thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. In this paper, the chemical, electronic, and transport properties of LaAlO3/SrTiO3 samples capped with different metals grown in a system combining pulsed laser deposition, sputtering, and in situ X-ray photoemission spectroscopy are investigated. The results show that for metals with low work function a q2DES forms at 1-2 uc of LaAlO3 and is accompanied by a partial oxidation of the metal, a phenomenon that affects the q2DES properties and triggers the formation of defects. In contrast, for noble metals, the critical thickness is increased above 4 uc. The results are discussed in terms of a hybrid mechanism that incorporates electrostatic and chemical effects.

  49. Elucidation of crystal and electronic structures within highly strained BiFeO3 by transmission electron microscopy and first-principles simulation 査読有り

    In-Tae Bae, Andras Kovacs, Hong Jian Zhao, Jorge Iniguez, Shintaro Yasui, Tomohiro Ichinose, Hiroshi Naganuma

    SCIENTIFIC REPORTS 7 46498-1-46498-11 2017年4月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/srep46498  

    ISSN:2045-2322

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    Crystal and electronic structures of similar to 380 nm BiFeO3 film grown on LaAlO3 substrate are comprehensively studied using advanced transmission electron microscopy (TEM) technique combined with first-principles theory. Cross-sectional TEM images reveal the BiFeO3 film consists of two zones with different crystal structures. While zone II turns out to have rhombohedral BiFeO3, the crystal structure of zone I matches none of BiFeO3 phases reported experimentally or predicted theoretically. Detailed electron diffraction analysis combined with first-principles calculation allows us to determine that zone I displays an orthorhombic-like monoclinic structure with space group of Cm (=8). The growth mechanism and electronic structure in zone I are further discussed in comparison with those of zone II. This study is the first to provide an experimentally validated complete crystallographic detail of a highly strained BiFeO3 that includes the lattice parameter as well as the basis atom locations in the unit cell.

  50. 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 3108005-1-3108005-5 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.

  51. Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces 査読有り

    E. Lesne, Yu Fu, S. Oyarzun, J. C. Rojas-Sanchez, D. C. Vaz, H. Naganuma, G. Sicoli, J. -P. Attane, M. Jamet, E. Jacquet, J. -M. George, A. Barthelemy, H. Jaffres, A. Fert, M. Bibes, L. Vila

    NATURE MATERIALS 15 (12) 1261-1266 2016年12月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/NMAT4726  

    ISSN:1476-1122

    eISSN:1476-4660

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    The spin-orbit interaction couples the electrons' motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism the Rashba effect in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.

  52. 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) 174425-1-174425-11 2016年11月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.94.174425  

    ISSN:2469-9950

    eISSN:2469-9969

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    We have systematically investigated the Gilbert damping constant a for L1(0)-FePd films using the time-resolved magneto-optical Kerr effect (TRMOKE). The field angle dependence of TRMOKE signals was measured and analyzed. The field angle dependence of the lifetime of magnetization precession was explained by evaluating extrinsic contributions such as the anisotropy distribution and two-magnon scattering. The crystalline uniaxial perpendicular magnetic anisotropy constant K-u and alpha values were evaluated for FePd films for various L1(0) order parameters S. K-u values of approximately 15 Merg/cm(3) were obtained for films with large-S values (i.e., over 0.8). In addition, alpha for the low-S film was found to be approximately 0.007 and decreased with increasing S. Smaller values of alpha (of 0.002-0.004) were obtained for films with S values of approximately 0.6-0.8. Results revealed that FePd films have both large-K-u and small-alpha values, which is a useful property for low-power magnetization switching while maintaining high thermal stability in spin-transfer-torque magnetoresistive random access memory applications.

  53. Field-free spin Hall effect driven magnetization switching in Pd/Co/IrMn exchange coupling system 査読有り

    W. J. Kong, Y. R. Ji, X. Zhang, H. Wu, Q. T. Zhang, Z. H. Yuan, C. H. Wan, X. F. Han, T. Yu, Kenji Fukuda, Hiroshi Naganuma, Mean-Jue Tung

    APPLIED PHYSICS LETTERS 109 (13) 132402-1-132402-4 2016年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4963235  

    ISSN:0003-6951

    eISSN:1077-3118

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    All electrical manipulation of magnetization is crucial and of great important for spintronics devices for the sake of high speed, reliable operation, and low power consumption. Recently, widespread interests have been aroused to manipulate perpendicular magnetization of a ferromagnetic layer using spin-orbit torque (SOT) without field. We report that a commonly used antiferromagnetic material IrMn can be a promising candidate as a functional layer to realize field-free magnetization switching driven by SOT in which IrMn is employed to act as both the source of effective exchange bias field and SOT source. The critical switching current density within our study is J(c) = 2.2 x 10(7) A/cm(2), which is the samemagnitude as similar materials such as PtMn. A series of measurements based on anomalous Hall effect was systematically implemented to determine the magnetization switching mechanism. This study offers a possible route for IrMn application in similar structures. Published by AIP Publishing.

  54. 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.

  55. 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) 4001304-1-4001304-4 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.

  56. 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) 063003-1-063003-4 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

  57. 三方位からの透過形電子顕微鏡観察と構造因子計算によるBiFeO3エピタキシャル薄膜の結晶対称性の決定 査読有り

    裵 寅兌, 永沼 博

    日本結晶学会誌 58 (2) 96-102 2016年4月30日

    出版者・発行元:日本結晶学会

    DOI: 10.5940/jcrsj.58.96  

    ISSN:0369-4585

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    Despite extensive studies on crystal structure of thin film BiFeO3 (BFO) thin film, it remains debated primarily due to its structural complexity as well as stress effect from underlying substrates. We have examined comprehensive crystal structure analysis for BFO thin layer (30 nm) grown on SrTiO3 (STO) substrate using cross-sectional transmission electron microscopy technique along three different zone axes. Nano-beam electron diffraction (NBED) patterns combined with structure factor (SF) calculations and high-resolution transmission electron microscopy images unambiguously reveal that BFO thin layer grows with rhombohedral structure that is identical to its bulk form. No evidence of monoclinic and/or tetragonal distortion is found. The rhombohedral BFO thin layer is found to grow onto STO by maintaining an epitaxial relationship in a manner that can minimize lattice mismatch at BFO/STO interface. Our current work clearly demonstrates that multiple-zone axes NBED combined with SF calculation is highly effective for precise crystal structure analysis of thin film BFO.

  58. Thickness dependence of crystal and electronic structures within heteroepitaxially grown BiFe O3 thin films 査読有り

    In-Tae Bae, Hiroshi Naganuma, Tomohiro Ichinose, Kazuhisa Sato

    Physical Review B - Condensed Matter and Materials Physics 93 (6) 2016年2月24日

    出版者・発行元:American Physical Society

    DOI: 10.1103/PhysRevB.93.064115  

    ISSN:1550-235X 1098-0121

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    Crystal and electronic structures of BiFeO3 thin films (∼10 and ∼300 nm) grown on SrTiO3 substrate have been investigated in terms of BiFeO3 film thickness dependence using the advanced transmission electron microscopy (TEM) technique. Electron diffraction patterns of both BiFeO3 thin films acquired along [011]SrTiO3 cross sections clearly exhibited the existence of extra Bragg's reflections which are absent in that from SrTiO3. Structure factor calculations unambiguously revealed that the electron diffraction pattern corresponds to the [211] net pattern of rhombohedral BiFeO3. High-resolution TEM images combined with multislice simulation also demonstrated that the crystalline structure of both BiFeO3 films is rhombohedral. Electron energy loss spectroscopy results for both BiFeO3 thin films showed spectra with the characteristics of bulk BiFeO3, i.e., rhombohedral. The lattice mismatch of &lt 2.5% between BiFeO3 and SrTiO3 found in a particular epitaxial relationship is considered to be the reason that BiFeO3 can grow by maintaining its bulk crystalline, i.e., rhombohedral, structure.

  59. 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.

  60. Thickness dependence of crystal and electronic structures within heteroepitaxially grown BiFeO3 thin films 査読有り

    In-Tae Bae, Hiroshi Naganuma, Tomohiro Ichinose, Kazuhisa Sato

    PHYSICAL REVIEW B 93 (6) 064115-1-064115-6 2016年2月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.93.064115  

    ISSN:2469-9950

    eISSN:2469-9969

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    Crystal and electronic structures of BiFeO3 thin films (similar to 10 and similar to 300 nm) grown on SrTiO3 substrate have been investigated in terms of BiFeO3 film thickness dependence using the advanced transmission electron microscopy (TEM) technique. Electron diffraction patterns of both BiFeO3 thin films acquired along [011](SrTiO3) cross sections clearly exhibited the existence of extra Bragg's reflections which are absent in that from SrTiO3. Structure factor calculations unambiguously revealed that the electron diffraction pattern corresponds to the [211] net pattern of rhombohedral BiFeO3. High-resolution TEM images combined with multislice simulation also demonstrated that the crystalline structure of both BiFeO3 films is rhombohedral. Electron energy loss spectroscopy results for both BiFeO3 thin films showed spectra with the characteristics of bulk BiFeO3, i.e., rhombohedral. The lattice mismatch of <2.5% between BiFeO3 and SrTiO3 found in a particular epitaxial relationship is considered to be the reason that BiFeO3 can grow by maintaining its bulk crystalline, i.e., rhombohedral, structure.

  61. Magnetic properties of weak itinerant ferromagnetic ζ-Fe <sub>2</sub> N film

    Hiroshi Naganuma

    Science and Technology of Advanced Materials 2016年

    DOI: 10.1016/J.STAM.2003.10.008  

  62. 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.

  63. Low frequency noise in magnetic tunneling junctions with Co40Fe40B20/Co70.5Fe4.5Si15B10 composite free layer 査読有り

    Z. H. Yuan, J. F. Feng, Peng Guo, C. H. Wan, H. X. Wei, S. S. Ali, X. F. Han, T. Nakano, H. Naganuma, Y. Ando

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 398 215-219 2016年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2015.09.026  

    ISSN:0304-8853

    eISSN:1873-4766

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    Magnetic tunneling junctions with Co40Fe40B20/Co70.5Fe4.5Si15B10 composite free layer have been fabricated and annealed at different temperatures to obtain the highest tunneling magnetoresistance. The field and temperature dependences of the low frequency noise have been measured to understand the origin of noise. The random telegraph noise has been observed at low magnetic field, and the corresponding fluctuating moment is estimated to be 4.8 x 10(5) mu(B) with an effective area of 240 nm(2). The dependence of noise on temperature was coincident with the thermally activated kinetics model above 30 K while it deviated from this model below 30 K. Studying the origin of the low frequency noise is helpful to reduce the noise level in MTJs. (C) 2015 Elsevier B.V. All rights reserved.

  64. 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) 035002-1-035002-7 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.

  65. 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) 4005104-1-4005104-4 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.

  66. Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers 査読有り

    Z. H. Yuan, L. Huang, J. F. Feng, Z. C. Wen, D. L. Li, X. F. Han, Takafumi Nakano, T. Yu, Hiroshi Naganuma

    JOURNAL OF APPLIED PHYSICS 118 (5) 053904-1-053904-4 2015年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4927840  

    ISSN:0021-8979

    eISSN:1089-7550

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    MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir22Mn78 (6)/Ni80Fe20 (t(NiFe) = 20-70)/Ru (0.9)/Co40Fe40B20 (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 degrees C. Combining the spin-valve-like sensing structure and a soft magnetic NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications. (C) 2015 AIP Publishing LLC.

  67. Influence of perpendicular magnetic field on angular dependent exchange bias of [Co/Pd]&lt;inf&gt;5&lt;/inf&gt;/CoFeB Electrodes 査読有り

    Q. Zhang, T. Yu, H. Naganuma, D. Shi, X. Han

    2015 IEEE International Magnetics Conference, INTERMAG 2015 2015年7月14日

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

    DOI: 10.1109/INTMAG.2015.7156581  

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    In perpendicular magnetic anisotropy (PMA) multilayers electrode system, the low spin polarization and large lattice mismatch between traditional PMA electrodes ([Co/Pt]&lt inf&gt n&lt /inf&gt , [Co/Pd]&lt inf&gt n&lt /inf&gt ) and spin-filter barrier MgO make it difficult to obtain large tunneling magneto-resistance (TMR) ratio [1]. One of several possible solutions is to insert a magnetic electrode between MgO barrier and PMA multilayers electrodes, forming composite magnetic electrodes [2]. Therefore, it is critical to understand magnetic behavior of composite magnetic electrodes. Cain et al early found exchange bias like effect in NiFe/TbCo (FM-FM) bilayers [3]. They explained that tilt of spins at the interface between TbCo and NiFe is responsible for the observed exchange bias like effect. Recently, by applying a large in-plane magnetic field, B. Dieny et al initialized exchange bias in NiFe/[Pt/Co] (FM-FM) bilayer [4] and explained exchange bias like effect using closure domain model [5, 6]. People believe that closure domain formed at the interface is responsible for observed exchange bias. But few works were studied to figure out how perpendicular magnetic field affect closure domain and exchange bias like effect.

  68. 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) 164016-1-164016-7 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.

  69. 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) 164012-1-164012-7 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.

  70. 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) 164015-1-164015-7 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.

  71. 100-nm-sized magnetic domain reversal by the magneto-electric effect in self-assembled BiFeO3/CoFe2O4 bilayer films 査読有り

    Keita Sone, Hiroshi Naganuma, Masaki Ito, Takamichi Miyazaki, Takashi Nakajima, Soichiro Okamura

    SCIENTIFIC REPORTS 5 9348-1-9348-8 2015年4月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/srep09348  

    ISSN:2045-2322

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    A (001)-epitaxial-BiFeO3/CoFe2O4 bilayer was grown by self-assembly on SrTiO3 (100) substrates by just coating a mixture precursor solution. The thickness ratio of the bilayer could be controlled by adjusting the composition ratio. For example, a BiFeOx : CoFe2Ox = 4 : 1 (namely Bi4CoFe6Ox) mixture solution could make a total thickness of 110 nm divided into 85-nm-thick BiFeO3 and 25-nm-thick CoFe2O4. Self-assembly of the bilayer occurred because the perovskite BiFeO3 better matched the lattice constant (misfit approximately 1%) and crystal symmetry of the perovskite SrTiO3 than the spinel CoFe2O4 (misfit approximately 7%). The magnetic domains of the hard magnet CoFe2O4 were switched by the polarization change of BiFeO3 due to an applied vertical voltage, and the switched magnetic domain size was approximately 100 nm in diameter. These results suggest that self-assembled BiFeO3/CoFe2O4 bilayers are interesting in voltage driven nonvolatile memory with a low manufacturing cost.

  72. Evidence of rhombohedral structure within BiFeO3 thin film grown on SrTiO3 査読有り

    In-Tae Bae, Hiroshi Naganuma

    APPLIED PHYSICS EXPRESS 8 (3) 031501-1-031501-4 2015年3月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.8.031501  

    ISSN:1882-0778

    eISSN:1882-0786

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    Comprehensive crystal structure analysis was performed for a BiFeO3 thin layer (similar to 30 nm) grown on a SrTiO3 substrate using cross-sectional transmission electron microscopy along three different zone axes. Nano-beam electron diffraction patterns combined with structure factor calculations and high-resolution transmission electron microscopy images unambiguously revealed that the BiFeO3 thin layer grew with a rhombohedral structure identical to its bulk form. No evidence of monoclinic and/or tetragonal distortion was found. The rhombohedral BiFeO3 thin layer was found to grow onto SrTiO3 by maintaining an epitaxial relationship in a manner minimizing the lattice mismatch at the BiFeO3/SrTiO3 interface. (C) 2015 The Japan Society of Applied Physics

  73. 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 8537-1-8537-6 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.

  74. 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).

  75. 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.

  76. 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

    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.

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

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

    Journal of Applied Physics 117 (17) 17D140-1-17D140-3 2015年1月

    DOI: 10.1063/1.4917334  

  78. S. Iihama, M Khan, H. Naganuma, M. Oogane, S. Mizukami, Y. Ando 査読有り

    永沼 博

    Journal of Magnetic Scoiety of Japan 39 57-61 2015年1月

  79. Preparationofmonoclinic0.9(BiFeO3)–0.1(BiCoO3) epitaxial films on orthorhombicYAlO3 (100)substratesbyr.f.magnetronsputtering 査読有り

    Tomohiro Ichinose, Hiroshi Naganuma, Koki Mukaiyama, Mikihiko Oogane, Yasuo Ando

    Journal of Crystal Growth 409 18-22 2015年1月

    出版者・発行元:None

    DOI: 10.1016/j.jcrysgro.2014.09.044  

    ISSN:0022-0248

    eISSN:1873-5002

  80. 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 3700104-1-3700104-4 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.

  81. Electrical Detection of Millimeter-Waves by Magnetic Tunnel Junctions Using Perpendicular Magnetized L10‑FePd Free Layer 査読有り

    Hiroshi Naganuma, G. Kim, 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:None

    DOI: 10.1021/nl504114v  

    ISSN:1530-6984

    eISSN:1530-6992

  82. 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.

  83. 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) 227601-1-227601-5 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.

  84. 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) 142403-1-142403-4 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.

  85. 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

    詳細を見る 詳細を閉じる

    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.

  86. Fabrication of integrated magnetic tunnel junctions for detection of bio-magnetic field 査読有り

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

    Transactions of Japanese Society for Medical and Biological Engineering 52 O-505-0-506 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.O-505  

    ISSN:1347-443X 1881-4379

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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/f noise, 100×100 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 100×100 MTJ sensor array.

  87. 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) 052407-1-052407-4 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.

  88. 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) 087133-1-087133-10 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).

  89. Multiferroic BiFeO3 glass-ceramics: Phase formation and physical property 査読有り

    Yoshihiro Takahashi, Kousuke Meguro, Hiroshi Naganuma, Nobuaki Terakado, Takumi Fujiwara

    APPLIED PHYSICS LETTERS 104 (22) 221901-1-221901-3 2014年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4881138  

    ISSN:0003-6951

    eISSN:1077-3118

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    A production of polycrystalline phase with glassy precursor, i.e., glass-ceramics processing, has a great potential to fabricate the sophisticated materials. In this study, we have prepared the Bi2O3-Fe2O3-BaO-B2O3 system precursor, in which BiFeO3 phase is crystallizable, and examined the phase formation and physical properties in resulting glass-ceramics. We found both ferroelectricity and ferromagnetism in the glass-ceramics consisting of BiFeO3 phase, i.e., multiferroic glass-ceramics. This study has demonstrated an alternative method for synthesis of polycrystalline BiFeO3 material. (C) 2014 AIP Publishing LLC.

  90. 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 063068-1-063068-17 2014年6月

    出版者・発行元:IOP PUBLISHING LTD

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

    ISSN:1367-2630

    詳細を見る 詳細を閉じる

    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.

  91. 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) 17D133-1-17D133-3 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.

  92. Leakage current under high electric fields and magnetic properties in Co and Mn co-substituted BiFeO3 polycrystalline films 査読有り

    Jun Miura, Takashi Nakajima, Hiroshi Naganuma, Soichiro Okamura

    THIN SOLID FILMS 558 194-199 2014年5月

    出版者・発行元:ELSEVIER SCIENCE SA

    DOI: 10.1016/j.tsf.2014.03.046  

    ISSN:0040-6090

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    Co and Mn co-substituted BiFeO3 films were prepared on Pt/Ti/SiO2/Si(100) substrates, and the effect of co-substitution on the structural, electric, and magnetic properties of the prepared films was systematically investigated. Cross-sectional transmission electron microscopy observations showed that the films were homogeneous; moreover, no magnetic secondary phases were observed in the films. Nano-beam energy-dispersive X-ray spectroscopy, carried out at various points in the films, revealed that Co and Mn were distributed in the films. Further, the average concentration of Bi, Co, Mn, and Fe was 59, 2, 2, and 37 at.%, respectively; these values were almost consistent with the nominal composition of the precursor solution used. X-ray diffraction profiles of the films showed that the (012)-d-spacing decreased and (104) and (110) peaks merged into a single peak with increasing co-substitution content. The leakage current in films under high electric fields drastically decreased upon co-substitution without any degradation of ferroelectricity; moreover, this effect was also observed for single Mn-substituted materials. Saturation magnetization of the films monotonically increased with the co-substitution content, and this increase was quantitatively identical to that in the case of single Co-substituted materials. These results indicate that Co and Mn play significant roles in determining the properties of co-substituted BiFeO3 films. (C) 2014 Published by Elsevier B.V.

  93. Spin-dependent transport behavior in C-60 and Alq(3) based spin valves with a magnetite electrode (invited) 招待有り 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) 172608-1-172608-6 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.

  94. 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) 174416-1-174416-6 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.

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

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

    Journal of Applied Physics 115 (17) 17C704-1-17C704-3 2014年1月6日

    DOI: 10.1063/1.4855016  

  96. 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.

  97. 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.

  98. 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

  99. 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) 103004-1-103004-3 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

  100. 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) 163904-1-163904-10 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.

  101. 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) 163913-1-163913-3 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.

  102. 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.

  103. 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) 073002-1-073002-4 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

  104. 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) 063003-1-063003-4 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

  105. Large refractive index in BiFeO3-BiCoO3 epitaxial films 査読有り

    Hiromi Shima, Ken Nishida, Takashi Yamamoto, Toshiyasu Tadokoro, Koichi Tsutsumi, Michio Suzuki, Hiroshi Naganuma

    JOURNAL OF APPLIED PHYSICS 113 (17) 17A914-1-17A914-3 2013年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4794878  

    ISSN:0021-8979

    eISSN:1089-7550

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    Rhombohedral (R-) and tetragonal (T-) Bi(Fe, Co)O-3 (BFCO) films were epitaxially grown on the SrTiO3 (100) substrates, and the optical properties of the BFCO films were evaluated by spectroscopic ellipsometry. It was revealed that the refractive indexes of R- and T-BFCO epitaxial films were 2.93 and 2.86 at wavelength of 600 nm, and 2.65 and 2.59 at 1550 nm, respectively, which are comparable to the pure BiFeO3. The refractive index of the R-BFCO film was totally larger than that of the T-BFCO film; it might be caused by structural strain and local symmetry breaking. It was confirmed that the extinction coefficients of both films were almost zero at wavelengths larger than 600 nm. In addition, the optical band gaps of the R- and T-BFCO films were estimated to be 2.78 and 2.75 eV, respectively. It can expect that the BFCO film has a possibility to use optical-magnetic field sensor working at room temperature. (C) 2013 American Institute of Physics.

  106. 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) 184426-1-184426-8 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.

  107. 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) 155001-1-155001-7 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.

  108. 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) 04CM07-1-04CM07-3 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.

  109. Structural and magnetic properties of L10-FePd/MgO films on GaAs and InP lattice mismatched substrates 査読有り

    M. Kohda, S. Iimori, R. Ohsugi, H. Naganuma, T. Miyazaki, Y. Ando, J. Nitta

    Applied Physics Letters 102 (10) 102411-1-102411-3 2013年3月11日

    DOI: 10.1063/1.4795443  

    ISSN:0003-6951

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    Structural and magnetic properties of epitaxial L10-FePd/MgO films on GaAs and InP lattice mismatched substrates are investigated at different MgO and FePd growth temperatures. While c-axis lattice constants of MgO and FePd show similar values on both substrates, the remanent magnetization becomes larger on GaAs than that on InP. Since the ratio of FePd (002) tetragonal ordered phase and FePd (200) cubic disordered phase follows similar growth temperature dependence to the remanent magnetization and the long range chemical order parameter, the perpendicular magnetic anisotropy grown on the lattice-mismatched semiconductors is strongly affected by formation of the disordered phase. © 2013 American Institute of Physics.

  110. 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) 067201-1-067201-4 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

  111. 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.

  112. 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 1392-1399 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.

  113. 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.

  114. Annealing Temperature and Co Layer Thickness Dependence of Magnetoresistance Effect for L1(0)-MnGa/Co/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions 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 48 (11) 2808-2811 2012年11月

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

    DOI: 10.1109/TMAG.2012.2196420  

    ISSN:0018-9464

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    The post annealing temperature and Co thickness dependence of tunnel magnetoresistance (TMR) ratio was investigated for L1(0)-MnGa/Co(t(Co))/MgO/CoFeB perpendicular magnetic tunnel junctions (MTJs). The MnGa/MgO interface optimization by Co insertion was shown to be an effective way for improving the TMR ratio. The TMR value increases with the annealing temperature, (T-a), and exhibits maxima at 325 degrees C for t(Co) = 1.0 - 5.0 nm. Thermal annealing process improves the structure of MTJs, but also causes elements diffusion. In this work, the annealing effect on MTJs with different Co thicknesses was discussed in detail along with a fast annealing method.

  115. Magnetic Properties and Magnetic Domain Structures Evolution Modulated by CoFeB Layer in [Pd/Co]/CoFeB/MgO/CoFeB/[Co/Pd] Perpendicular MTJ Films 査読有り

    T. Yu, H. Naganuma, D. W. Shi, Y. Ando, X. F. Han

    IEEE TRANSACTIONS ON MAGNETICS 48 (11) 2812-2815 2012年11月

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

    DOI: 10.1109/TMAG.2012.2198795  

    ISSN:0018-9464

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    A series of MgO perpendicular magnetic tunneling junction (p-MTJ) films with soft/hard composite electrodes is prepared by RF-sputtering, where amorphous CoFeB is chosen as soft layer. The modulation of MTJs film magnetic properties on CoFeB thickness is investigated. The critical thickness for composite free layer transform from rigid magnet (RM) to exchange spring system (ES) is indentified. Besides, an unexpected in-plane exchange bias is observed which is attributed to the formation of closure domains. The evolution of domain structures on CoFeB is examined by magnetic force microscope. Coexistence of two distinguished magnetic domains of different sizes is observed. It is found that the evolution of domain morphology as varying CoFeB thickness is due to the modulation of effective anisotropy.

  116. 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) 072901-1-072901-3 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]

  117. Chemical diffusion: Another factor affecting the magnetoresistance ratio in Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junction 査読有り

    Y. Yang, W. X. Wang, Y. Yao, H. F. Liu, H. Naganuma, T. S. Sakul, X. F. Han, R. C. Yu

    APPLIED PHYSICS LETTERS 101 (1) 012406-1-012406-3 2012年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4732463  

    ISSN:0003-6951

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    This letter investigates the microstructure and mean inner potential (MIP) profile of Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junctions (MTJs) by high resolution transmission electron microscopy (HRTEM) and electron holography, respectively. The inconspicuous crystallization of MgO barrier is confirmed by HRTEM in the post-annealed sample at 250 degrees C. An obvious MIP difference is displayed in the Ta layers between the top and bottom of the MTJ, and elemental content difference of them is confirmed by energy dispersive spectroscopy. These results imply that the chemical diffusion can also give rise to a lower tunnel magnetoresistance ratio besides the inconspicuous crystallization of MgO barrier. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732463]

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

    Hiroshi Naganuma

    Applied Physics Letters 101 (3) 032402-1-032402-3 2012年6月16日

    DOI: 10.1063/1.4737000  

  119. Structural Analyses of Co- and Mn-Substituted BiFeO3 Polycrystalline Films 査読有り

    Hiroshi Naganuma, Keita Sone, In-Tae Bae, Takamichi Miyazaki, Jun Miura, Takashi Nakajima, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 51 (6) 061501-1-061501-3 2012年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.51.061501  

    ISSN:0021-4922

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    Mn- and Co-BiFeO3 polycrystalline films were prepared by a chemical solution deposition (CSD) method and their structures were investigated by grazing incidence X-ray diffraction (GIXRD) and theta-2 theta XRD in conjunction with transmission electron microscopy (TEM). GIXRD measurement revealed that the Mn-BiFeO3 film contains the Bi2Fe4O9 pyrochlore phase, which might be attributed to the low magnetization of the Mn-BiFeO3 film. For the Co-BiFeO3 film, secondary phases were not observed by structural analyses and the composition was almost homogeneous. From the analytic aspect of the structure, the magnetization enhancement in the Co-BiFeO3 films is considered to be associated with Co substitution for Fe in BiFeO3. (c) 2012 The Japan Society of Applied Physics

  120. Magnetic properties of CoFe2O4 nanoparticles distributed in a multiferroic BiFeO3 matrix 査読有り

    Keita Sone, Sho Sekiguchi, Hiroshi Naganuma, Takamichi Miyazaki, Takashi Nakajima, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 111 (12) 124101-1-124101-5 2012年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4729831  

    ISSN:0021-8979

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    BiFeO3-CoFe2O4 composite thin films were formed on Pt/Ti/SiO2/Si(100) substrates by chemical solution deposition from a mixed precursor solution. X-ray diffraction and transmission electron microscopy analyses confirmed that CoFe2O4 nanoparticles less than 10 nm were uniformly distributed in the BiFeO3 matrix. The BiFeO3-CoFe2O4 composite films exhibited the same ferroelectric switching charge as BiFeO3 thin films, although a larger applied electric field was necessary. However, the magnetic properties were significantly improved by incorporation of CoFe2O4 nanoparticles into BiFeO3; a saturated magnetization of 80 emu/cm(3) and a magnetic coercive field of 450 Oe were attained at 300 K. Furthermore, the composite films did not show superparamagnetic behavior in zero-field-cooling and field-cooling measurements, which suggest that the thermal fluctuation of CoFe2O4 nanoparticles was suppressed by exchange coupling with BiFeO3. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729831]

  121. Variation of ferroelectric properties in (Bi,Pr)(Fe,Mn)O-3/SrRuO3-Pt/CoFe2O4 layered film structure by applying direct current magnetic field 査読有り

    Chen Liu, Takeshi Kawae, Yoshinori Tsukada, Akiharu Morimoto, Hiroshi Naganuma, Takashi Nakajima, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 111 (12) 124103-1-124103-5 2012年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4730334  

    ISSN:0021-8979

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    We report the preparation of (Bi,Pr)(Fe,Mn)O-3(BPFM)/SrRuO3 (SRO)-Pt/CoFe2O4(CFO) layered film structure on (100) SrTiO3 substrate by pulsed laser deposition method and their structural and electrical properties. Favorable ferroelectric properties of BPFM were observed in the layered film structure with (100)-oriented growth of BPFM, SRO, and CFO. Variation of polarization vs electric field loops of BPFM by applying DC magnet field was observed, and the remnant polarization was found to increase by 3% with increasing the applied magnetic field from 0 to 10 kOe. The magnetoelectric coefficient in the present structure was estimated to be 1.5 V/(cmOe). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730334]

  122. 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) 043003-1-043003-3 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

  123. 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) 07A324-1-07A324-3 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]

  124. 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) 07C905-1-07C905-3 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]

  125. 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) 07C112-1-07C112-3 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]

  126. Annealing temperature dependence of exchange bias in BiFeO3/CoFe bilayers 査読有り

    T. Yu, H. Naganuma, W. X. Wang, Y. Ando, X. F. Han

    JOURNAL OF APPLIED PHYSICS 111 (7) 07D908-1-07D908-3 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3673435  

    ISSN:0021-8979

    eISSN:1089-7550

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    BiFeO3/CoFe bilayers with different BiFeO3 (BFO) crystalities were fabricated by chemical solution deposition and sputtering method. Exchange bias has been successfully induced in these bilayers by post-annealing. The annealing temperature dependence of exchange bias as well as coercivity was investigated. Two kinds of annealing temperature dependence behaviors were observed. It is found that, similar to the conventional antiferromagnet/ferromagnet system, the temperature dependence of exchange bias is dominated by direct interface coupling, and the crystality of BFO has no profound effect on exchange bias. (C) 2012 American Institute of Physics. [doi:10.1063/1.3673435]

  127. 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) 07B320-1-07B320-3 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]

  128. 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) 07C710-1-07C710-3 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]

  129. 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) 112402-1-112402-3 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]

  130. Electronic Structure of BiFe1-xMx03 (M=Mn and Co) Thin Films by Soft-X-Ray Spectroscopy 査読有り

    Tohru Higuchi, Hiroshi Naganuma, Jun Miura, Yosuke Inoue, Yi-Sheng Liu, Per-Anders Glans, Jinghua Guo, Soichiro Okamura

    Trans. mater. Res. Soc. Jpn 37 (1) 77-80 2012年1月1日

    出版者・発行元:The Materials Research Society of Japan

    DOI: 10.14723/tmrsj.37.77  

    ISSN:1382-3469

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    The electronic structures of BiFe<sub>0.96</sub>Mn<sub>0.04</sub>O<sub>3</sub> and BiFe<sub>0.96</sub>Co<sub>0.04</sub>O<sub>3</sub> thin films have studied by X-ray absorption spectroscopy and soft-X-ray emission spectroscopy. The BiFe<sub>0.96</sub>Mn<sub>0.04</sub>O<sub>3</sub> thin film has the mixed valence states of Mn<sup>3+</sup> and Mn<sup>4+</sup>, although the BiFe<sub>0.96</sub>Co<sub>0.04</sub>O<sub>3</sub> thin film has the valence state of Co<sup>3+</sup>. The conduction band consists of the Fe 3<i>d</i> state. The valence band is mainly composed of the O 2<i>p</i> state hybridized with the Fe 3<i>d</i> state. The bandwidth of valence band depends on the valence state of doped element. The energy gap of BiFe<sub>0.96</sub>Mn<sub>0.04</sub>O<sub>3</sub> thin film is smaller than that of BiFe<sub>0.96</sub>Co<sub>0.04</sub>O<sub>3</sub> thin film. These findings may indicate that the leakage current of thin film is closely related with the electronic structure and energy gap.

  131. 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) 014416-1-014416-6 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.

  132. 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) 113005-1-113005-3 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

  133. 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) 192509-1-192509-3 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]

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

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

    IEEE TRANSACTIONS ON MAGNETICS 47 (10) 3897-3900 2011年10月

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

    DOI: 10.1109/TMAG.2011.2154357  

    ISSN:0018-9464

    eISSN:1941-0069

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    Fast precessional dynamics of magnetization are reported in very thin films of CoCrPt alloy with large perpendicular magnetic anisotropy. The films are fabricated with different substrate temperatures, and magnetization dynamics are investigated using time-resolved magneto-optical Kerr effect. The Kittel's equation well describes a dependency of magnetization precession frequency on an applied magnetic field direction for all the films, only when the field is relatively large. An inverse lifetime of magnetization precession, a counterpart of a line width in ferromagnetic resonance (FMR), depends strongly on the field direction even at the applied field of around 10 kOe. The Gilbert damping constant alpha is estimated to be similar to 0.05 for all the films using a model taking account of an influence of perpendicular magnetic anisotropy dispersion.

  135. 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) 162509-1-162509-3 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]

  136. 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) 103003-1-103003-5 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

  137. Spin Transport in Co/Al2O3/Alq(3)/Co Organic Spin Valve 査読有り

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

    Ieee Transactions on Magnetics 47 (10) 2649-2651 2011年9月

    DOI: 10.1109/tmag.2011.2143392  

  138. Hysteresis loops of polarization and magnetization in (BiNd0.05)(Fe0.97Mn0.03)O-3/Pt/CoFe2O4 layered epitaxial thin film grown by pulsed laser deposition 査読有り

    Takeshi Kawae, Jie Hu, Hiroshi Naganuma, Takeshi Nakajima, Yuki Terauchi, Soichiro Okamura, Akiharu Morimoto

    THIN SOLID FILMS 519 (22) 7727-7730 2011年9月

    出版者・発行元:ELSEVIER SCIENCE SA

    DOI: 10.1016/j.tsf.2011.05.067  

    ISSN:0040-6090

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    (BiNd0.05)(Fe0.97Mn0.03)O-3 (BNFM)/Pt/CoFe2O4 (CFO) layered thin film was fabricated on (100) SrTiO3 substrate by pulsed laser deposition. BNFM. Pt, and CFO layers were epitaxially grown on the substrate. Almost no increase of leakage current due to the formation of heteroepitaxial structure was found, and well-saturated hysteresis loops in the polarization vs electric field and magnetization vs magnetic field curves coexist at room temperature. The remnant polarization and remnant magnetization values were 55 mu C/cm(2), and 70-145 mA/m, respectively. (C) 2011 Elsevier B.V. All rights reserved.

  139. Thermooptic Property of Polycrystalline BiFeO3 Film 査読有り

    Hiromi Shima, Koichi Tsutsumi, Michio Suzuki, Toshiyasu Tadokoro, Hiroshi Naganuma, Takashi Iijima, Ken Nishida, Takashi Yamamoto, Takashi Nakajima, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 50 (9) 09NB02-1-09NB02-4 2011年9月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.50.09NB02  

    ISSN:0021-4922

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    We have fabricated a polycrystalline BiFeO3 (BFO) film with a thickness of 650 nm on a Pt/Ti/SiO2/Si substrate by a chemical solution deposition method, and its optical and thermooptic properties were evaluated by spectroscopic ellipsometry. The optical band gap energy of the BFO film was 2.95 eV at 50 degrees C and monotonically decreased with increasing temperature to 2.79 eV at 530 degrees C. The extinction coefficient was significantly low at a wavelength longer than 600 nm in the temperature range from 50 to 530 degrees C. The refractive index of the BFO film was estimated to be 2.96 at 600 nm and 2.68 at 1550 nm at 50 degrees C using a single Gaussian oscillator, and a thermooptic coefficient of 0.8 x 10(-4) K-1 was obtained at a wavelength of 1550 nm. Although the refractive index decreased with increasing temperature at all wavelengths, the variation was larger at shorter wavelengths. This seems to be caused by the combination of broadening in the Gaussian oscillator vibration and thermal expansion. (C) 2011 The Japan Society of Applied Physics

  140. 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) 132513-1-132513-3 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]

  141. The perpendicular anisotropy of Co40Fe40B20 sandwiched between Ta and MgO layers and its application in CoFeB/MgO/CoFeB tunnel junction 査読有り

    W. X. Wang, Y. Yang, H. Naganuma, Y. Ando, R. C. Yu, X. F. Han

    APPLIED PHYSICS LETTERS 99 (1) 012502-1-012502-3 2011年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3605564  

    ISSN:0003-6951

    eISSN:1077-3118

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    Magnetic anisotropy of Co40Fe40B20 thin films sandwiched between Ta and MgO layers was investigated. Magnetic properties of CoFeB layers deposited on top and bottom of MgO layer are different. The thickness of the CoFeB layer and annealing temperature are the critical parameters to achieve and keep the perpendicular magnetic anisotropy. The phase diagram of perpendicular anisotropic strength of CoFeB layers on annealing temperatures and thicknesses of CoFeB layers is observed. According to phase diagrams, perpendicular CoFeB/MgO/CoFeB tunnel junctions were fabricated, and tunneling magnetoresistance (TMR) ratio was higher than 30% at low temperatures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3605564]

  142. Effect of metallic Mg insertion on the magnetoresistance effect in MgO-based tunnel junctions using D0(22)-Mn3-delta Ga 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

    JOURNAL OF APPLIED PHYSICS 110 (1) 013915-1-013915-2 2011年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3603034  

    ISSN:0021-8979

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    Effects of metallic Mg insertion on tunnel magnetoresistance (TMR) effect were investigated in D0(22)-Mn2.4Ga/Mg/MgO/CoFe magnetic tunnel junctions (MTJs). The thickness of Mg (d(Mg)) was varied from 0 to 1.4 nm. TMR ratio exhibited maximum value of 22% with the d(Mg) = 0.4 nm and a negative value of 14% with the d(Mg) = 1.4 nm at 10 K. The dependence of resistance area products (R x A) on the d(Mg) showed similar trend compared with those of what reported in conventional CoFeB-MgO based MTJs. Bias voltage dependences of differential conductance (dI/dV) and TMR ratio exhibited asymmetry with respect to the zero-bias. The difference of the zero-bias anomaly in the dI/dV spectra was also discussed, and an indication of reducing the inelastic tunneling process was found, implying the improvement of barrier/magnetic-layer interfaces by the Mg insertion. Considering a theoretical work done by Wang et al. [Phys. Rev. B 82, 054405 (2010)], the inversion of the sign and the asymmetric bias voltage dependence of TMR ratio were inferred to be attributed to the minority spin tunneling via a quantum well state in the thin metallic Mg layer between Mn2.4Ga and MgO. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3603034]

  143. 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 (6) 1087-1095 2011年6月

    出版者・発行元:MDPI AG

    DOI: 10.3390/ma4061087  

    ISSN:1996-1944

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    The 10 at.% Co-substituted BiFeO3 films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO3 (100) substrates with epitaxial relationships of [001](001)Co-BiFeO3//[001](001)SrTiO3. In this study, a single phase Co-substituted BiFeO3 epitaxial film was fabricated by r.f. magnetron sputtering. Sputtering conditions such as Ar, O-2 gas pressure, annealing temperature, annealing atmosphere, and sputtering power were systematically changed. It was observed that a low Ar gas pressure and low sputtering power is necessary to suppress the formation of the secondary phases of BiOx. The Co-substituted BiFeO3 films were crystalized with post-annealing at 600 degrees C in air. The process window for single phase films is narrower than that for pure BiFeO3 epitaxial films. By substituting Fe with Co in BiFeO3, the magnetization at room temperature increased to 20 emu/cm(3). This result suggests that Co-substituted BiFeO3 films can be used in spin-filter devices.

  144. 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) 043002-1-043002-3 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

  145. Enhancement of magnetization at morphotropic phase boundary in epitaxial BiCoO3-BiFeO3 solid solution films grown on SrTiO3 (100) substrates 査読有り

    Hiroshi Naganuma, Shintaro Yasui, Ken Nishida, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 109 (7) 07D917-1-07D917-3 2011年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3561776  

    ISSN:0021-8979

    eISSN:1089-7550

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    The xBiCoO(3)-(1-x)BiFeO3 [0 &lt;= x &lt;= 58 at. %] solid solution films were epitaxially grown on SrTiO3 (100) substrates, and the dependence of the magnetic properties on the BiCoO3 concentration was systematically investigated. The remanent magnetization (M-r) and coercive field (H-c) increased with the BiCoO3 in the case of rhombohedral composition (x &lt;= 18 at. %), and it maximally enhanced at morphotropic phase boundary (MPB) (20 &lt;= x &lt;= 25 at. %). The magnetization decreased in the case of a tetragonal structure (30 at. % &lt;= x). The magnetoelectric (ME) effect at room temperature expect to observe for the BiCoO3-BiFeO3 solid solution films in the case of the rhombohedral structure and for MPB. (C) 2011 American Institute of Physics. [doi:10.1063/1.3561776]

  146. 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) 07D736-1-07D736-3 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]

  147. 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) 117201-1-117201-4 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.

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

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 208 (3) 675-678 2011年3月

    出版者・発行元:WILEY-V C H VERLAG GMBH

    DOI: 10.1002/pssa.201026569  

    ISSN:1862-6300

    eISSN:1862-6319

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    The structural and magnetic properties of Co2MnSi films on different oriented n-Ge substrates were compared. The orientation of the substrates changed the growth of the film. Therefore, a significant change of magnetization of Co2MnSi films was noticed depending on the orientation of the Ge substrates. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  149. 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

  150. 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) 013001-1-013001-2 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

  151. Effect of structural transition on the temperature-dependent magnetic properties of epitaxial FePd alloy nanoparticles 査読有り

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010) 266 012042-1-012042-5 2011年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/266/1/012042  

    ISSN:1742-6588

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    We have studied atomic ordering and magnetic properties of epitaxial FePd nanoparticles 3-14 nm in diameter. Thermal fluctuation of magnetic moment of L1(0)-FePd nanoparticles becomes prominent when particle size is smaller than about 8 nm. Atomic images of high-resolution transmission electron microscopy revealed the formation of the ordered phase in FePd nanoparticles as small as 4 nm in diameter, while the superlattice reflections were quite weak compared to those of the larger sized particles (>8nm). The experimental results indicate that the degradation of magnetic anisotropy is induced by the size-dependent decay of long-range atomic order.

  152. 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

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010) 266 012104-1-012104-4 2011年

    出版者・発行元:IOP PUBLISHING LTD

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

    ISSN:1742-6588

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    We fabricated an epitaxially grown B2-ordered Co2MnAl Heusler alloy film by optimizing fabrication conditions, such as composition of the films and annealing temperature. Tunnel magnetoresistance (TMR) effect was investigated in Co2MnSi/Co2MnAl(0-1.0 nm)/MgO/CoFe magnetic tunnel junctions (MTJs). TMR ratio was enhanced by inserting a thin Co2MnAl layer at the Co2MnSi/MgO interface. The MTJ with Co2MnAl thickness of 0.5 nm exhibited the highest TMR ratio at 310 K and 10 K.

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

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

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010) 266 012096-1-012096-5 2011年

    出版者・発行元:IOP PUBLISHING LTD

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

    ISSN:1742-6588

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    Epitaxially grown semimetallic-Fe2VAl Heusler thin films were fabricated on single crystalline MgO (100) substrate. Crystalline structure, magnetic property, and electrical transport property of the films were investigated. Non-magnetic and bulk-like resistivity was achieved in a B2-ordred Fe2VAl film annealed at 700 degrees C. Curret-perpendicular-to-plane (CPP-) Magnetoresistance effect in Co2MnSi/Fe2VAl/CoFe junctions was also investigated. Maximum value of MR ratio was 1.1% at room temperature, which is an evidence of spin-dependent transport through Fe2VAl Heusler alloy.

  154. 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

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010) 266 012112-1-012112-5 2011年

    出版者・発行元:IOP PUBLISHING LTD

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

    ISSN:1742-6588

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    In this study, influence of composition on structure and magnetic properties of epitaxial Mn-Ga films were investigated. The epitaxial Mn-Ga films with different composition were grown on metal (Pt and Cr) buffered MgO substrates by co-sputtering technique. By use of the Pt buffered MgO substrates, the D0(22) phases can be obtained in the Mn-Ga films with the composition ranging from Mn65Ga35 to Mn75Ga25. The crystalline quality and perpendicular magnetic anisotropic properties of the Mn-Ga films were deteriorated with increase of Mn content. The saturation magnetization decreased with the increase of Mn content, which is consistent with the reported results of bulk alloys.

  155. 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) 052501-1-052501-3 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]

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

    Tatsuya Aoki, Yasuo Ando, Mikihiko Oogane, Hiroshi Naganuma

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010) 266 012086 2011年

    出版者・発行元:IOP PUBLISHING LTD

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

    ISSN:1742-6588

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    In the development of spin-transfer torque (STT)-based magnetic random access memories (spin-RAMs), characterizing the physics in sub-ns STT switching is a crucial issue for designing operation schemes. This paper describes the procedure we used to fabricate MgO-based magnetic tunnel junctions for measuring sub-ns STT switching. We also discuss the sub-ns STT switching properties based on the quasi-static properties.

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

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

    Applied Physics Express 4 (1) 013005-1-013005-3 2011年

    DOI: 10.1143/apex.4.013005  

  158. Erratum: “Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr,Ti)O3 thick epitaxial films” †Appl. Phys. Lett. 97, 11901 (2010) 査読有り

    Mitsumasa Nakajima, Takashi Fujisawa, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Minoru Osada

    APPLIED PHYSICS LETTERS 97 (18) 189901-189901 2010年11月4日

    DOI: 10.1063/1.3512958  

  159. Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr,Ti)O-3 thick epitaxial films 査読有り

    Mitsumasa Nakajima, Takashi Fujisawa, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Minoru Osada

    APPLIED PHYSICS LETTERS 97 (11) 111901-1-111901-3 2010年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3488015  

    ISSN:0003-6951

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    We investigated the polarized Raman spectra of a strain-free, unipolar-axis oriented tetragonal Pb(Zr,Ti)O-3 thick epitaxial film. We evaluated the single crystal-like selection rules of the A(1)- and E-symmetry components, and found an anomalous behavior in the angular dependence of the A(1)(1TO)-mode intensity similar to that observed in high-T-c superconductor single crystals. Raman tensor analyses of the A(1)(1TO) mode revealed complex phases may exist between two independent Raman-tensor components even in the single 180 degrees domain state. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488015]

  160. Structural characterization of epitaxial multiferroic BiFeO3 films grown on SrTiO3 (100) substrates by crystallizing amorphous Bi–Fe–Ox 査読有り

    Hiroshi Naganuma, Takamichi Miyazaki, Akihiko Ukachi, Mikihiko Oogane, Yasuo Ando

    Journal of the Ceramic Society of Japan 118 (1380) 648-651 2010年8月

    出版者・発行元:None

    DOI: 10.2109/jcersj2.118.648  

    ISSN:1882-0743

    eISSN:1348-6535

  161. Evaluation of ferroelectric hysteresis loops of leaky multiferroic BiFeO3 films using a system with a high driving frequency of 100 kHz system 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 (1380) 656-658 2010年8月

    出版者・発行元:CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

    DOI: 10.2109/jcersj2.118.656  

    ISSN:1882-0743

    eISSN:1348-6535

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    A measurement system with a high driving frequency of 100 kHz is effective for measuring the ferroelectricity of leaky ferroelectric materials such as multiferroic BiFeO3 films. A high driving frequency reduces the measurement time, leading to a drastic reduction in the influence of the leakage current density on ferroelectric hysteresis loops. Phase-delay compensation is essential in a system with a driving frequency of 100 kHz; in this study a standard capacitor was used for phase-delay compensation. The value of remanent polarization of a BiFeO3 film measured by the 100-kHz system was confirmed by a positive, up, negative and down measurement. (C) 2010 The Ceramic Society of Japan. All rights reserved.

  162. 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) 252501-1-252501-3 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]

  163. 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.

  164. 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.

  165. 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.

  166. 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.

  167. 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) 09C714-1-09C714-3 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]

  168. 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) 142502-1-142502-3 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.

  169. 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) 142501-1-142501-3 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.

  170. 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) 152502-1-152502-3 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).

  171. 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 査読有り

    井波暢人, 永沼博, 平塚喬士, 金国天, 宮崎孝道, 佐藤和久, 今野豊彦, 大兼幹彦, 安藤康夫

    Journal of Magnetic Socienty of Japan 34 (3) 293-296 2010年3月17日

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.1003R047  

    ISSN:1882-2924

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    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.

  172. 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.

  173. Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr, Ti)O-3 thick epitaxial films (vol 97, 11901, 2010)

    Nakajima, M., Fujisawa, T., Ehara, Y., Yamada, T., Funakubo, H., Naganuma, H., Okamura, S., Nishida, K., Yamamoto, T., Osada, M.

    Applied Physics Letters 97 (18) 1-1 2010年

    DOI: 10.1063/1.3512958  

  174. 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 052008 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.

  175. 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 062019-1-062019-4 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.

  176. 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) 042505-1-042505-3 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.

  177. 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 042017-1-042017-4 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.

  178. 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 072104-1-072104-4 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.

  179. Polarized Raman study for epitaxial PZT thick film with the mixture orientation of (100)/(001) 査読有り

    Mitsumasa Nakajima, Takashi Fujisawa, Ken Nishida, Takashi Yamamoto, Minoru Osada, Hiroshi Naganuma, Soichiro Okamura, Hiroshi Funakubo

    ASIAN CERAMIC SCIENCE FOR ELECTRONICS III AND ELECTROCERAMICS IN JAPAN XII 421-422 99-+ 2010年

    出版者・発行元:TRANS TECH PUBLICATIONS LTD

    DOI: 10.4028/www.scientific.net/KEM.421-422.99  

    ISSN:1013-9826

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    (100)/(001)-oriented PZT thick films were grown on SrRuO3//(100) SrTiO3 and (100) MgO substrates by matel organic chemical vapor deposition (MOCVD) with different volume fraction of (001) orientation, and were compared with (001) single-oriented epitaxial PZT thick films grown on SrRuO3//LaNiO3//(100) CaF2 by polarized Raman spectroscopy. The spectra from (100)-oriented domain and (001)-oriented domain can be individually observed for the films with the mixture orientation of (100)/(001). Raman analysis revealed the different strain state of (100)-oriented and (001)-oriented domains. Moreover, the rotation dependence of A(1)(1TO) mode could be explained by the calculation using the volume fraction of (001)-oriented domains obtained from X-ray reciprocal space mapping analysis for the films with the mixture orientation of (100)/(001). These results suggest the local structure characterized by Raman spectroscopy almost agreed with the structure characterized by XRD analysis for the films with the mixture orientation of (100)/(001).

  180. 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.

  181. 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 052019-1-052019-5 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.

  182. 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 052018-1-052018-5 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.

  183. 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 052011-1-052011-5 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.

  184. 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 052009-1-052009-5 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.

  185. 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) 053002-1-053002-3 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

  186. Crystal Structures and Electrical Properties of Epitaxial BiFeO3 Thin Films with (001), (110), and (111) Orientations 査読有り

    Keita Sone, Hiroshi Naganuma, Takamichi Miyazaki, Takashi Nakajima, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 49 (9) 09MB03-1-09MB03-6 2010年

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.49.09MB03  

    ISSN:0021-4922

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    BiFeO3 (BFO) films were formed on (001), (110), and (111) La-doped SrTiO3 single-crystal substrates. All the films were epitaxially grown and had mainly rhombohedral structure. The BFO film formed on the (001) substrate had only a (001) component whereas the BFO films on (110) and (111) substrates had ((1) over bar 10) and ((1) over bar 11) components, respectively. The (001), (110), and (111) epitaxial BFO films showed the remanent polarizations of 63, 84, and 106 mu C/cm(2), respectively. It seems that the ((1) over bar 10) and ((1) over bar 11) components were changed to (110) and (111) ones, respectively, by applying an external voltage. The (001) epitaxial BFO film showed marked asymmetry in its electrical properties. It was found that the (001) epitaxial BFO film had a thin tetragonal layer with spontaneous polarization fixed in the downward direction near the substrate. Finally, we concluded that this tetragonal layer caused the accumulation of space charges at the interface, causing a downward built-in field to be generated. The downward build-in field facilitated the switching of upward polarization and caused asymmetric relaxation. (C) 2010 The Japan Society of Applied Physics

  187. 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 (12) 123001-1-123001-3 2010年

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.3.123001  

    ISSN:1882-0778

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    We have investigated magnetic field strength (up to 10 kOe) and angle dependences of spin dynamics in 4-nm-thick films of CoCrPt alloys with perpendicular magnetic anisotropy using the all-optical time-resolved magneto-optical Kerr effect (TRMOKE). The comprehensive TRMOKE measurements have indicated the Gilbert damping constant alpha of 0.05 for the alloy film with low coercivity. The experiments also indicated that alpha values for the alloy films deposited at higher temperatures with higher coercivities were also no greater than 0.06. (C) 2010 The Japan Society of Applied Physics

  188. Magnetic and Electronic Properties of BaTiO3-(Ni,Cu,Zn)Fe2O4 Ceramic Composite: Reflection of Kepler Conjecture 査読有り

    Kenji Kamishima, Yoshitaka Nagashima, Koichi Kakizaki, Nobuyuki Hiratsuka, Kowashi Watanabe, Hiroshi Naganuma

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (12) 124801-1-124801-5 2009年12月

    出版者・発行元:PHYSICAL SOC JAPAN

    DOI: 10.1143/JPSJ.78.124801  

    ISSN:0031-9015

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    Ceramic composites [xNi(0.15)Cu(0.3)nZn(0.55)Fe(2)O(4)-(1-x)BaTiO3] were successfully prepared by a direct solid-state reaction of raw materials (BaCO3, CuO, alpha-Fe2O3, NiO, TiO2, and ZnO). The composites are so homogeneous that the ferrite and BaTiO3 grains do not react with each other. The x-dependent permeability and permittivity are found to obey Maxwell-Garnett effective medium theory, which suggests that the composites consist of ferrite particles with barium titanate medium. This model, however, starts to deviate from the experimental data at x = 0.75, and the roles of medium and inclusions seem to be exchanged. It can be qualitatively explained by the fact that geometrical close-packing of spheres is limited up to about 74 vol% (Kepler conjecture).

  189. 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]

  190. 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.

  191. Optical Properties of BiFeO3-System Multiferroic Thin Films 査読有り

    Hiromi Shima, Takeshi Kawae, Akiharu Morimoto, Masahiro Matsuda, Michio Suzuki, Toshiyasu Tadokoro, Hiroshi Naganuma, Takashi Iijima, Takashi Nakajima, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 48 (9) 09KB01 2009年9月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.48.09KB01  

    ISSN:0021-4922

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    The optical properties of the chemical solution deposition (CSD)-derived BiFeO3 (BFO) film and the pulsed laser deposition (PLD)-derived (Bi,Nd)(Fe,Mn)O-3 (BNFM) film were evaluated by spectroscopic ellipsometry, and their optical constants (n, k) and band gaps were determined. At a wavelength of 600 nm, the refractive indexes of 3.22 and 2.87 were estimated for the BFO and BNFM films, respectively, although the existence of a refractive index gradient was suggested in the BFO film. In addition, at a wavelength of 1550 nm, which is generally used for optical communication, the refractive indexes of 2.91 and 2.59 were estimated for the BFO and BNFM films, respectively. The band gaps of the BFO and BNFM films were estimated to be 2.79 and 2.72 eV, respectively, and it was confirmed that the extinction coefficients of both films were almost zero at wavelengths larger than 600 nm. These results suggest that the BFO-system multiferroic films have a high potential as an optical material with a high refractive index. (C) 2009 The Japan Society of Applied Physics

  192. 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) 093001 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

  193. 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) 083002 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

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

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

    JAPANESE JOURNAL OF APPLIED PHYSICS 48 (8) 083002 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

  195. 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) 252503 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.

  196. Structural, magnetic, and ferroelectric properties of multiferroic BiFeO3-based composite films with exchange bias 査読有り

    Hiroshi Naganuma, Tomosato Okubo, Sho Sekiguchi, Yasuo Ando, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 105 (7) 07D9031-07D9033 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3055284  

    ISSN:0021-8979

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    BiFeO3-based composite films with excess iron content were fabricated, and the dependence of their magnetic and ferroelectric properties on the excess iron content was systematically investigated. Structural and magnetic analyses indicated that the specimens might be composed of large antiferromagnetic BiFeO3 grains and small ferromagnetic component. When the iron content was increased, saturation magnetization (M-s) increased and remanent polarization decreased. Antiferromagnetic coupling (H-ex) between the antiferromagnetic BiFeO3 grains and the ferromagnetic grains was observed at 10 K. It was revealed that grain growth is the key to increasing M-s and P-r and observing H-ex at room temperature in BiFeO3-based composite films. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3055284]

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

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

    JOURNAL OF APPLIED PHYSICS 105 (7) 07C911 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]

  198. Structural analysis of interfacial strained epitaxial BiMnO3 films fabricated by chemical solution deposition 査読有り

    Hiroshi Naganuma, Andras Kovacs, Tetsuro Harima, Hiromi Shima, Soichiro Okamura, Yoshihiko Hirotsu

    JOURNAL OF APPLIED PHYSICS 105 (7) 07D915-1-07D915-3 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3074096  

    ISSN:0021-8979

    eISSN:1089-7550

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    f An interfacial epitaxial BiMnO3 layer was fabricated by chemical solution deposition on SrTiO3 (100) substrate, and the microstructure of the film was analyzed by x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM). The TEM observation revealed the epitaxial growth of BiMnO3 on the SrTiO3 substrate as follows: ([110] (001)) BiMnO3 parallel to[0-10] x (001) SrTiO3. XRD and TEM analyses revealed that the mismatch between the epitaxial BiMnO3 and the SrTiO3 substrate causes a distortion in lattice parameters of BiMnO3 and, consequently, a large compressive strain in the BiMnO3 layer. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3074096]

  199. Influence of Pb and La Contents on the Lattice Configuration of La-Substituted Pb(Zr,Ti)O-3 Films Fabricated. by CSD Method 査読有り

    Hiromi Shima, Ken Nishida, Hiroshi Funakubo, Takashi Iijima, Takashi Katoda, Hiroshi Naganuma, Soichiro Okamura

    IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 56 (4) 687-692 2009年4月

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

    DOI: 10.1109/TUFFC.2009.1091  

    ISSN:0885-3010

    eISSN:1525-8955

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    The influence of Pb and La contents on the lattice configuration in La-substituted Pb(Zr-0.65,Ti-0.35)O-3 (La-PZT) films was systematically investigated. La-PZT films with various La and Pb contents were fabricated on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD). In the La-PZT films with a Pb content ratio of 125% relative to a stoichiometric value, La ions were substituted for not only A-site ions but also B-site ions at La contents greater than 3 mol%. La substitution for B-site seems to cause larger reduction of the unit cell size. In addition, we found that in the La-PZT films with a La content of 3 mol%, the Pb content of 116 mol% (120% relative to a stoichiometric value) was optimum from the viewpoint of site occupancy. This indicates that excess Pb prevented the A-site substitution of La ions.

  200. Co置換Biフェライト薄膜の室温での強誘電性および磁気特性 査読有り

    永沼博, 三浦淳, 神島謙二, 柿崎浩一, 平塚信之, 安藤康夫, 岡村総一郎

    Journal of Magnetic Society of Japan 33 (3) 237-241 2009年3月

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/msjmag.0903RC8081  

    ISSN:1882-2924

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    Co substituted BiFeO<sub>3</sub> polycrystalline films were fabricated on Pt/Ti/SiO<sub>2</sub>/Si(100) substrates by a chemical solution deposition method that was followed by post-deposition annealing between 673 and 1073 K. The substitution of cobalt at <i>B</i>-sites for iron in BiFeO<sub>3</sub> was promoted at relatively high temperatures, and saturated at around 923 K. The leakage current density was suppressed by substituting Co; therefore, ferroelectricity could be observed at room temperature. The remanent polarization increased by substituting Co due to the reduced electric coercive field. The saturation magnetization increased by promoting Co substitution, and a magnetic coercive field of 1.5 kOe and remanent magnetization of 3 emu/cm<sup>3</sup> were obtained by annealing at 923 K. This indicated that Co substituted BiFeO<sub>3</sub> films are candidate materials that enable ferromagnetism and ferroelectricity to coexist above room temperature.

  201. Composition control and thickness dependence of (100)-oriented epitaxial BiCoO3–BiFeO3 films grown by metalorganic chemical vapor deposition 査読有り

    Shintaro Yasui, Mitsumasa Nakajima, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Takashi Iijima, Masaki Azuma, Hitoshi Morioka, Keisuke Saito, Mutsuo Ishikawa, Tomoaki Yamada, Hiroshi Funakubo

    Journal of Applied Physics 105 (6) 061620-1-061620-5 2009年3月

    出版者・発行元:None

    DOI: 10.1063/1.3073824  

    ISSN:0021-8979

    eISSN:1089-7550

  202. 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) 122503 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).

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

    Takahide Kubota, Sumito Tsunegi, Mikihiko Oogane, Shigemi Mizukami, Terunobu Miyazaki, Hiroshi Naganuma, Yasuo Ando

    APPLIED PHYSICS LETTERS 94 (12) 122504-1-122504-3 2009年3月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3105982  

    ISSN:0003-6951

    eISSN:1077-3118

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    Transport properties in magnetic tunnel junctions (MTJs) with Co2FexMn1-xSi (CFMS, x=0-1.0)/Al-O/Co75Fe25 structure and Gilbert damping constant in the epitaxial CFMS films were investigated. The tunnel magnetoresistance ratio is as high as 75% in MTJs with x=0.6 at room temperature. The Gilbert damping constant is minimal at x=0.4. Relations between half-metallicity and the Gilbert damping constant in CFMS films were examined, revealing that the damping constant is small in half-metallic CFMS films.

  204. Fabrication of conductive oxide polycrystalline BaPbO3 films by chemical solution deposition and their electrical resistivity 査読有り

    Hiroshi Naganuma, Kayoko Yamada, Hiromi Shima, Kensuke Akiyama, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    JOURNAL OF ELECTROCERAMICS 22 (1-3) 78-81 2009年2月

    出版者・発行元:SPRINGER

    DOI: 10.1007/s10832-008-9426-1  

    ISSN:1385-3449

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    BaPbO3 films were fabricated by a chemical solution deposition on the SiO2/Si(100) and MgO(100) substrates followed by a post-deposition annealing at the temperatures between 673 and 1073 K under oxygen flow. Polycrystalline BaPbO3 films were formed together with secondary phases such as PbO and Pb3O4 onto MgO(100) substrates at around 750 K, and the films were crystallized into single phase of BaPbO3 above 823 K. Endothermic peak in differential thermal analysis due to crystallization of BaPbO3 was observed at 750 K, which is consistent with crystallization temperature of BaPbO3 estimated from X-ray diffraction. The electrical resistivity depended on the annealing temperature even in the single phase BaPbO3 films, the lowest resistivity of 3 x 10(-6) mu I (c)center dot m which was comparable to that of bulk BaPbO3 was achieved at the annealing temperature of 873 K.

  205. Annealing temperature effect on ferroelectric and magnetic properties in Mn-added polycrystalline BiFeO3 films 査読有り

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    JOURNAL OF ELECTROCERAMICS 22 (1-3) 203-208 2009年2月

    出版者・発行元:SPRINGER

    DOI: 10.1007/s10832-007-9400-3  

    ISSN:1385-3449

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    We fabricated 5 at.% Mn-added polycrystalline BiFeO3 films and investigated the annealing temperature effect on structural, ferroelectric and magnetic properties. In the x-ray diffraction patterns, only the diffraction peaks due to the BiFeO3 structure were observed and no secondary phase could be observed at annealing temperatures between 773 and 923 K. Adding Mn suppressed the leakage current density in the high electric field region when compared to pure BiFeO3 films. The conduction mechanism of the Mn-added BiFeO3 films was dominated by Ohmic conduction. Remanent polarization of the Mn-added polycrystalline BiFeO3 films for an applied electric field of approximately 1.5 mV/cm was 63 mu C/cm(2) for the specimen annealed at 773 K and 46 mu C/cm(2) for the specimen annealed at 923 K, although the remanent polarization still exhibited a tendency to increase with an increase in the electric field. Spontaneous magnetization was obtained at high annealing specimens. This study revealed that the annealing temperature strongly affected the ferroelectric and magnetic properties in Mn-added polycrystalline BiFeO3 films. In addition, by optimizing the annealing temperature, we realized multiferroics coexistent with spontaneous magnetization and spontaneous polarization at room temperature in the Mn-added polycrystalline BiFeO3 film.

  206. Tunnel magnetoresistance effect in double magnetic tunnel junctions using half-metallic Heusler alloy electrodes

    Ohdaira, Y., Oogane, M., Ando, Y.

    Journal of Applied Physics 105 (7) 2-2 2009年

    DOI: 10.1063/1.3072023  

  207. Tunnel magnetoresistance effect in double magnetic tunnel junctions using half-metallic Heusler alloy electrodes

    Hiroshi Naganuma

    Journal of Applied Physics 2009年

    DOI: 10.1063/1.3072023  

  208. Piezoelectric Endurance Properties of Lead Zirconate Titanate Thick Films for Micro-Device Applications 査読有り

    Takashi Iijima, Yuji Kobayashi, Hiroshi Naganuma, Soichiro Okamura

    FERROELECTRICS 389 49-54 2009年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/00150190902987715  

    ISSN:0015-0193

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    The effect of pulse switching on the piezoelectric response of 10-mu m-thick Pb(Zr(0.53)Ti(0.47))O(3) films was investigated. The amount of the longitudinal displacement related with piezoelectric response decreases when the bipolar pulse switching count is greater than 10(7). This degradation tendency is consistent with the "fatigue" profile for remanent polarization of the PZT films. However, longitudinal displacement degradation was not observed for unipolar pulse switching. These experimental results suggest that the unipolar drive of the high electrical field does not affect the displacement endurance property of the PZT thick films for micro-actuator application.

  209. The Optical Property of Multiferroic BiFeO3 Films 査読有り

    Hiromi Shima, Hiroshi Naganuma, Takashi Iijima, Takashi Nakajima, Soichiro Okamura

    INTEGRATED FERROELECTRICS 106 11-16 2009年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/10584580903212763  

    ISSN:1058-4587

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    We fabricated a multiferroic BiFeO3 (BFO) film and evaluated its optical properties. A polycrystalline BFO film with a thickness of 650 nm was formed on a Pt/Ti/SiO2/Si substrate. The refractive index of the BFO film was estimated to be approximately 3.0 at a wavelength of 600 nm. This value is the largest in the visible light range for oxide films such as rutile-type TiO2. Furthermore, the extinction coefficient was estimated to be zero in the wavelength range of 600 to 1670 nm. These results suggest that the produced BFO film is a promising material for optical communication devices.

  210. Annealing temperature dependences of ferroelectric and magnetic properties in polycrystalline Co-substituted BiFeO3 films 査読有り

    Hiroshi Naganuma, Jun Miura, Mitsumasa Nakajima, Hiromi Shima, Soichiro Okamura, Shintaro Yasui, Hiroshi Funakubo, Ken Nishida, Takashi Iijima, Masaki Azuma, Yasuo Ando, Kenji Kamishima, Koichi Kakizaki, Nobuyuki Hiratsuka

    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (9) 7574-7578 2008年9月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.47.7574  

    ISSN:0021-4922

    eISSN:1347-4065

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    Multiferroic Co-substituted BiFeO3 films were fabricated by chemical solution deposition method followed by post deposition annealing at various temperatures. The substitution of Cobalt of B-sites for iron in BiFeO3 was promoted at relatively high temperatures. The B-site substitution by cobalt promoted increases in saturation magnetization and spontaneous magnetization By substitution. leakage Current density Was suppressed ill a high-electric-field region and ferroelectric hysteresis (P-E) loops became measurable even at room temperature. The optimal annealing temperature for the coexistence of a high remanent polarization and a high remanent magnetization was 923 K having a high B-site substitution ratio of cobalt.

  211. Crystal Structure and Electrical Properties of -Oriented Epitaxial BiCoO3–BiFeO3 Films Grown by Metal Organic Chemical Vapor Deposition 査読有り

    Shintaro Yasui, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Takashi Iijima, Masaki Azuma, Hitoshi Morioka, Keisuke Saito, Mutsuo Ishikawa, Tomoaki Yamada, Hiroshi Funakubo

    Japanese Journal of Applied Physics 47 (9) 7582-7585 2008年9月

    出版者・発行元:None

    DOI: 10.1143/JJAP.47.7582  

    ISSN:0021-4922

  212. Electrooptic and piezoelectric properties of (Pb,La)(Zr,Ti)O-3 films with various Zr/Ti ratios 査読有り

    Hiromi Shima, Takashi Iijima, Hiroshi Funakubo, Takashi Nakajima, Hiroshi Naganuma, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (9) 7541-7544 2008年9月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.47.7541  

    ISSN:0021-4922

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    A systematic investigation of the electrooptic properties of (Pb,La)(Zr,Ti)O-3 (PLZT) films was carried out. 700-nm-thick polycrystalline PLZT films with 2 mol % La and various Zr/Ti ratios were formed on Pt/Ti/SiO2/Si substrates, and their reflectance spectra were measured. Zr/Ti ratio significantly affected the surface morphology of the films, and PLZT films with what Ti/(Zr + Ti) ratios ranging from 40 to 70% showed less reflectance light loss that because of their smooth surface. The maximum resonant wavelength shift was attained at a Ti/(Zr + Ti) ratio of 40%. These results suggest that the PLZT film with a Ti/(Zr + Ti) ratio of 40% is optimum for application in optical devices such as a spatial light modulator (SLM). The piezoelectric properties of the PLZT films were also evaluated because their resonant wavelength shift Was caused by changes in not only refractive index but also film thickness. The piezoelectric displacement showed a maximum Ti/(Zr + Ti) ratio of 10% and monotonically decreased with increasing Ti/(Zr + Ti) ratio in our PLZT films. The exact Pockels coefficient of the PLZT(2/60/40) film was estimated to he 104 pm/V at 600 nm by subtracting the effect of the change in film thickness from the resonant wavelength shift.

  213. Composition dependence in BiFeO3 film capacitor with suppressed leakage current by Nd and Mn cosubstitution and their ferroelectric properties 査読有り

    Takeshi Kawae, Hisashi Tsuda, Hiroshi Naganuma, Satoru Yamada, Minoru Kumeda, Soichiro Okamura, Akiharu Morimoto

    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (9) 7586-7589 2008年9月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/JJAP.47.75861  

    ISSN:0021-4922

    eISSN:1347-4065

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    (Nd,Mn)-cosubstituted BiFeO3 (BFO) films with various Nd and Mn compositions were fabricated on a Pt/SrTiO3 (100) substrate by pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy images indicated that the suppression of impurity phases and a smooth surface morphology were realized by Nd substitution in the BFO films. Furthermore, by combining with Nd substitution, a small amount of Mn substitution in BFO films is effective for reducing the leakage current density by three orders of magnitute compared with that of a BFO film capacitor. The polarization vs electric field (P-E) curves showed a strong dependence of measurement frequency in the range of 0.1-2 kHz, and well-saturated P-E hysteresis loops were observed at 20 kHz at room temperature. The remenent polarization and coercive field at a maximum electric field of 1.9 MV/cm were approximaterly 70 mu C/cm(2) and 0.32 MV/cm, respectively.

  214. Ferroelectric, electrical and magnetic properties of Cr, Mn, Co, Ni, Cu added polycrystalline BiFeO(3) films 査読有り

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    APPLIED PHYSICS LETTERS 93 (5) 052901-1-052901-3 2008年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2965799  

    ISSN:0003-6951

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    Cr, Mn, Co, Ni, and Cu were added to polycrystalline BiFeO(3) films, and their influence on the ferroelectric, electrical, and magnetic properties was investigated. All the additives except Ni reduced the leakage current density in the high electric field region. The addition of Cu and Co decreased the coercive field without reducing remanent polarization. The addition of Co caused spontaneous magnetization at room temperature, which exhibited a large coercive field of 16 kOe at 10 K. It was revealed that Co addition suppressed the leakage current density, decreased the electric coercive field, and induced spontaneous magnetization and large magnetic coercivity. (C) 2008 American Institute of Physics.

  215. Estimation of leakage current density and remanent polarization of BiFeO3 films with low resistivity by positive, up, negative, and down measurements 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (7) 5558-5560 2008年7月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.47.5558  

    ISSN:0021-4922

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    Polycrystalline BiFeO3 film was fabricated by chemical solution deposition (CSD) on 111-textured Pt/Ti/SiO2,/Si(100) substrates followed by post-annealing at 923 K in air. The leakage current density was estimated by pulse response of a positive, up, negative, and down (PUND) measurement. It was revealed that the leakage current density estimated by PUND measurements is useful for high leakage current materials because the dielectric breakdown could be extended to the high electric field region when compared to a conventional measurement way using a pico-ampere meter. Therefore, the changing point of the leakage current mechanism at the higher electric field of 0.3 MV/cm could be observed by using the PUND method in the present specimen. When the temperature was decreased. it was revealed that the leakage current component did not affect the ferroelectric polarization below 150 K in the case of present specimen. At 93 K. where leakage current was suppressed, the remanent polarizations were evaluated by ferroelectric hysteresis loops and PUND, and it was revealed that the remanent polarization did not saturate until an electric field of 1.4MV/cm was applied (P-r = 89 mu C/cm(2) at P-E loop, 2P(r) = 164 mu C/cm(2) at PUND). This result indicates the potential of BiFeO3 to have quite high remanent polarization.

  216. Evaluation of electrical properties of leaky BiFeO(3) films in high electric field region by high-speed positive-up-negative-down measurement 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    APPLIED PHYSICS EXPRESS 1 (6) 061601 2008年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.1.061601  

    ISSN:1882-0778

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    The electrical properties of leaky ferroelectric BiFeO(3) thin films were evaluated by using a high-speed positive-up-negative-down (PUND) measurement technique. The leakage current density was estimated from the gradient of the pulse response when a constant electric field was applied. The relative permittivity was estimated from an abrupt decrement when the applied field was removed. The twofold remanent polarization without the influence of the leakage current was estimated by subtracting the contribution of a paraelectric component from the abrupt increment in the pulse response when a positive pulse was applied. (C) 2008 The Japan Society of Applied Physics.

  217. Simple process synthesis of BaTiO3-(Ni,Zn,Cu)Fe2O4 ceramic composite 査読有り

    Kenji Kamishima, Yoshitaka Nagashima, Koichi Kakizaki, Nobuyuki Hiratsuka, Kowashi Watanabe, Takaya Mise, Hiroshi Naganuma, Soichiro Okamura

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6) 064801-1-064801-4 2008年6月

    出版者・発行元:PHYSICAL SOC JAPAN

    DOI: 10.1143/JPSJ.77.064801  

    ISSN:0031-9015

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    Ceramic composites (2Ni(0.41)Zn(0.41)Cu(0.18)Fe(2)O(4)-BaTiO3) were successfully prepared by a direct solid-state reaction of raw materials (BaCO3, CuO, alpha-Fe2O3, NiO, TiO2, and ZnO). X-ray diffraction (XRD) and electron probe micro analysis (EPMA) measurements were performed for these samples and it is confirmed that the composites consist of spinel ferrite and BaTiO3 phases. The composites are so homogeneous that the ferrite and BaTiO3 grains do not react with each other and have radii in the range of 1-5 mu m. Hexagonal BaTiO3 (h-BaTiO3) can be made in this composite form with a sintering temperature of 1200 degrees C, although h-BaTiO3 can be usually synthesized above 1460 degrees C. The freezing-point depression of BaTiO3 takes place due to the mixing with the spinel ferrite, which may result in the formation of h-BaTiO3 at a low temperature of 1200 degrees C.

  218. (Ni,Cu,Zn)Fe2O4-BaTiO3 共存材料の構造および物性 査読有り

    長島 義嵩, 神島 謙二, 柿崎 浩一, 平塚 信之, 永沼 博, 岡村 総一郎

    Journal of the Magnetics Society of Japan 32 (3) 250-253 2008年5月

    出版者・発行元:公益社団法人日本磁気学会

    DOI: 10.3379/msjmag.32.250  

    ISSN:1882-2924

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    Ceramic composites (x Ni<sub>0.15</sub>Cu<sub>0.3</sub>Zn<sub>0.55</sub>Fe<sub>2</sub>O<sub>4</sub> + (1-x) BaTiO<sub>3</sub>) were prepared by a conventional ceramic method. X-ray diffraction (XRD) and electron probe micro analysis (EPMA) measurements were performed for these samples and it is confirmed that the composites consist of spinel ferrite and BaTiO<sub>3</sub> phases. The composites are so homogeneous that the ferrite and BaTiO<sub>3</sub> grains do not react to each other and have radii of 1-5 um. The resonant frequency in initial permeability and permittivity is increased by increasing the amount of BaTiO<sub>3</sub>.

  219. Ferroelectric and magnetic properties of multiferroic BiFeO3-Based composite films 査読有り

    Hiroshi Naganuma, Tomosato Okubo, Kenji Kamishima, Koichi Kakizaki, Nobuyuki Hiratsuka, Soichiro Okamura

    IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 55 (5) 1051-1055 2008年5月

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

    DOI: 10.1109/TUFFC.2008.755  

    ISSN:0885-3010

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    BiFeO3-based composite films were fabricated onto the Pt/Ti/SiO2/Si(100) substrates by a chemical solution deposition (CSD) method using the precursor solutions with various excess iron composition followed by annealing at 923 K for 30 minutes under oxygen gas flow. Coexistence of spontaneous magnetization and remanent polarization could be obtained in the BiFeO3-based composite films with high excess iron composition. The remanent magnetization of almost 20 emu/cm(3) and the magnetic coercive field of 1.5 kOe were obtained at the iron composition ratio of Fe/Bi = 1.25. In this specimen, the remanent polarization at 90 K was approximately 10 mu C/cm(2) at the electric field of 1500 kV/cm. Structural analysis suggested that the remanent polarization has a possibility to increase by suppressing the formation of the secondary phases of Bi2Fe4O9 and alpha-Fe2O3, these are the nonferroelectric material as well as antiferromagnetic phase.

  220. Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO3 films 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 55 (5) 1046-1050 2008年5月

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

    DOI: 10.1109/TUFFC.2008.754  

    ISSN:0885-3010

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    A multiferroic BiFeO3 film was fabricated on a Pt/Ti/SiO2/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO3 film. A high remanent polarization of 89 mu C/cm(2) was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm(3) at room temperature and increased to approximately 2 emu/cm(3) at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO3 film were nonlinear at both temperatures, which is different with BiFeO3 single crystal.

  221. Enhancement of ferroelectric and magnetic properties in BiFeO(3) films by small amount of cobalt addition 査読有り

    Hiroshi Naganuma, Nozomi Shimura, Jun Miura, Hiromi Shima, Shintaro Yasui, Ken Nishida, Takashi Katoda, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 103 (7) 07E314 2008年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2836971  

    ISSN:0021-8979

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    Both the ferroelectric and magnetic properties of polycrystalline BiFeO(3) films fabricated by chemical solution deposition were enhanced by adding small amounts of cobalt. Addition of 3 at. % cobalt to BiFeO(3) films increased the remanent polarization from 49 to 72 mu C/cm(2) and decreased the electric coercive field from 0.54 to 0.44 MV/cm. The ferroelectricity degraded when the cobalt concentration exceeded 9 at. % due to the formation of the secondary phases of Bi(2)Pt. The saturation magnetization was drastically enhanced by the addition of cobalt up to 12 at. %. This is because the magnetic moments are not canceled locally since the differences of magnetic moment between B-sites. The saturation magnetization decreased when the cobalt content exceeded 15 at. %, thereby attributing to the formation of a nonmagnetic secondary phase of Bi(2)Pt. It is concluded that both ferroelectric and magnetic properties were enhanced, provided only small amount of cobalt were added to the films.

  222. Effect of 3d Transition Metals Addition on the Ferroelectric Properties in Bi Ferrite Thin films 査読有り

    H. Naganuma, J. Miura, S. Okamura

    JOURNAL OF MATERIALS RESEARCH in press 2008年

  223. Imprint behavior of ferroelectric Pb(ZrTi)O-3 thin-film capacitors in the early stage 査読有り

    Soichiro Okamura, Soichiro Koshika, Hiromi Shima, Hroshi Naganuma

    INTEGRATED FERROELECTRICS 96 90-99 2008年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/10584580802101075  

    ISSN:1058-4587

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    Imprint behavior of Pb(Zr,Ti)O-3 (PZT) thin-film capacitors in the early stage was carefully measured. The PZT films were formed on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) with sintering at 700C, and a post-annealing was carried out at the same temperature after the deposition of top Pt electrodes by rf-magnetron sputtering. The imprint progresses of the PZT thin-film capacitors could be fitted by three equations with the same form, V-shift = V-0 ln (1 + t/tau), but three diferent sets of parameters; V-0 and . This indicates that the conduction mechanisms of space charges which caused imprint changed by three steps with time progress. The first mechanism had less temperature dependence while the second one had remarkable temperature dependence. Whether the third one had temperature dependence or not was not clear because of data points were too few, it impacted a longtime imprint. From these results, we speculated that the imprint progresses were controlled by charge injection from electrodes due to first Fowler-Nordheim and seconde Schottky-emission in interfacial layers, and finally Poole-Frenkel conduction in film bodies.

  224. Crystal Structure Analysis of Epitaxial BiFeO3–BiCoO3 Solid Solution Films Grown by Metalorganic Chemical Vapor Deposition 査読有り

    Shintaro Yasui, Ken Nishida, Hiroshi Naganuma, Soichiro Okamura, Takashi Iijima, Hiroshi Funakubo

    Japanese Journal of Applied Physics 46 (10B) 6948-6951 2007年10月

    出版者・発行元:None

    DOI: 10.1143/JJAP.46.6948  

    ISSN:0021-4922

  225. Structural analysis of polycrystalline BiFeO3 films by transmission electron microscopy 査読有り

    Hiroshi Naganuma, Andras Kovacs, Akihiko Hirata, Yoshihiko Hirotsu, Soichiro Okamura

    MATERIALS TRANSACTIONS 48 (9) 2370-2373 2007年9月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW200782  

    ISSN:1345-9678

    eISSN:1347-5320

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    A multiferroic polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO3 film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO3 has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO3 film shows the small saturation magnetization of 5.2emu/cm(3) without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO3 film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 mu C/cm(2) and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.

  226. Structural, magnetic, and ferroelectric properties of multiferroic BiFeO3 film fabricated by chemical solution deposition 査読有り

    Hiroshi Naganuma, Soichiro Okamura

    JOURNAL OF APPLIED PHYSICS 101 (9) 09M103-1-09M103-3 2007年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2711279  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition on Pt/Ti/SiO2/Si(100) substrates. A ferroelectric hysteresis loop showed a high remanent polarization of 47 mu C/cm(2) at room temperature. Leakage current density was on the order of 10(-1) A/cm(2) at 100 kV/cm, indicating the high leakage current density in the present BiFeO3 film. The leakage current mechanism could be considered as follows: Ohmic conduction at low electric field and Poole-Frenkel trap-assisted conduction appeared as the electric field increased, and space-charge-limited current started at a high electric field. Weak ferromagnetism was observed at room temperature, and magnetic coercivity increased to 0.5 kOe with small remanent magnetization of 2 emu/cm(3) at 10 K. In order to investigate the magnetoelectric effect of the BiFeO3 film, the ferroelectric hysteresis loop was measured under the magnetic field of 5 kG at room temperature. (c) 2007 American Institute of Physics.

  227. Particle size dependence of atomic ordering and magnetic properties of L1(0)-FePd nanoparticles 査読有り

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 2356-2358 2007年3月

    出版者・発行元:ELSEVIER

    DOI: 10.1016/j.jmmm.2006.11.104  

    ISSN:0304-8853

    eISSN:1873-4766

    詳細を見る 詳細を閉じる

    L1(0)- type FePd nanoparticles with mean sizes between 4 and 15nm in diameter have been fabricated by electron beam evaporation. Coercivity and remanence of FePd nanoparticles with sizes less than about 8 nm were quite low compared to the values for 10- nm- sized FePd nanoparticles. Both coercivity and remanence increased with decreasing the temperature, indicating the large suppression of the thermal agitation of the magnetic moment at lower temperatures. Superparamagnetic behavior appeared in zero-field- cooled ( ZFC) and field- cooled ( FC) temperature dependence of magnetization for about 6- nm- sized FePd nanoparticles. Disappearance of the hard magnetic properties in smaller sized FePd nanoparticles is attributed to the reduction of the long- range order ( LRO) parameter of the L10- structure as well as the thermal agitation of magnetic moment. (c) 2006 Elsevier B. V. All rights reserved.

  228. La Content Dependence of Piezoelectric Properties of Polycrystalline (Pb, La)(Zr0.65, Ti0.35)O3 Films 査読有り

    Hiromi Shima, Ken Nishida, Hiroshi Funakubo, Tadashi Iijima, Hiroshi Naganuma, Soichiro Okamura

    Transactions of the Materials Research Society of Japan 32 79-82 2007年3月

  229. Preparation and Characterization of Multiferroic BiFeO3 Films 査読有り

    Hiroshi Naganuma, Andras Kovacs, Yirotsu Hirotsu, Yosuke Inoue, Soichiro Okamura

    Transactions of Materials Research Society of Japan 32 39-42 2007年3月

  230. A new error backpropagation learning algorithm for a layered neural network with nondifferentiable units

    Naganuma, H., Ohori, T., Watanabe, K.

    Electronics and Communications in Japan Part Iii-Fundamental Electronic Science 90 (5) 2007年

    DOI: 10.1002/ecjc.20318  

  231. A new error backpropagation learning algorithm for a layered neural network with nondifferentiable units

    Hiroshi Naganuma

    Electronics and Communications in Japan Part Iii-fundamental Electronic Science 2007年

    DOI: 10.1002/ECJC.20318  

  232. Temperature dependence of ferroelectric and magnetic properties in polycrystalline BiFeO(3) films 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    2007 SIXTEENTH IEEE INTERNATIONAL SYMPOSIUM ON THE APPLICATIONS OF FERROELECTRICS, VOLS 1 AND 2 431-433 2007年

    出版者・発行元:IEEE

    ISSN:1099-4734

    詳細を見る 詳細を閉じる

    A BiFeO(3) film was fabricated by a chemical solution deposition (CSD) method onto the Pt/Ti/SiO(2)/Si(100) substrate followed by a post-deposition annealing at 973 K for 10 min in air. An x-ray diffraction measurement indicates the formation of the polycrystalline single phase of the BiFeO(3) film. The high remanent polarization of 89 mu C/cm(2) was observed at 90 K together with the relatively low electric coercive field of 380 kV/cm, though the ferroelectric hysteresis loops could not be observed at room temperature due to the high leakage current density. Magnetic measurements indicate that the low remanence magnetization of around 2 emu/cm(3) and the magnetic coercivity field of around 0.5 kOe were obtained at room temperature. These magnetic parameters increased around twice the value by decreasing the temperature to 100 K.

  233. Structural and ferroelectric properties of BiFeO3-BiCoO3 solid solution films 査読有り

    Hiroshi Naganuma, Nozomi Shimura, Hiromi Shima, Shintaro Yasui, Ken Nishida, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    2007 SIXTEENTH IEEE INTERNATIONAL SYMPOSIUM ON THE APPLICATIONS OF FERROELECTRICS, VOLS 1 AND 2 428-+ 2007年

    出版者・発行元:IEEE

    DOI: 10.1109/ISAF.2007.4393288  

    ISSN:1099-4734

    詳細を見る 詳細を閉じる

    BiFeO3-BiCoO3 solid solution films were fabricated by a chemical solution deposition (CSD) method onto the Pt/Ti/SiO2/Si(100) substrates followed by a post-deposition annealing at 873 K for 10 min. X-ray diffraction measurements indicate the apparent phase transition of the Bi(CoxFe1-x,)O-3 solid solution films by increasing the cobalt composition were take place at the cobalt composition of around x=0.2 and 0.4, respectively. According to the D-E hysteresis measurements, the ferroelectricity observed at the cobalt composition less than x=0.3 indicating that the MPB has a possibility to exist at these composition region.

  234. Preparation and characterization of Bi-perovskite oxide films for piezo applications 査読有り

    Shintaro Yasui, Hiroshi Naganuma, Soichiro Okamura, Takashi Iijima, Ken Nishida, Takashi Katoda, Hiroshi Uchida, Seiichiro Koda, Hiroshi Funakubo

    2007 SIXTEENTH IEEE INTERNATIONAL SYMPOSIUM ON THE APPLICATIONS OF FERROELECTRICS, VOLS 1 AND 2 102-+ 2007年

    出版者・発行元:IEEE

    DOI: 10.1109/ISAF.2007.4393180  

    ISSN:1099-4734

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    Thin films of BiFeO3-BiScO3 (BFO-BSO) solid-solution were fabricated for improving electrical resistivity of BiFeO3-based films by replacing electrically-unstable Fe3+ for stable Sc3+. The films with chemical composition of Bi(Fe1-x, Sc-x)O-3 were fabricated on (111)Pt/TiO2/SiO2/(100)Si by chemical solution deposition technique. Single phase of perovskite was obtained in the range of x = 0-0.3, where selective replacement of Fe3+ and Sc3+ was confirmed by Raman measurement. The leakage current density of BFO-BSO film was reduced by increasing x. Well-saturated polarization - electric field hysteresis loop was obtained for BFO-BSO film with x = 0. 15.

  235. Optimization of Pb content in a precursor solution for the fabrication of (Pb,La)(ZrTi)O-3 films for optical applications by chemical solution deposition 査読有り

    Hiromi Shima, Hiroshi Naganuma, Yukihiro Ishii, Akira Takashima, Soichiro Okamura

    FERROELECTRICS 357 223-227 2007年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/00150190701544840  

    ISSN:0015-0193

    eISSN:1563-5112

    詳細を見る 詳細を閉じる

    400-nm-thick (Pb,La)(ZrTi)O-3 (PLZT) films with a composition of Pb:La:Zr:Ti= X:3:65:35 were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates at 700 degrees C by chemical solution deposition using precursor solutions with Pb contents of X = 107, 112, 116, 121 and 126. The PUT films fabricated from the solutions of X = 107 and 112 had bimodal structure and included pyrochlore phase. The pyrochlore region decreased with increasing the Pb content, and single perovskite phase PLZT films with well-filled structure were obtained at the Pb contents of 121 and 126. From these results, we concluded that the lob-content of X = 121 (125 mol% relative to a stoichiometric value) was optimum for the fabrication of PUT films for optical applications. This optimization slightly improved electrical and electrooptic properties of the PUT films, and finally the PLZT(121/3/65/35) film showed the Pockels coefficient of 84 pm/V.

  236. Systematic fabrication of (Ba,Sr)TiO3 microdots with various Ba/Sr ratios by ink-jet printing and their evaluation 査読有り

    Soichiro Okamura, Hiromi Shima, Hiroshi Naganuma, Junji Musha, Tadashi Shiosaki

    FERROELECTRICS 357 3-8 2007年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/00150190701527258  

    ISSN:0015-0193

    eISSN:1563-5112

    詳細を見る 詳細を閉じる

    Systematic fabrication of (Ba,Sr)TiO3 microdots with different compositions was examined by ink-jet printing from two precursor solutions for BaTiO3 and SrTiO3, and subsequent heat treatment at 700 degrees C. The microdots were prepared by 40-times-overlapped discharging of the precursor solutions, and the composition of each microdot was adjusted by changing the shot number ratios of the two solutions. Relatively flat microdots with a width of approximately 100 Am and a thickness of approximately I mu m were formed by depositing self-assembled monolayer films on the substrate surface before discharge. Finally, 41 types of (Ba,Sr)TiO3 microdots with different compositions were successfully fabricated simultaneously on a Pt/Ti/SiO2/Si substrate, and the microdots were confirmed by Raman spectroscopy to have structures corresponding to the Ba/Sr ratios.

  237. [国際会議proceedings] Ferroelectric and Magnetic Properties of Multiferroic FeOx-BiFeO3 Composite Films’ 査読有り

    Hiroshi Naganuma, Tomosato Okubo, Soichiro Okamura

    Proceedings of the 16th International Symposium on the Application of Ferroelectrics 28PS 434-436 2007年

    出版者・発行元:None

    DOI: 10.1109/ISAF.2007.4393290  

    ISSN:1099-4734

  238. [国際会議proceedings] Influence of Pb and La Contents on the Lattice Configuration of La-Substituted Pb(Zr0.65, Ti0.35)O3 Films 査読有り

    Hiromi Shima, Ken Nishida, Hiroshi Funakubo, Takashi Iijima, Takashi Katoda, Hiroshi Naganuma, Soichiro Okamura

    Proceedings of the 16th International Symposium on the Application of Ferroelectrics 29PS 87-+ 2007年

    出版者・発行元:None

    DOI: 10.1109/ISAF.2007.4393175  

    ISSN:1099-4734

  239. [国際会議proceedings] Leakage Current Property of Pb(Zr0.4,Ti0.6)O3 Thin Film Capacitors with High Rectangular Hysteresis Property 査読有り

    Soichiro Okamura, Mitsumasa Tanimura, Hiromi Shima, Hiroshi Naganuma

    Proceedings of the 16th International Symposium on the Application of Ferroelectrics 29PS 91-93 2007年

    出版者・発行元:None

    ISSN:1099-4734

  240. Bi concentration dependence of structural, ferroelectric and magnetic properties of BiFeO3 films 査読有り

    Hiroshi Naganuma, Tomosato Okubo, Soichiro Okamura

    INTEGRATED FERROELECTRICS 95 234-241 2007年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/10584580701759429  

    ISSN:1058-4587

    詳細を見る 詳細を閉じる

    Bi-rich BiFeO3 films were fabricated by chemical solution deposition followed by a post-deposition annealing at 823 K in air. Not only the polycrystalline BiFeO3 phase but also the bismuth oxide phases were formed at high excess Bi contents. This suggested that the Bi atoms were not significantly evaporated. The remanent polarization decreased as the excess Bi contents increased at 90 K, though the remanent polarization of 33 mu C/cm(2) was still obtained at the excess Bi contents of 30 at.%. The magnetization monotonically decreased as the excess Bi content increased. It could be considered that the optimal Bi content is the stoichiometric value of BiFeO3 in the preparing way of the CSD followed by the annealing at 823 K.

  241. Leakage current mechanism of polycrystalline BiFeO3 films with Pt electrode 査読有り

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    INTEGRATED FERROELECTRICS 95 242-247 2007年

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/10584580701759395  

    ISSN:1058-4587

    詳細を見る 詳細を閉じる

    Leakage current mechanism of the polycrystalline BiFeO3 film annealing at 923 K with Pt electrodes was discussed based on Schottky-emission conduction, Poole-Frenkel trap limited conduction, Fowler-Nordheim tunneling conduction and space charge limited current (SCLC). The leakage cur-rent mechanism at room temperature is as follows; Schottky-emission or Poole-Frenkel was the candidate leakage current mechanism at low electric field and then leakage current mechanism was changed to the SCLC at high electric field. When decreasing the measuring temperature, the leakage current mechanism at low electric field was Poole-Frenkel trap limited conduction, though the electric field region of the PF trap limited conduction was much broader than that of the room temperature.

  242. Perpendicular magnetic anisotropy of epitaxially grown L1 <inf>0</inf>-FePdCu nanoparticles with preferential c -axis orientation 査読有り

    Naganuma, H., Sato, K., Hirotsu, Y.

    Journal of Applied Physics 100 (7) 174914 2006年10月13日

    DOI: 10.1063/1.2357420  

  243. Perpendicular magnetic anisotropy of epitaxially grown L1(0)-FePdCu nanoparticles with preferential c-axis orientation 査読有り

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    JOURNAL OF APPLIED PHYSICS 100 (7) 2006年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2357420  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Oriented and well-isolated 14-nm-sized Fe41Pd52Cu7 ternary alloy nanoparticles with the L1(0)-type ordered structure have been fabricated by the sequential deposition of Pd, Cu, and Fe on NaCl (001) substrate followed by postdeposition annealing. The annealing temperature required to obtain a high coercivity decreased by at least 50 K upon the addition of a small amount of Cu. Furthermore, it was revealed that a strong preferential c-axis orientation along the film normal direction was achieved by the addition of Cu, which resulted in a strong perpendicular magnetic anisotropy. The population of the nanoparticles with their c-axis oriented normal to the film plane was 74%. The alloy composition was independent of the particle size, as determined by energy dispersive x-ray spectroscopy using nanoprobe electrons. Nanobeam electron diffraction revealed that the axial ratio is constant for FePdCu nanoparticles with sizes between 10 and 25 nm. Interparticle magnetostatic and exchange interactions played an insignificant role in the isolated FePdCu nanoparticles. The correlation between their preferential c-axis orientation and magnetic properties is discussed based on the rotation magnetization of single magnetic domain particles. (c) 2006 American Institute of Physics.

  244. La content dependence of electrooptic properties of polycrystalline (Pb,La)(Zr-0.65,Ti-0.35)O-3 thick films 査読有り

    Hiromi Shima, Hiroshi Naganuma, Soichiro Okamura

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (9B) 7279-7282 2006年9月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.45.7279  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    The systematic investigation of the electrical, optical and electrooptic properties of lanthanum-substituted lead zirconate titanate (PLZT) films was carried out. Polycrystalline PLZT films with various La and Ph contents were prepared at various sintering temperatures by chemical solution deposition (CSD). Among the 135 conditions we examined, a sintering temperature of 700 degrees C and a Ph content ratio of 125% relative to a stoichiometric value were optimum for preparing well-filled films. The maximum polarization monotonically decreased with increasing La content, while the dielectric constant change was maximum at a La content of 6 mol %. The refractive indexes of the PLZT films were estimated to be in the range from 2.35 to 2.42 at 630 nm. The refractive index change due to the application of a DC bias voltage was maximum at a La content of 0 mol %, monotonically decreased with increasing La content, and strongly correlated with the maximum polarization change. Therefore, we concluded that the electrooptic effect in the PLZT films is mainly caused by the reconfiguration of the domain structure in the films.

  245. Direct synthesis of oriented high-density islands of L1(0)-FePtCu alloy at 613 K 査読有り

    Han Wool Ryu, Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 (20-23) L608-L610 2006年6月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.45.L608  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    A low-temperature synthesis of isolated and oriented L1(o)-FePtCu nanoparticles with high-density dispersion has been achieved by a conventional rf magnetron sputtering technique with a single crystal NaCl substrate. Hard magnetic L1(0)-type ordered phase with a coercivily of about 1.4 kOe is directly formed at substrate temperatures as low as 613 K without any post-deposition annealing. With a decrease in sputtering duration, particle size and interparticle distance decrease. These nanoparticles have (100) orientation on the NaCl substrate. The alloy compositional change from particle to particle is quite small. Although the atomic ordering is confirmed even at 563 K, the intensity of the superlattice reflections is very weak. The thermal fluctuation of magnetization becomes prominent in specimens with particle size smaller than about 10 nm in diameter.

  246. Fabrication of oriented L1(0)-FeCuPd and composite bcc-Fe/L1(0)-FeCuPd nanoparticles: Alloy composition dependence of magnetic properties 査読有り

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    JOURNAL OF APPLIED PHYSICS 99 (8) 08N706 2006年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2165604  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Oriented and well-isolated L1(0)-FeCuPd ternary alloy nanoparticles have been fabricated by electron-beam evaporation followed by postdeposition annealing. A single L1(0) phase was formed in the FeCuPd nanoparticles with (Fe+Cu) content lower than 48 at. %. A strong preferential c-axis orientation along the film normal direction was achieved by Cu addition, which leads to a strong perpendicular magnetic anisotropy. Also, a lowering of the ordering temperature by 50 K compared to the binary L1(0)-FePd nanoparticles was achieved by Cu addition. By contrast, composite particles composed of the bcc Fe and the L1(0)-FeCuPd were formed when the (Fe+Cu) content was higher than 52 at. %. Coexistence of the bcc Fe and the L1(0)-FeCuPd was confirmed by high-resolution transmission electron microscopy and nanobeam electron diffraction. It was found that perpendicular magnetic anisotropy of the L1(0)-FeCuPd nanoparticles on the NaCl substrate is sensitive to the alloy composition. (C) 2006 American Institute of Physics.

  247. Structure and magnetic properties of iron nitride films prepared by reactive dc magnetron sputtering 査読有り

    H Naganuma, R Nakatani, Y Endo, Y Kawamura, M Yamamoto

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (7A) 4166-4170 2004年7月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.43.4166  

    ISSN:0021-4922

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    We have investigated the structure and magnetic properties of iron nitride films prepared by reactive dc magnetron sputtering with an argon gas flow rate of 12 sccm and a nitrogen gas flow rate varied between 0-10sccm. Under the above conditions, the nitrogen concentrations in the iron nitride films were changed from 0 to 33 at.%. The phase and structure of the films changed from alpha-Fe, amorphous matrix with nanocrystallites of epsilon-Fe3N epsilon-FexN (2 &lt; x less than or equal to 3) to zeta-Fe2N phase as the nitrogen concentration of the iron nitride films increases, and these changes in the phase almost correspond to the Fe-N phase diagram. The saturation magnetization of the iron nitride films decreases as the nitrogen concentration increases up to 31 at.%, and disappears at 33 at.%. A relatively low coercivity of 9 Oe is observed at the nitrogen concentrations from I I to 18 at.%. From the results of structural analysis and magnetic measurements, it is confirmed that the coercivity of the iron nitride films mostly correlates with the changes in grain size.

  248. Magnetic properties of weak itinerant ferromagnetic xi-Fe2N film 査読有り

    H Naganuma, Y Endo, R Nakatani, Y Kawamura, M Yamamoto

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 5 (1-2) 83-87 2004年1月

    出版者・発行元:NATL INST MATERIALS SCIENCE

    DOI: 10.1016/j.stam.2003.10.008  

    ISSN:1468-6996

    詳細を見る 詳細を閉じる

    We have studied magnetic properties of xi-Fe2N film deposited onto surface-oxidized Si(100) substrates by reactive dc magnetron sputtering with an argon-nitrogen atmosphere. At the temperature less than 120 K, the magnetic moment of the 120 nm-thick xi-Fe2N film is hard to be saturated at magnetic fields up to 50 kOe, and the magnetic moment is weak. The inverse susceptibility linearly increases as the temperature increases between 65 and 160 K, and the change of the inverse susceptibility obeys the Curie-Weiss law. From the results of magnetization measurements, the magnetic parameter of the Curie temperature, the spontaneous magnetic moment at 0 K and the effective magnetic moment can be estimated to be 35 +/- 2.5 K, 0.028 mu(B)/iron atom and 0.70 mu(B)/iron atom, respectively. These parameters suggest that the xi-Fe2N film is in the weak itinerant electron ferromagnetic state. These parameters can be also explained by self-consistently renormalization (SCR) theory. (C) 2003 Elsevier Ltd. All rights reserved.

  249. Magnetic and electrical properties of iron nitride films containing both amorphous matrices and nanocrystalline grains 査読有り

    H Naganuma, R Nakatani, Y Endo, Y Kawamura, M Yamamoto

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 5 (1-2) 101-106 2004年1月

    出版者・発行元:NATL INST MATERIALS SCIENCE

    DOI: 10.1016/j.stam.2003.10.020  

    ISSN:1468-6996

    詳細を見る 詳細を閉じる

    We have investigated the magnetic and electrical properties of iron nitride films containing both amorphous matrices and nanocrystalline grains. It is found that both the number and the size of the grains in the amorphous matrix increase as the film thickness increases. The grain is confirmed to have an epsilon-Fe3N structure and the grain size varies in the range of 10-300 nm. The saturation magnetization and the coercivity increase as the number and the size of the grains increase. The electrical resistivity of the iron nitride films is higher than that of the iron film. It is considered that the amorphous matrices cause the high resistivity in the iron nitride films. (C) 2003 Elsevier Ltd. All rights reserved.

  250. Preparation of CoFe2O4 spin valves and improvement of their magnetoresistance property by postannealing 査読有り

    H Naganuma, S Okamura, H Sakakima, T Shiosaki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 (11) 6865-6868 2003年11月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.42.6865  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    We have fabricated spin valves which had the simple structure Of Si/SiO2/CoFe2O4 (40 nm)/Co (2 nm)/Cu (2 nm)/Co (4 nm) by rf-magnetron sputtering at room temperature. A hard magnetic and insulating Co-ferrite film was used as a pinning layer. As-deposited films showed a high sheet resistance of 36.3 Omega/square and a magnetoresistance (MR) ratio of 4.5%. The MR property of the spin valves was significantly improved by postannealing in a vacuum. An MR ratio of 10.5% was attained by annealing at 300degreesC for 4 h. The variation in sheet resistance was approximately 3.9 Omega/square. This remarkable increase in MR ratio could be attributed to the construction of clear Co/Cu/Co/CoFe2O4 interfaces and the improvement of the magnetic property of the Co-ferrite layer by postannealing.

︎全件表示 ︎最初の5件までを表示

MISC 25

  1. 走査透過型電子顕微鏡を用いた高L1<sub>0</sub>規則度を有するFePdエピタキシャル膜の極微構造観察

    西嶋雅彦, 永沼博, 永沼博, 永沼博, 永沼博

    応用物理学会春季学術講演会講演予稿集(CD-ROM) 68th 2021年

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    永沼博, 一ノ瀬智浩, ZHAO H. J., INIGUEZ J., 安井伸太郎, BAE In-Tae

    応用物理学会東北支部学術講演会(CD-ROM) 75th 2020年

  3. [Foreword] Manipulation of multi-degrees of freedom in ferroic-ordering

    Hiroshi Naganuma, Hironori Fujisawa, Takashi Iijima

    Japanese Journal of Applied Physics 57 090201-090201 2018年6月

  4. 傾斜組成Bi<sub>1-x</sub>Sm<sub>x</sub>FeO<sub>3</sub>薄膜の分極反転挙動

    穴田柚冬, 丸山伸伍, 安井伸太郎, 永沼博, 伊藤満, 松本祐司

    応用物理学会秋季学術講演会講演予稿集(CD-ROM) 79th 2018年

    ISSN:2758-4704

  5. 高垂直磁気異方性L10規則合金を用いたスピンダイナミクス

    永沼 博

    まてりあ 54 (8) 383-389 2015年8月1日

    出版者・発行元:日本金属学会

    DOI: 10.2320/materia.54.383  

    ISSN:1340-2625

  6. 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

  7. Temperature Dependence of Low Frequency Noise in Magnetic Tunneling Junctions with Co40Fe40B20/Co70.5Fe4.5Si15B10 Composed Free Layer.

    Z. Yuan, J. Feng, P. Guo, T. Nakano, S. Ali, X. Han, H. Naganuma, Y. Ando

    2015 IEEE MAGNETICS CONFERENCE (INTERMAG) 2015年

    出版者・発行元:IEEE

  8. 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

  9. Bulk Electronic Structure of BiFe1-xMxO3 (M=Mn and Co) Thin Films by Soft-X-Ray Spectroscopy

    T. Higuchi, H. Naganuma, J. Miura, Y. Inoue, S. Okamura

    Activity Report 2011 of SRL-ISSP 9-10 2012年10月

  10. 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

  11. 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

  12. 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

  13. 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

  14. MOCVD法で作製したエピタキシャルBiFeO<sub>3</sub>-BiCoO<sub>3</sub>膜の結晶相と電気特性

    安井伸太郎, 永沼博, 岡村総一郎, 西田謙, 山本孝, 飯島高志, 東正樹, 森岡仁, 森岡仁, 斎藤啓介, 舟窪浩

    応用物理学関係連合講演会講演予稿集 55th (2) 2008年

  15. Co-BiFeO<sub>3</sub>薄膜における抗電界の低減および自発磁化の発現

    永沼博, 三浦淳, 志村希, 安井伸太郎, 西田謙, 飯島高志, 舟窪浩, 岡村総一郎

    応用物理学関係連合講演会講演予稿集 55th (2) 2008年

  16. 偏光ラマン分光法を用いた分極軸単一配向した正方晶PZT厚膜の評価

    中島光雅, 藤沢隆志, 加茂嵩史, 安井伸太郎, 長田実, 西田謙, 山本孝, 河東田隆, 永沼博, 岡村総一郎, 舟窪浩

    応用物理学関係連合講演会講演予稿集 55th (2) 2008年

  17. MOCVD法によるBiFeO<sub>3</sub>-BiCoO<sub>3</sub>膜の作製と特性評価

    安井伸太郎, 舟窪浩, 永沼博, 岡村総一郎, 西田謙, 山本孝, 飯島高志, 森岡仁, 斎藤啓介

    セラミックス基礎科学討論会講演要旨集 46th 2008年

  18. BiFeO<sub>3</sub>-BiCoO<sub>3</sub>固溶体薄膜の磁気特性および強誘電性

    永沼博, 安井伸太郎, 西田謙, 飯島高志, 舟窪浩, 岡村総一郎, 安藤康夫

    応用物理学会学術講演会講演予稿集 69th (2) 2008年

  19. MPBを有するBiFcO<sub>3</sub>-BiCoO<sub>3</sub>エピタキシャル薄膜の磁性と強誘電性

    永沼博, 安井伸太郎, 西田謙, 舟窪浩, 飯島高志, 安藤康夫, 岡村総一郎

    日本磁気学会学術講演概要集 32nd 2008年

    ISSN:1882-2959

  20. エピタキシャル膜を用いた新規圧電体探索方法の提案

    舟窪 浩, 森岡 仁, 斉藤 啓介, 内田 寛, 安井 伸太郎, 中島 光雅, 永沼 博, 岡村 総一郎, 西田 謙, 山本 孝, 飯島 高志, 東 正樹

    日本セラミックス協会 年会・秋季シンポジウム 講演予稿集 2008 (0) 431-431 2008年

    出版者・発行元:公益社団法人 日本セラミックス協会

    DOI: 10.14853/pcersj.2008F.0.431.0  

    詳細を見る 詳細を閉じる

    非鉛圧電体の探索、特にMPB探索は電子セラミックスの急務な課題である。これまでの研究で探索できなかった新材料を探索する方法として、我々はエピタキシャル薄膜を用いた探索方法を提案する。この方法は従来の焼結体を用いる方法と比較して、_丸1_高圧相のような従来まったく検討されていない組成系を探索できる、_丸2_焼結密度に左右されないで評価できる、_丸3_大きな電界を印加した評価が容易である、_丸4_結晶方位依存性の探索が容易できるといった利点がある。反面、_丸1_基板からの拘束による構成相の変化といった懸念点がある。本発表ではれらに関して、実例を照会しながら紹介する。

  21. 圧電応用を目指した一軸配向Biペロブスカイト酸化物厚膜のMOCVD法作製とその特性評価

    安井伸太郎, 永沼博, 岡村総一郎, 飯島高志, 西田謙, 舟窪浩

    応用物理学関係連合講演会講演予稿集 54th (2) 2007年

  22. Bi(CO<sub>x</sub>Fe<sub>1-x</sub>)O<sub>3</sub>薄膜の構造,強誘電性および磁気特性

    三浦淳, 永沼博, 志村希, 島宏美, 安井伸太郎, 西田謙, 河東田隆, 舟窪浩, 飯島高志, 岡村総一郎

    日本応用磁気学会学術講演概要集 31st 2007年

    ISSN:1340-8100

  23. Bi(Fe<sub>x</sub>,Co<sub>1-x</sub>)O<sub>3</sub>薄膜の強誘電性

    志村 希, 永沼 博, 島 宏美, 安井 伸太郎, 西田 謙, 飯島 高志, 舟窪 浩, 岡村 総一郎

    日本セラミックス協会 年会・秋季シンポジウム 講演予稿集 2007 (0) 304-304 2007年

    出版者・発行元:公益社団法人 日本セラミックス協会

    DOI: 10.14853/pcersj.2007S.0.304.0  

    詳細を見る 詳細を閉じる

    環境への配慮から鉛の使用が規制されはじめたため鉛に代替する新規非鉛圧電物質の探索が必要となってきた。本研究では高い残留分極値を有するBiFeO&lt;SUB&gt;3&lt;/SUB&gt;、および高い正方晶歪みを有するBiCoO&lt;SUB&gt;3&lt;/SUB&gt;を選択し、BiFeO&lt;SUB&gt;3&lt;/SUB&gt;-BiCoO&lt;SUB&gt;3&lt;/SUB&gt;系におけるMPB探索を行なった。X線構造解析の結果、Fe組成比が0.9では主にBiFeO&lt;SUB&gt;3&lt;/SUB&gt;相に起因した回折ピークが観測されるが、Fe組成比が0.8のときBiFeO&lt;SUB&gt;3&lt;/SUB&gt;相に起因した回折ピークは消失して結晶構造が急激に変化していることがわかった。PUND測定(@80K)の結果、Fe組成比が0.8-1.0まで比較的高い残留分極を示すが、Fe組成比が0.7のとき残留分極は急激に低下した。このことから結晶構造が変化し、かつ強誘電性を示したFe組成比が0.8-0.9の間にMPBが存在している可能性が示唆された。

  24. Fe_xN単層膜および多層膜の構造と磁性

    永沼 博, 遠藤 恭, 山本 雅彦

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 26 284-284 2002年9月1日

    ISSN:1340-8100

  25. CoFe_2O_4系スピンバルブ膜のMR特性およびそのアニール温度依存性

    永沼 博, 岡村 総一郎, 塩嵜 忠

    日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 24 417-417 2000年9月1日

    ISSN:1340-8100

︎全件表示 ︎最初の5件までを表示

書籍等出版物 6

  1. L10-FePd/グラフェン界面のChemisorption 型ファン デルワールス結合による堅牢な界面垂直磁気異方性の 発現

    永沼 博

    放射光 2022年12月

    詳細を見る 詳細を閉じる

    六方晶系グラフェンをトンネル障壁層,正方晶系L10-FePd 合金を垂直磁化記録層とした異種結晶界面を有する強 磁性トンネル接合素子を次世代のシングルナノメーター世代の高記録密度の不揮発性磁気メモリへの応用に向け て,本研究では,L10-FePd/グラフェン異種界面を作製し,界面構造および界面磁気特性について評価した。L10- FePd 層はr.f. スパッタリング法によりSrTiO3 基板上にエピタキシャル成長させ,グラフェン層は化学気相成長 (Chemical vapor deposition: CVD)法によりL10-FePd 上に成長させた。L10-FePd/グラフェン異種界面の界面磁 性を,高エネルギー加速器研究機構フォトンファクトリBL-16において,深さ分解X 線磁気円二色性(X-ray magnetic circular dichroism: XMCD)により評価した。深さ分解XMCD 測定から,L10-FePd のFe は垂直方向に強 い界面軌道磁気モーメントを発現していることがわかった。L10-FePd/グラフェン異種結晶界面の界面原子構造を 断面走査透過電子顕微鏡(Scanning Transmission Electron Microscope: STEM)観察により調べた。断面 STEM 観察像から,グラフェンとL10-FePd 層間距離は0.2 nm であり,グラファイトの層間距離(0.38 nm)に比 べて短縮されていた。この層間距離の短縮により,界面の電子密度が増大し,強い混成軌道を有するChemisorption 型のファンデルワールス力となり,L10-FePd/グラフェンに界面垂直磁気異方性が誘起されたと考えられる。 界面垂直磁気異方性とL10-FePd の一軸の強い結晶磁気異方性の相乗効果は,記録情報の保持特性を向上させる。 さらに,グラフェンの垂直方向の低抵抗トンネル伝導はCMOS の負荷を低減させる。このような諸物性は,超高記 録密度の不揮発性磁気メモリの構成材料としてL10-FePd/グラフェンが期待できることを示唆している。

  2. 強磁性トンネル接合素子の強磁性電極材料

    永沼 博

    電子情報通信学会 2022年12月1日

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    電子の電荷だけでなくスピンの自由度を利用した強磁性トンネル接合素子は,基礎物性の理解が深まり,回路システム と統合させたデバイスを目指す段階となっている.強磁性トンネル接合素子は極薄の絶縁層を2 枚の強磁性電極層で挟ん だ3 層が基本構造となる.強磁性電極の磁気特性により,超高感度磁気センサ,不揮発性磁気メモリ素子,及びスピン発 振・検波素子,等になり得る.本稿では,強磁性トンネル接合の強磁性電極材料に応じたデバイス例を幾つか紹介しなが ら概説する.

  3. 室温以上に転移温度のある界面マルチフェロイックス-高感度磁気センサへの応用に向けて-

    永沼 博

    セラミックス 2021年7月

  4. ペロブスカイトエピタキシャル膜の構造解析と界面キャリア注入効果

    永沼 博

    東京工業大学フロンティア材料研究所 2020年10月

  5. Materials Science Advanced Topics 'Optical properties on multiferroic BiFeO3 films'

    Hiromi Shima, Hiroshi Naganuma, Soichiro Okamura

    2013年6月1日

  6. FERROELECTRICS Physical effects 'Magnetoelectrics and Multiferroics' Chapter 16

    Hiroshi Naganuma

    2011年7月

︎全件表示 ︎最初の5件までを表示

講演・口頭発表等 89

  1. Cr, Mn, Co, Ni, Cu添加BiFeO3薄膜の膜構造、強誘電性および磁気特性

    永沼 博, 岡村 総一郎, 安藤 康夫

    特定領域「スピン流の創出と制御」研究会 2008年7月23日

  2. Analysis for Crystal Structure and Electric Properites of Epitaxial BiFeO3-BiCoO3 Films Grown by MOCVD 国際会議

    Sintaro Yasui, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Takashi Iijima, Masaaki Azuma, Hitoshi Morioka, Keisuke Saito, Hiroshi Funakubo

    International Symposium on Integrated Feroelectrics 2008年6月12日

  3. BiFeO3-BiCoO3固溶体薄膜におけるMPB-ME効果の可能性について

    永沼 博, 安井 伸太郎, 舟窪 浩, 西田 謙, 飯島 高志, 安藤 康夫, 岡村 総一郎

    特定領域研究会 第二回トピカルミーティング 2008年6月7日

  4. Co添加によるBiFeO3薄膜の自発磁化の発現および抗電界の低減

    永沼 博, 三浦 淳, 岡村 総一郎, 安井 伸太郎, 舟窪 浩, 西田 謙, 飯島 高志, 飯島 高志, 東 正樹, 神島 謙二, 柿崎 浩一, 平塚 信之

    第25回強誘電体応用会議 2008年5月30日

  5. (Pb,La)(Zr1-x,Tix)O3 (x=0.1-0.9)膜の電気光学特性及び圧電特性

    島 宏美, 飯島 高志, 舟窪 浩, 永沼 博, 岡村 総一郎

    第25回強誘電体応用会議 2008年5月30日

  6. MOCVD法によるエピタキシャルBiFeO3-BiCoO3膜の作製とその結晶構造の膜厚依存性

    安井 伸太郎, 永沼 博, 岡村 総一郎, 西田 謙, 山本 孝, 飯島 高志, 東 正樹, 森岡 仁, 斎藤 啓介, 舟窪 浩

    第25回強誘電体応用会議 2008年5月29日

  7. Increment of saturation magnetization and reduction of electric coercive field in multiferroic Bi ferrite films by adding cobalt 国際会議

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    IEEE International Magnetics Conference 2008年5月7日

  8. BiFeO3多結晶薄膜の極微構造、強誘電性および磁性

    永沼 博, 井上 洋介, Kovacs Andras, 弘津 禎彦, Balogh Judit, 岡村 総一郎

    応用物理学会 2008年3月30日

  9. MOCVD法で作製したエピタキシャルBiFeO3-BiCoO3膜の結晶相と電気特性

    安井 伸太郎, 永沼 博, 岡村 総一郎, 西田 謙, 山本 孝, 飯島 高志, 東 正樹, 森岡 仁, 斎藤 啓介, 舟窪 浩

    応用物理学会 2008年3月30日

  10. Co-BiFeO3薄膜における抗電界の低減および自発磁化の発現

    永沼 博, 三浦 淳, 志村 希, 安井 伸太郎, 西田 謙, 飯島 高志, 舟窪 浩, 岡村 総一郎

    応用物理学会 2008年3月30日

  11. (001), (110), (111)SrTiO3単結晶基板上にエピタキシャル成長させたBiFeO3薄膜の評価

    曽根 圭太, 永沼 博, 岡村 総一郎

    応用物理学会 2008年3月30日

  12. 界面/強誘電両層での電荷移動を考慮したPZT薄膜キャパシタのインプリント進行モデル

    小鹿 聡一郎, 島 宏美, 永沼 博, 岡村 総一郎

    応用物理学会 2008年3月29日

  13. (Pb,La)(Zr,Ti)O3多結晶膜における光学特性のZr/Ti比依存性

    島 宏美, 飯島 高志, 舟窪 浩, 永沼 博, 岡村 総一郎

    応用物理学会 2008年3月29日

  14. 強誘電体Pb(Zr,Ti)O3薄膜キャパシタのリーク電流特性に対する測定条件の影響

    岡村 総一郎, 谷村 光応, 島 宏美, 永沼 博

    応用物理学会 2008年3月29日

  15. 偏光ラマン分光法を用いた分極軸単一配向した正方晶PZT厚膜の評価

    中島 光雅, 藤澤 隆志, 加茂 嵩史, 安井 伸太郎, 長田 実, 西田 謙, 山本 孝, 河東田 隆, 永沼 博, 岡村 総一郎, 舟窪 浩

    応用物理学会 2008年3月29日

  16. MOCVD法によるBiFeO3-BiCoO3膜の作製と特性評価

    安井 伸太郎, 舟窪 浩, 永沼 博, 岡村 総一郎, 西田 謙, 山本 孝, 飯島 高志, 森岡 仁, 斎藤 啓介

    セラミックス基礎科学討論会 2008年1月11日

  17. Evaluation of Leakage Current Density and Remanent Polarization by PUND Measurements in Co Added Multiferroic BiFeO3 films

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    The 18th Symposium of The Materials Research of Society of Japan 2007年12月9日

  18. Estimation of an Activation Energy for Poole-Frenkel Conduction in Ferroelectric PZT Thin-film Capacitors

    Mitsumasa Tanimura, Hiromi Shima, Hiroshi Naganuma, Soichiro Okamura

    The 18th Symposium of The Materials Research of Society of Japan 2007年12月9日

  19. Vaporization Characteristics of Solid Titanium Sources for Metalorganic Chemical Vapor Deposition

    Ryusuke Furuya, Ayako Inoue, Hiroshi Naganuma, Soichiro Okamura

    The 18th Symposium of The Materials Research of Society of Japan 2007年12月9日

  20. Growth behavior of TiO2 Films by MOCVD using three kinds of titanium precursors

    Ayako Inoue, Ryusuke Fruya, Tsutomu Ochiai, Hiroshi Naganuma, Soichiro Okamura

    The 18th Symposium of The Materials Research of Society of Japan 2007年12月9日

  21. Bi系マルチフェロイック薄膜の強誘電性および磁性 -ME効果の発現に向けて-

    永沼 博, 岡村 総一郎, 神島 謙二, 柿崎 浩一, 平塚 信之, dras Kovacs, 平田 秋彦, 弘津 禎彦

    日本応用磁気学会、ナノマグネティクス研究会 2007年11月30日

  22. Effect of 3d transition metals addition on the ferroelectric and magnetic properties in Bi ferrite thin films 国際会議

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    Material Research Society 2007年11月26日

  23. PUND measurements for the BiFeO3 films –Temperature dependence of the ferroelectricity– 国際会議

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    Material Research Society 2007年11月26日

  24. Enhancement of ferroelectric and magnetic properties in BiFeO3 films by small amount of cobalt addition 国際会議

    Hiroshi Naganuma, Nozomi Shimura, Jun Miura, Hiromi Shima, Shintaro Yasui, Ken Nishida, Takashi Katoda, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    52th Magnetism and Magnetic Materials Conference 2007年11月9日

  25. 駆動パルスの連続印加がPZT厚膜の圧電特性に及ぼす影響

    小林 裕二, 永沼 博, 岡村 総一郎, 飯島 高志

    日本セラミックス協会 2007年9月12日

  26. BiMnO3 エピタキシャル薄膜の作製および磁気特性

    波利摩 徹朗, 永沼 博, 島 宏美, 岡村 総一郎

    日本応用磁気学会 2007年9月11日

  27. Bi(CoxFe1-x)O3 薄膜の構造,強誘電性および磁気特性

    三浦 淳, 永沼 博, 志村 希, 島 宏美, 安井 伸太郎, 西田 謙, 河東田 隆, 舟窪 浩, 飯島 高志, 岡村 総一郎

    日本応用磁気学会 2007年9月11日

  28. Bi-Fe-Ox コンポジット薄膜の構造,磁性および強誘電性

    大久保 智聡, 永沼 博, 神島 謙二, 柿崎 浩一, 平塚 信之, 岡村 総一郎

    日本応用磁気学会 2007年9月11日

  29. マルチフェロイック材料の構造および物性

    永島 義崇, 神島 謙二, 柿崎 浩一, 平塚 信之, 永沼 博, 岡村 総一郎

    日本応用磁気学会 2007年9月11日

  30. マルチフェロイックBiFeO3 を母体としたコンポジット薄膜の構造および磁気特性

    大久保 智聡, 永沼 博, 岡村 総一郎

    応用物理学会 2007年9月7日

  31. PZT薄膜キャパシタのインプリント特性の分極方向依存性ならびに膜厚依存性

    小鹿 聡一郎, 島 宏美, 永沼 博, 岡村 総一郎

    応用物理学会 2007年9月6日

  32. 強誘電体Pb(Zr,Ti)O3薄膜キャパシタのリーク電流の温度依存性と物性値の推定

    岡村 総一郎, 谷村 光応, 島 宏美, 小鹿 聡一郎, 永沼 博

    応用物理学会 2007年9月6日

  33. Cr, Mn, Co, Ni, Cu添加BiFeO3薄膜のリーク電流特性および強誘電性

    三浦 淳, 大久保 智聡, 永沼 博, 岡村 総一郎

    応用物理学会 2007年9月5日

  34. BiFeO3薄膜の強誘電性および磁性の本焼成温度依存性

    井上 洋介, 永沼 博, 岡村 総一郎

    応用物理学会 2007年9月5日

  35. 低温PUND測定によるBiFeO3多結晶薄膜の自発分極量に関する考察

    永沼 博, 井上 洋介, 岡村 総一郎

    応用物理学会 2007年9月5日

  36. Electric properties of polycrystalline BaPbO3 films on annealing 国際会議

    Hiroshi Naganuma, Kayoko Yamada, Hiromi Shima, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    International Conference on Electroceramics 2007年8月1日

  37. Effect of annealing temperature on ferroelectric and magnetic properties in Mn-doped BiFeO3 films 国際会議

    Hiroshi Naganuma, Jun Miura, Soichiro Okamura

    International Conference on Electroceramics 2007年8月1日

  38. Fabrication of Oriented Hard-Magnetic Alloy Nonoparticles and Their Characterization 国際会議

    Yoshihiko Hirotsu, Kazuhisa Sato, Andras Kovacs, Hiroshi Naganuma, Han W-Ryu

    International Symposium on Advanced Magnetic Materials and Applications 2007年5月30日

  39. Influence of Pb and La Contents on the Lattice Configuration of La-substituted Pb(Zr0.65,Ti0.35)O3 Films 国際会議

    Hiromi Shima, Ken Nishida, Hiroshi Funakubo, Tadashi Iijima, Takashi Katoda, Hiroshi Naganuma, Soichiro Okamura

    International Symposium on the Application of Ferroelectrics 2007年5月29日

  40. Preparation and characterization of Bi-perovskite oxide films for piezo applications 国際会議

    Shintaro Yasui, Hiroshi Naganuma, Soichiro Okamura, Takashi Iijima, Ken Nishida, Hiroshi Uchida, Seiichiro Koda, Hiroshi Funakubo

    International Symposium on the Application of Ferroelectric 2007年5月29日

  41. Leakage Current Property of Pb(Zr0.4,Ti0.6)O3 Thin-film Capacitors with Highly Rectangular Hysteresis Property 国際会議

    Soichiro Okamura, Mitsuhiro Tanimura, Hiromi Shima, Hiroshi Naganuma

    International Symposium on the Application of Ferroelectrics 2007年5月29日

  42. Structural and ferroelectric properties of BiFeO3-BiCoO3 solid solution films 国際会議

    Hiroshi Naganuma, Nozomi Shimura, Hiromi Shima, Shintaro Yasui, Ken Nishida, Tadashi Ijima, Hiroshi Funakubo, Soichiro Okamur

    International Symposium on the Application of Ferroelectrics 2007年5月28日

  43. Temperature dependence of ferroelectric and magnetic properties in polycrystalline BiFeO3 films 国際会議

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    International Symposium on the Application of Ferroelectrics 2007年5月28日

  44. Ferroelectric and magnetic properties of multiferroic FeOx-BiFeO3 composite film 国際会議

    Hiroshi Naganuma, Tomosato Okubo, Soichiro Okamura

    International Symposium on the Application of Ferroelectrics 2007年5月28日

  45. 分極反転の繰り返しがPZT厚膜の圧電特性及び強誘電特性に及ぼす影響

    小林 裕二, 永沼 博, 岡村 総一郎, 飯島 高志

    強誘電体応用会議 2007年5月25日

  46. Effect of Piezoelectric Displacement on Electrooptic Property of Polycrystalline (Pb,La)(Zr,Ti)O3 Film 国際会議

    Hiromi Shima, Hiroshi Naganuma, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    International Symposium on Integrated Ferroelectrics 2007年5月10日

  47. Bi concentration dependence of ferroelectric and magnetic properties in BiFeO3 films 国際会議

    Hiroshi Naganuma, Tomosato Okubo, Soichiro Okamura

    International Symposium on Integrated Ferroelectric 2007年5月10日

  48. Leakage current mechanism of BiFeO3 films 国際会議

    Hiroshi Naganuma, Yosuke Inoue, Soichiro Okamura

    International Symposium on Integrated Ferroelectric 2007年5月10日

  49. Imprint Behavior Of Ferroelectric PZT Thin-Film Capacitors In The Early Stage 国際会議

    Soichiro Koshika, Hiromi Shima, Hiroshi Naganuma, Soichiro Okamura

    International Symposium on Integrated Ferroelectric 2007年5月9日

  50. 界面層の伝導機構変化を取り入れたインプリントの進行モデル

    小鹿 総一郎, 島 宏美, 永沼 博, 岡村 総一郎

    応用物理学会 2007年3月29日

  51. 圧電応答を目指した一軸配向Biペロブスカイと酸化物厚膜のMOCVD法作製とその特性評価

    安井伸 太郎, 永沼 博, 岡村 総一郎, 飯島 高志, 西田 謙, 舟窪 浩

    応用物理学会 2007年3月28日

  52. マルチフェロイックBiFeO3薄膜の透過型電子顕微鏡による極微構造観察

    永沼 博, 岡村 総一郎, dras Kovacs, 平田 秋彦, 弘津 禎彦

    日本金属学会 2007年3月28日

  53. Cr、Mn、Co、Ni、Cu添加BiFeO3薄膜の構造および磁気特性

    三浦 淳, 永沼 博, 神島 謙二, 柿崎 浩一, 平塚 信之, 岡村 総一郎

    応用物理学会 2007年3月27日

  54. 化学溶液堆積法によりSrTiO3(100)基板上に作製したBiMnO3薄膜の構造および強誘電特性および磁性

    波利摩 徹朗, 永沼 博, 島 宏美, 岡村 総一郎

    応用物理学会 2007年3月27日

  55. BiFeO3薄膜の構造、強誘電性および磁気特性のBiおよびFe組成依存性

    大久保 智聡, 永沼 博, 岡村 総一郎

    応用物理学会 2007年3月27日

  56. 100 kHz駆動による室温におけるマルチフェロイックBiFeO3薄膜のヒステリシス測定

    永沼 博, 井上 洋介, 岡村 総一郎

    応用物理学会 2007年3月27日

  57. BiFeO3薄膜のリーク電流特性

    井上 洋介, 永沼 博, 岡村 総一郎

    応用物理学会 2007年3月27日

  58. マルチフェロイックBiFeO3薄膜の極微構造、強誘電性および磁性

    永沼 博, 岡村 総一郎

    応用物理学会 2007年3月27日

  59. FeOx混在BiFeO薄膜の磁気特性および強誘電特性

    永沼 博, 大久保 智聡, 岡村 総一郎

    日本金属学会 2007年3月27日

  60. La置換Pb(Zr,Ti)O3膜の電気光学特性とLa置換サイト

    島 宏美, 西田 謙, 舟窪 浩, 飯島 高志, 河東田 隆, 永沼 博, 岡村 総一郎

    日本セラミックス協会 2007年3月22日

  61. BaTiO3-BiCoO3薄膜の構造、強誘電特性および磁気特性

    高岩 徳寿, 永沼 博, 島 宏美, 飯島 高志, 舟窪 浩, 岡村 総一郎

    日本セラミックス協会 2007年3月22日

  62. Bi(FexCo1-x)O3薄膜の強誘電性

    志村 希, 永沼 博, 島 宏美, 飯島 高志, 安井 伸太郎, 舟窪 浩, 岡村 総一郎

    日本セラミックス協会 2007年3月22日

  63. Structural, magnetic and ferroelectric properties of multiferroic BiFeO3 film fabricated by chemical solution deposition 国際会議

    Hiroshi Naganuma, Soichiro Okamura

    Joint MMM/Intermag Conference 2007年1月11日

  64. La Content Dependence of Piezoelectric Properties of Polycrystalline (Pb,La)(Zr0.65,Ti0.35)O3 Film

    Hiromi Shima, Hiroshi Naganuma, Takashi Iijima, Hiroshi Funakubo, Soichiro Okamura

    MRS-J 2006年12月10日

  65. Preparation and Characterization of Multiferroic BiFeO3 films

    Hiroshi Naganuma, Yosuke Inoue, Andras Kovacs, Yirotsu Hirotsu, Soichiro Okamura

    MRS-J 2006年12月10日

  66. Low temperature synthesis of high-density FePtCu nanooparticles fabricated by rf-magnetron sputtering 国際会議

    Han W-Ryu, Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    The 16th International Microscopy Congress 2006年9月8日

  67. Characterization of 2D-dispersed FeCuPd alloy nanoparticles 国際会議

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    The 16th International Microscopy Congress 2006年9月8日

  68. Systematic Fabrication of (Ba,Sr)TiO3 Microdots with Various Ba/Sr Ratios by Ink-jet Printing and their Evaluation 国際会議

    Soichiro Okamura, Hiromi Shima, Hiroshi Naganuma, Jyunji Musha, Tadashi Shiosaki

    The 5th Asian meeting on Ferroelectrics 2006年9月6日

  69. Optimization of Pd content in a Precursor Solution for the Fabrication of (Pb,Ls)(Zr,Ti)O3 Films for Optical Applications by Chemical Solution Deposition 国際会議

    Hiromi Shima, Hiroshi Naganuma, Yukihiko Ishii, Soichiro Okamura, Akira Takashima

    The 5th Asian meeting on Ferroelectrics 2006年9月6日

  70. (Pb,La)(Zr0.65,Ti0.35)O3多結晶膜における電気光学特性のLa量・配向依存性

    島 宏美, 永沼 博, 岡村 総一郎

    応用物理学会 2006年8月31日

  71. Particle size dependence of atomic ordering and magnetic properties of L10-FePd nanoparticles 国際会議

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    International Conference on Magnetism 2006年8月24日

  72. L10型FePdナノ粒子の規則構造と磁気的性質の粒径依存性

    永沼 博, 佐藤 和久, 弘津 禎彦

    日本金属学会 2006年3月23日

  73. Effect of Cu addition on structural and magnetic properties of isolated L10-FeCuPd nanoparticles

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    The 9th Sanken International Symposium 2006 on Advanced Science and Technology for Materials, Biology, and Information by Quantum Beams 2006年2月8日

  74. Perpendicular magnetic anisotropy of L10-FeCuPd nanoparticles induced by Cu addition 国際会議

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    MRS 2005年11月30日

  75. Fabrication of oriented L10-FeCuPd and bcc-Fe/L10-FeCuPd nanocomposite isolated particles: alloy composition dependence of magnetic properties 国際会議

    Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    50th Magnetism and Magnetic Materials Conference 2005年11月2日

  76. Low temperature ordering of high-density FePtCu nanoparticles fabricated by rf-magnetron sputtering 国際会議

    Han Wool Ryu, Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotus

    2nd Asian Forum in Korea 2005年10月

  77. L10型FePdCuナノ粒子の構造形態と磁気特性の組成依存性

    永沼 博, 佐藤 和久, 弘津 禎彦

    日本金属学会 2005年9月29日

  78. c軸垂直配向FePdCu規則合金ナノ粒子の極微構造および磁気特性

    永沼 博, 佐藤 和久, 弘津禎彦

    日本応用磁気学会 2005年9月22日

  79. Structure and Magnetic Properties of Oriented Fe-Pt(-Cu) Nanoparticles

    Han W-Ryu, Takashi Kotera, Hiroshi Naganuma, Kazuhisa Sato, Yoshihiko Hirotsu

    日本金属学会 2005年3月31日

  80. Cu添加Fe-Pdナノ粒子の構造と磁気特性

    永沼 博, 小寺 貴士, 佐藤 和久, 弘津 禎彦

    日本金属学会 2005年3月31日

  81. Improvement on Hard Magnetic Property of L10-FePd Nanoparticles by Cu Addition

    Hiroshi Naganuma, Tadashi Kotera, Kazuhisa Sato, Yoshihiko Hirotsu

    owards Creation New Industries Based on Inter-Nanoscience Third International Symposium 2005年3月9日

  82. 窒素ガス反応性スパッタリングにより作製したFe-N薄膜の構造と磁性

    永沼 博, 遠藤 恭, 中谷 亮一, 川村 良雄, 山本 雅彦

    日本金属学会 2003年3月29日

  83. 窒化鉄の熱分解挙動とその磁気特性

    小林 秀彦, 永沼 博, 山崎 武, 柿崎 浩一, 平塚 信之

    日本セラミックス協会 2003年3月

  84. FexN単相膜および多層膜の構造と磁性

    永沼 博, 遠藤 恭, 山本 雅彦

    日本応用磁気学会 2002年9月19日

  85. 窒化鉄薄膜および多層膜の作製と磁気特性

    永沼 博, 遠藤 恭, 山本 雅彦

    日本金属学会 2002年3月28日

  86. CoFe2O4系スピンバルブ膜のMR特性およびそのアニール温度依存性

    永沼 博, 岡村 総一郎, 塩嵜 忠

    日本応用磁気学会 2000年9月15日

  87. Pt下地膜上に成膜した結晶性CoFe2O4系スピンバルブ膜に関する研究

    永沼 博, 岡村 総一郎, 塩嵜 忠

    応用物理学会 2000年9月3日

  88. 室温製膜したCoFe2O4系スピンバルブ膜のMR特性およびそのアニール温度依存性

    永沼 博, 岡村 総一郎, 塩嵜 忠

    応用物理学会 2000年9月3日

  89. 窒化鉄粉末の合成および熱分解挙動に関する研究

    永沼 博, 小林 秀彦, 柿崎 浩一, 平塚 信之

    日本セラミックス協会 1999年3月27日

︎全件表示 ︎最初の5件までを表示

産業財産権 9

  1. マルチフェロイック素子

    永沼 博, 一ノ瀬 智浩, 大兼 幹彦, 安藤 康夫

    産業財産権の種類: 特許権

  2. トランジスタおよびその製造方法

    好田 誠, 永沼 博, 遠藤 恭, 関 剛斎, 宮崎 孝道

    産業財産権の種類: 特許権

  3. マルチフェロイック薄膜及びそれを用いたデバイス

    永沼 博, フスネ アラ ベガン, 窪田 美穂, 佐藤 敬, 大兼 幹彦, 安藤 康夫

    産業財産権の種類: 特許権

  4. 磁気抵抗素子及びそれを用いた磁気メモリ

    永沼 博, モハメド ナズルル, イスラム カーン, 井波 暢人, 大兼 幹彦, 安藤 康夫

    産業財産権の種類: 特許権

  5. 磁気抵抗効果素子および磁気デバイス

    大兼 幹彦, 佐藤 丈, 永沼 博, 安藤 康夫

    産業財産権の種類: 特許権

  6. スピントランジスタおよび磁気デバイス

    大兼 幹彦, 大平 祐介, 永沼 博, 安藤 康夫

    産業財産権の種類: 特許権

  7. 二重障壁強磁性トンネル接合および磁気デバイス

    姜 麗仙, 永沼 博, 大兼 幹彦, 安藤 康夫

    産業財産権の種類: 特許権

  8. ホイスラー合金材料、磁気抵抗素子および磁気デバイス

    大兼 幹彦, 佐藤 丈, 窪田 崇秀, 永沼 博, 安藤 康夫

    産業財産権の種類: 特許権

  9. ホイスラー合金材料、磁気抵抗素子および磁気デバイス

    大兼 幹彦, 佐藤 丈, 窪田 崇秀, 永沼 博, 安藤 康夫

    特許第5413646号

    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

担当経験のある科目(授業) 5

  1. 熱学・統計力学A 東北大学

  2. 先端スピン工学特論

  3. 物性物理学原論A 東北大学

  4. 電子材料物性A 東北大学大学院

  5. 電磁気学基礎演習 東北大学

社会貢献活動 7

  1. サイエンスアゴラ

    2018年11月9日 ~ 2018年11月10日

  2. 人工知能と材料デバイスの接点の探索

    特別講演会

    2018年9月22日 ~ 2018年9月22日

  3. リフレッシュ理科教室展示会

    2013年9月17日 ~ 2013年9月18日

    詳細を見る 詳細を閉じる

    応用物理学会の各支部により日頃のリフレッシュ理科教室で展示している工作などの意見交換およびFDについて。

  4. リフレッシュ理科教室

    2013年12月13日 ~

    詳細を見る 詳細を閉じる

    仙台市立愛宕中学校にてリフレッシュ理科教室を行った

  5. 物理学者が被災小学校で理科教室

    2013年6月28日 ~

    詳細を見る 詳細を閉じる

    全国各地から集まった物理学者たちが、被災して近くで校舎を間借りしている仙台市内の小学校で理科教室を開きました。

  6. 出前授業@仙台市立中野小学校

    2013年6月28日 ~

    詳細を見る 詳細を閉じる

    仙台市立中野小学校の復興支援のため理科教室を開催し、その主たる実行委員を務めた。

  7. 出前授業@仙台市立木町小学校

    2012年12月17日 ~

    詳細を見る 詳細を閉じる

    仙台市立木町小学校にて理科の出前教室を行う。

︎全件表示 ︎最初の5件までを表示

メディア報道 29

  1. 東北大など、ファンデルワールス力により異なる結晶界面を「つよく・しなやか」に結合できることを発見

    日本経済新聞 日本経済新聞 電子版 速報

    2022年3月2日

    メディア報道種別: インターネットメディア

  2. 東北大、CoとNの原子の相対位置関係により二次元物質と強磁性金属の界面の混成軌道による界面垂直磁気異方性強化を発見

    日本経済新聞 テック 科学&新技術

    2021年8月20日

    メディア報道種別: 新聞・雑誌

  3. 経営ひと言/東北大学・永沼博准教授「黙々と…」

    日刊工業新聞 科学技術・大学

    2021年6月18日

    メディア報道種別: 新聞・雑誌

  4. STT―MRAM向け記憶素子、書き換え耐性6000億回超 東北大

    日刊工業新聞 https://www.nikkan.co.jp/articles/view/601207?isReadConfirmed=true

    2021年6月9日

    メディア報道種別: 新聞・雑誌

  5. 東北大、「6重界面界面垂直型強磁性磁気トンネル接合素子(iPMAHexa-MTJ)」を開発

    日本経済新聞

    2022年12月5日

    メディア報道種別: 新聞・雑誌

  6. 神戸大と東北大、スピントロニクス向け強磁性合金材料と二 次元物質間の異種結晶界面の状態を第一原理計算で予測

    日本経済新聞 電子版

    2022年9月6日

    メディア報道種別: 新聞・雑誌

  7. 量子科学技術研究開発機構-東北大学 マッチング研究支援事業の採択課題が決定 次世代放射光利用研究を両機関の最先端の技術により推進

    東北大学ホームページ ホームページ

    2022年4月27日

    メディア報道種別: インターネットメディア

  8. 次世代超⾼密度MRAM記録層実現への新たな道筋 異種結晶界⾯の密度プロファイル評価にD8 DISCOVER Plusが貢献︕

    ブルカージャパン X線事業部ニュース 2022年 Vol.2

    2022年3月8日

    メディア報道種別: その他

  9. Unveiling Chemisorbed Crystallographically Heterogeneous Graphene/FePd Interface

    Mirage latest news

    2022年3月3日

    メディア報道種別: インターネットメディア

  10. ファンデルワールス力で異種結晶の結合に成功、次世代MRAMへの利用に期待

    Mapionニュース マイナビニュース

    2022年3月3日

    メディア報道種別: インターネットメディア

  11. ファンデルワールス力で異種結晶界面の結合に成功、次世代MRAMへの利用に期待

    Go to ニュース ニュース欄

    2022年3月3日

    メディア報道種別: インターネットメディア

  12. 東北大ら、ファンデルワールス力で異種界面接合

    Optronics online ニュース→化学・技術

    2022年3月2日

    メディア報道種別: インターネットメディア

  13. ファンデルワールス力による”つよく”・”しなやか”な新しい結合 -強磁性トンネル接合素子の構成材料としてグラフェン二次元物質/規則合金の異種結晶界面に期待-

    一般財団法人 総合科学研究機構 中性子科学センター ホームページ

    2022年3月2日

    メディア報道種別: その他

  14. Advance Ferromagnetic Tunnel Junctiion Using Two-dimensional Hexagonal-BN

    Alpha Galileo https://www.alphagalileo.org/en-gb/Item-Display/ItemId/211934?returnurl=https://www.alphagalileo.org/en-gb/Item-Display/ItemId/211934

    2021年8月27日

    メディア報道種別: インターネットメディア

  15. Advanced ferromagnetic tunnel junction using two dimesional hexagonal-BN

    Nano Werk https://www.nanowerk.com/nanotechnology-news2/newsid=58697.php

    2021年8月27日

    メディア報道種別: インターネットメディア

  16. Hexagonal boron nitride as a tunnel barrier for ferromagnetic tunnle junctions

    PHYS.ORG https://phys.org/news/2021-08-hexagonal-boron-nitride-tunnel-barrier.html

    2021年8月27日

    メディア報道種別: インターネットメディア

  17. Advanced Ferromagnetic Tunnel Junction Using Two-dimensional Hexagonal-BN

    MRAGE News https://www.miragenews.com/advanced-ferromagnetic-tunnel-junction-using-620505/

    2021年8月26日

    メディア報道種別: インターネットメディア

  18. MTJ素子の障壁材料に二次元物質を利用、1000%のTMR比を確認

    EE Times Japan IT

    2021年8月25日

    メディア報道種別: インターネットメディア

  19. 強磁性トンネル接合素子の障壁材料における二次元物質の可能性、東北大が調査

    Mapionニュース ネタ・コラム

    2021年8月23日

    メディア報道種別: インターネットメディア

  20. 強磁性トンネル接合素子の障壁材料における二次元物質の可能 性、東北大が調査

    マイナビニュース ITニュース・総合

    2021年8月23日

    メディア報道種別: インターネットメディア

  21. 強磁性トンネル接合素子の障壁材料として 二次元物質(六方晶窒化ホウ素)に期待 - 1,000%のTMR比と界面垂直磁気異方性の誘起を予測 - 執筆者本人

    東北大学ホームページ ホーム > 2021年のプレスリリース・研究成果

    2021年8月20日

    メディア報道種別: その他

  22. 東北大学はスピントロニクス MRAMで世界に最先行する!

    産業タイムス ST Semicon New Wave 2021 https://www.sangyo-times.jp/newwave2021/movie-07.html

    2021年4月19日

    メディア報道種別: インターネットメディア

  23. STT-MRAM の車載応用を可能にする 高速かつ高信頼な微細磁気トンネル接合(MTJ)素子の実証動作に成功 ~IoT・AI 分野から車載分野までの STT-MRAM の応用領域拡大に道を拓く~

    2020年6月6日

    メディア報道種別: その他

  24. サイエンスデイ出展 =磁石の不思議にふれてみよう!=

    2015年7月19日

    詳細を見る 詳細を閉じる

    ナチュラルサイエンスが主催するサイエンスデイに応用物理学会東北支部から出展した。超強力磁石であるNd系材料に直接触れて体感し、現在の省エネルギー技術まで理解出来るような内容となっている。

  25. サイエンスデイ出展 =磁石の不思議にふれてみよう!=

    2014年7月20日

    詳細を見る 詳細を閉じる

    小中高生を対象に磁石の不思議を体験しもらうブースを出展した。

  26. サイエンスデイ出展 =磁石の不思議にふれてみよう!=

    2013年7月21日

    詳細を見る 詳細を閉じる

    Natural Scienceが企画するサイエンスデイに応用物理学会として出展した。

  27. 磁石の力にわくわく

    河北新報(朝刊)

    2013年7月3日

    メディア報道種別: 新聞・雑誌

  28. 被災小学校で理科教室

    NHK宮城

    2013年6月28日

    メディア報道種別: テレビ・ラジオ番組

    詳細を見る 詳細を閉じる

    津波で校舎が被災し、別の学校の校舎を間借りして授業をしている仙台市の中野小学校で理科の実験教室を開催した。 これは、児童たちに理科の実験などを通して科学の楽しさを知ってもらおうと、東北や九州の応用物理学の研究者たちが開いたものです。

  29. 1平方インチ当たり5Tbクラスの次世代HDDヘッド用素子を開発

    2011年9月30日

    メディア報道種別: 新聞・雑誌

︎全件表示 ︎最初の5件までを表示

学術貢献活動 1

  1. 文部科学省科学技術・学術政策研究所NISTEP定点調査

    2018年2月19日 ~ 2018年2月19日

    学術貢献活動種別: 学術調査

その他 13

  1. 高温超電導体薄膜へのスピン注入

    詳細を見る 詳細を閉じる

    YBCO高温超電導体にスピンポンピング法によりスピン流を注入する。Tc近傍でTcがスピン注入の影響により変化することが期待されており、Tcの新しい制御方法として注目されている。

  2. 複雑なペロブスカイトの高精度な結晶対称性評価技術の確立

    詳細を見る 詳細を閉じる

    BiFeO3ペロブスカイト構造はバルクではR3cであるが、エピタキシャル薄膜となると基板からの応力により結晶対称性が変化することが知られている。しかし、これまでに高精度の構造因子計算を行い、構造解析を行った例は少ない。また、電子線回折はX線回折に比べて波長が短いため広い逆格子空間の実験が可能である。本共同研究では日本側が高品質な試料を提供し、米国側が高精度の構造解析を行い、これまで明らかになってない結晶対称性について正確に評価する技術を確立することを目的とする。

  3. スパッタ用の高品質FePd溶融ターゲットの開発

    詳細を見る 詳細を閉じる

    高品質FePdエピタキシャル膜作製のためのスパッタターゲット開発

  4. 新規の機能性磁気抵抗効果材料とその応用

    詳細を見る 詳細を閉じる

    垂直磁気異方性を自由層としたトンネル磁気抵抗素子およびマルチフェロイックをもちいた新規トンネル磁気抵抗素子によりこれまでにない新しい機能性スピンデバイスを創製することを目的とする。

  5. 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

    詳細を見る 詳細を閉じる

    磁気センサーをもちいて微弱な脳磁図および心磁図を描くことを目的としており、現行のSQUIDの代替を目的としている。

  6. 垂直磁化材料を用いたゲート電界磁化制御型スピンMOSFETの構築

    詳細を見る 詳細を閉じる

    垂直磁化材料をもちいたゲートMOSFETを構築し、さらに低消費電力化のために変調制御を電界で行う。

  7. 垂直スピン波伝搬による低消費電力通信に関する研究

    詳細を見る 詳細を閉じる

    垂直スピン伝搬により論理演算回路を創製し、従来のCu配線による電気的な信号の伝搬に比べて飛躍的に消費電力を低減させる。

  8. 二重トンネル接合素子の反強磁性固定層における貴金属元素の役割

    詳細を見る 詳細を閉じる

    二重トンネル接合素子の反強磁性固定層における貴金属元素の役割

  9. 先端スピントロニクス材料と伝導現象(ASPIMATT)

    詳細を見る 詳細を閉じる

    ホイスラー合金など新しい規則合金をもちいてスピン波伝搬を実現し、新しいマグノニクス分野を創成する。また、自励発振素子をもちいたスピン波伝搬という新しい概念にも挑戦する。

  10. 微小磁気抵抗素子のダイオード機能を利用した高感度検波素子の開発

    詳細を見る 詳細を閉じる

    スピントランスファートルク(STT)現象はマイクロ波の検波に利用できることが期待される。現在、マイクロ波帯域の電波の検出(検波)には半導体ダイオードが広く用いられている。磁性検波素子の検波能力が上回るためには、STT現象が誘起される直流印加電圧の低下、低抵抗化、高磁気抵抗比化などが課題となる。本申請は種々の課題を解決するアイディアを提案し、半導体検波素子を上回る2乗検波特性を示す磁性体検波素子の作製を目指す。

  11. マルチフェロイックトンネル接合をもちいた多値メモリの創製

    詳細を見る 詳細を閉じる

    研究代表者が発見した室温以上で自発磁化および自発分極を有するマルチフェロイック物質であるBiFeO3-BiCoO3固溶体をもちいてマルチフェロイックトンネル接合を作製し、スピンフィルター効果と自発分極の向きをそれぞれ独立に制御することにより室温以上で動作する多値メモリを創製することを目的とする。

  12. MgOおよびAlOトンネル接合におけるスピントランスファー磁化反転

    詳細を見る 詳細を閉じる

    MgOおよびAlOを障壁としたトンネル接合素子を作製し、障壁層の厚さを薄くすることによりスピントランスファートルクを顕在化させ、新しいスピンデバイスを創製する。

  13. BiFeO3薄膜の磁性に関する研究

    詳細を見る 詳細を閉じる

    化学溶液堆積(Chemical Solution Deposition)法をもちいてBiFeO3薄膜を形成し、スパッタリングにより鉄薄膜を形成し、BiFeO3薄膜/鉄薄膜の二層膜を作製する。この二層膜をもちいて反強磁性の特徴のひとつである交換結合磁界について評価し、寄生強磁性の原因となっているスパイラルスピン構造との関連について知見を得ることを目的とする。

︎全件表示 ︎最初の5件までを表示