顔写真

テヅカ ノブキ
手束 展規
Nobuki Tezuka
所属
大学院工学研究科 知能デバイス材料学専攻 情報デバイス材料学講座(スピン情報材料学分野)
職名
准教授
学位
  • 博士(工学)(東北大学)

  • 修士(工学)(東北大学)

委員歴 6

  • 日本磁気学会 現地実行委員

    2007年10月 ~ 2008年9月

  • 日本磁気学会 現地実行委員

    2007年10月 ~ 2008年9月

  • 19th International Colloquium on Magnetic Films and Surfaces現地実行委員 現地実行委員

    2006年8月 ~

  • 19th International Colloquium on Magnetic Films and Surfaces現地実行委員 現地実行委員

    2006年8月 ~

  • 第65 回応用物理学会学術講演会現地実行委員 現地実行委員

    2004年9月 ~

  • 第65 回応用物理学会学術講演会現地実行委員 現地実行委員

    2004年9月 ~

︎全件表示 ︎最初の5件までを表示

所属学協会 4

  • 日本応用物理学会

  • 日本金属学会

  • 日本物理学会

  • 日本応用磁気学会

研究分野 3

  • ナノテク・材料 / 結晶工学 /

  • ナノテク・材料 / 応用物性 /

  • ナノテク・材料 / 構造材料、機能材料 /

論文 190

  1. Increase of energy products of Zn-bonded Sm-Fe-N magnets with low oxygen content. 査読有り

    Journal of Magnetism and Magnetic Materials 467 64-68 2018年12月

    出版者・発行元:None

    DOI: 10.1016/j.jmmm.2018.07.064  

    ISSN:0304-8853

  2. Voltage control of a magnetic switching field for magnetic tunnel junctions with low resistance and perpendicular magnetic anisotropy 査読有り

    N. Tezuka, S. Oikawa, M. Matsuura, S. Sugimoto, K. Nishimura, T. Irisawa, Y. Nagamine, K. Tsunekawa

    AIP Advances 8 (5) 55922-1-55922-5 2018年5月1日

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

    DOI: 10.1063/1.5006398  

    ISSN:2158-3226

    eISSN:2158-3226

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    The authors investigated the voltage control of a magnetic anisotropy field for perpendicular-magnetic tunnel junctions (p-MTJs) with low and high resistance-area (RA) products and for synthetic antiferromagnetic free and pinned layers. It was found that the sample with low RA products was more sensitive to the applied bias voltage than the sample with high RA products. The bias voltage effect was less pronounced for our sample with the synthetic antiferromagnetic layer for high RA products compared to the MTJs with single free and pinned layers.

  3. High coercive Zn-bonded Sm-Fe-N magnets prepared using fine Zn particles with low oxygen content 査読有り

    Masashi Matsuura, Tomoki Shiraiwa, Nobuki Tezuka, Satoshi Sugimoto, Tetsuya Shoji, Noritsugu Sakuma, Kazuaki Haga

    Journal of Magnetism and Magnetic Materials 452 243-248 2018年4月15日

    出版者・発行元:Elsevier B.V.

    DOI: 10.1016/j.jmmm.2017.12.059  

    ISSN:0304-8853

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    To improve the coercivity of Zn-bonded Sm-Fe-N magnets, fine Zn particles with low oxygen content were fabricated by the hydrogen plasma-metal reaction (HPMR), and Zn-bonded Sm-Fe-N magnets were prepared using the Zn particles. The primary and secondary average Zn particle sizes were 0.23 and 0.93 μm, respectively, and the oxygen content was 0.068 wt%. The oxygen content in the Zn-bonded Sm-Fe-N magnets prepared using the Zn particles also decreased, and the coercivity and energy products of the 15 wt% Zn-bonded Sm-Fe-N magnets were 2.66 MA·m−1 and 53.1 kJ·m−3, respectively, at room temperature. The 10 wt% Zn-bonded Sm-Fe-N magnet was also a high coercivity value of 2.41 MA·m−1, and the energy product was 56.1 kJ·m−3. The coercivity strongly depended on the oxygen content rather than the particle size of Zn, and decreasing the oxygen content in the starting material improved the magnetic properties of Zn-bonded Sm-Fe-N magnets. The coercivity of the 15 wt% Zn magnet measured at 180 and 200 °C was 1.23 and 1.10 MA·m−1, respectively, and the temperature coefficient of coercivity was −0.32%·°C−1.

  4. Interfacial crystal structures and non-local spin signals of Co2FeAl0.5Si0.5/n-GaAs junctions 査読有り

    Kohei Kataoka, Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    IEEE Transactions on Magnetics 54 (1) 4400103-1-4400103-3 2018年1月1日

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

    DOI: 10.1109/TMAG.2017.2756986  

    ISSN:0018-9464

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    We have investigated interfacial crystal structures and non-local spin signals ΔR of Co2FeAl0.5Si0.5 (CFAS)/n-GaAs junctions. Cross-sectional transmission electron microscopy observations indicated that with the exception of Ga diffusion into CFAS of the sample deposited at 400 °C, the interfacial structure of the junctions and defect density at the interface were not very different for different CFAS fabrication temperatures of the substrate (TCFAS). The obtained reflection high-energy electron diffraction patterns showed that all samples fabricated at TCFAS varying from room temperature to 400 °C exhibited the L21 ordered structure in the vicinity of CFAS/n-GaAs junctions. It is found that the junctions with larger rectifying characteristic as indicated by the conduction ratio G(0.5 V)/G(-0.5 V) show larger spin signal ΔR. This may strongly affect the spin injection/detection efficiency.

  5. Effect of hydrogenation disproportionation conditions on magnetic anisotropy in Nd-Fe-B powder prepared by dynamic hydrogenation disproportionation desorption recombination 査読有り

    Masao Yamazaki, Takashi Horikawa, Chisato Mishima, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    AIP ADVANCES 7 (5) 056220 2017年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4975697  

    ISSN:2158-3226

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    Various anisotropic Nd-Fe-B magnetic powders were prepared by the dynamic hydrogenation disproportionation desorption recombination (d-HDDR) treatment with different hydrogenation disproportionation (HD) times (tHD). The resulting magnetic properties and microstructural changes were investigated. The magnetic anisotropy was decreased with increasing tHD. In the d-HDDR powders with higher magnetic anisotropy, fine (200-600 nm) and coarse (600-1200 nm) Nd2Fe14B grains were observed. The coarse Nd2Fe14B grains showed highly crystallographic alignment of the c-axis than fine Nd2Fe14B grains. In the highly anisotropic Nd2Fe14B d-HDDR powder, a large area fraction of lamellar-like structures consisting of NdH2 and alpha-Fe were observed after HD treatment. Furthermore, the mean diameter of the lamellar-like regions, where lamellar-like structures orientate to the same direction in the HD-treated alloys was close to that of coarse Nd2Fe14B grains after d-HDDR treatment. Thus, the lamellar-like regions were converted into the crystallographically aligned coarse Nd2Fe14B grains during desorption recombination treatment, and magnetic anisotropy is closely related to the volume fraction of lamellar-like regions observed after HD treatment. (C) 2017 Author(s).

  6. Effect of hydrogenation disproportionation conditions on magnetic anisotropy in Nd-Fe-B powder prepared by dynamic hydrogenation disproportionation desorption recombination. 査読有り

    手束 展規

    AIP Advances 7 (5) 056220-1-056220-8 2017年2月

  7. Study of an Al-Ca Alloy with Low Young's Modulus 査読有り

    Jun Yu, Yasuo Ishiwata, Yoshihiro Taguchi, Daisuke Shimosaka, Ryosuke Taniguchi, Takutoshi Kondo, Nobuki Tezuka

    LIGHT METALS 2017 167-171 2017年

    出版者・発行元:SPRINGER INTERNATIONAL PUBLISHING AG

    DOI: 10.1007/978-3-319-51541-0_23  

    ISSN:2367-1181

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    Aluminum alloys with low Young's Modulus have not been well studied. This study offers properties and production methods of an Al-Ca alloy. Here, an Al-Ca alloy with a small amount of Fe addition was prepared by Direct-Chill (DC) casting, extrusion and rolling, microstructure and mechanical properties were investigated after every process. Low Young's Modulus of less than 55 GPa and increased yield strength was achieved when adding heat treatment after extrusion and rolling.

  8. Improvement of Coercivity of Nd-Fe-B Powder by Nd-Cu Sputtering 査読有り

    Ami Iijima, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    MATERIALS TRANSACTIONS 58 (5) 825-828 2017年

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.M2016448  

    ISSN:1345-9678

    eISSN:1347-5320

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    This paper reports improvement of the coercivity of Nd-Fe-B powder by Nd-Cu sputtering. The total rare earth element content of the Nd-Fe-B powder increased by 0.8 mass% after Nd-Cu sputtering, and the sputtered Nd-Cu was observed at the surface of Nd-Fe-B powder by microstructural observation. The coercivity (H-c) of the Nd-Cu-sputtered Nd-Fe-B powder improved after annealing at temperatures above 600 degrees C, and H-c of the sputtered powder reached a maximum value of 1312 kA m(-1) after annealing at 900 degrees C. This H-c value was 470 kA m(-1) higher than that of Nd-Fe-B powder without sputtering. Isotropic green compacts were prepared from Nd-Fe-B powders with and without Nd-Cu sputtering, and the sputtering also improved H-c in the compacts. The compact prepared from powder with sputtering had H-c of 630 kA m(-1) higher than that of the compact prepared from powder without sputtering after annealing at 900 degrees C. Microstructure observation showed that the improvement of H-c was due to an increase in the Nd-rich phase in the compact by Nd-Cu sputtering.

  9. Effect of post annealing on spin accumulation and transport signals in Co2FeSi/MgO/n(+)-Si on insulator devices 査読有り

    Ajay Tiwari, Tomoaki Inokuchi, Mizue Ishikawa, Hideyuki Sugiyama, Nobuki Tezuka, Yoshiaki Saito

    AIP ADVANCES 6 (7) 075119 2016年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4960210  

    ISSN:2158-3226

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    The post annealing temperature dependence of spin accumulation and transport signals in Co2FeSi/MgO/n(+)-Si on insulator were investigated. The spin signals were detected using 3- and 4-terminal Hanle, 2-terminal local and 4-terminal nonlocal magnetoresistance measurements. The post annealing temperature (T-A) dependence of the magnitude in 3-terminal narrow Hanle signals is nearly constant up to T-A <400 degrees C, however a slight decrease above T-A >= 400 degrees C is observed. This behavior is consistent with the T-A dependence of the magnitude of 4-terminal nonlocal magnetoresistance (MR) signals. The spin polarization estimated from the 3-terminal narrow Hanle signals and the magnitude of 2-terminal local MR signals show a slight improvement with increasing post annealing temperature with a peak at around 325 degrees C and then start reducing slowly. The slight increase in the spin signal would be due to high spin polarization of Co2FeSi as a result of structural ordering. The 2-terminal local MR signals do not vary significantly by annealing between as-deposited and T-A = 400 degrees C, indicating the robustness of our device. This result would be useful for future Si spintronics devices. (C) 2016 Author(s).

  10. High-Coercivity Fe-Co Nanoparticles Prepared by Pulsed Arc Plasma Deposition 査読有り

    Daiki Horiyama, Masashi Matsuura, Tetsuro Yamamoto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 57 (2) 207-211 2016年2月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201510  

    ISSN:1345-9678

    eISSN:1347-5320

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    Fe-Co nanoparticles were prepared on SiO2 nanoparticles by a pulsed arc plasma deposition (APD) method and the influence of discharge count during APD on the microstructure and magnetic properties of the nanoparticles was investigated. When the discharge count was 300 shots, the average particle size (d(50)) of Fe-Co was 3.7 nm and an unusually high coercivity (H-c) of 300 kA.m(-1) was obtained. The average particle size increased and the coercivity decreased with increasing discharge count. Fe-Co nanoparticles deposited on C nanoparticles using a discharge count of 300 shots exhibited a lower coercivity than that of Fe-Co nanoparticles deposited on SiO2 nanoparticles.

  11. Spin Injection, Transport, and Detection in a Lateral Spin Transport Devices with Co2FeAl0.5Si0.5/n-GaAs, Co2FeSi/MgO/n-Si, and CoFe/MgO/n-Si Junctions 査読有り

    Nobuki Tezuka, Yoshiaki Saito

    MATERIALS TRANSACTIONS 57 (6) 767-772 2016年

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.ME201502  

    ISSN:1345-9678

    eISSN:1347-5320

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    We demonstrate spin injection, transport, and detection in a lateral spin transport devices with Co2FeAl0.5Si0.5/n-GaAs, Co2FeSi/MgO/nSi, and CoFe/MgO/n-Si junctions. Non-local four-and three-terminal Hanle-effect signals indicate large spin injection/detection efficiency in Si for Co2FeSi/MgO/Si on insulator (SOI) devices compared with CoFe/MgO/SOI devices, whereas the preparation methods of MgO layers on SOI are exactly same in both devices. The estimated spin injection/detection efficiency in GaAs is 0.06 at 4.2 K, which is also larger than those of the devices with Fe and CoFe electrodes. Different properties in the bias voltage dependences on the amplitude of spin accumulation signals are also observed between Co2FeSi/MgO/SOI and CoFe/MgO/SOI devices. These results indicate that the species of ferromagnetic material definitely influences the amplitude and the behavior of the spin signals.

  12. Perpendicular Magnetic Tunnel Junctions With Low Resistance-Area Product: High Output Voltage and Bias Dependence of Magnetoresistance 査読有り

    N. Tezuka, S. Oikawa, I. Abe, M. Matsuura, S. Sugimoto, K. Nishimura, T. Seino

    IEEE MAGNETICS LETTERS 7 3104104-3104204 2016年

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

    DOI: 10.1109/LMAG.2016.2584582  

    ISSN:1949-307X

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    We investigate the tunnel magnetoresistance (TMR) effect and its applied bias voltage dependence for perpendicular magnetic tunnel junctions (p-MTJs) with low resistance-area (RA) products of about 10 Omega . mu m(2). We obtain a maximum TMR ratio of 248% among the examined devices. The bias-voltage dependence of the TMR ratio for these junctions is almost the same as that for junctions with RA products of about 10-1000 Omega . mu m(2) in the positive voltage region, while a fast drop in the TMR ratio is observed in the negative bias region. An output voltage of more than 200 mV is obtained for these p-MTJs.

  13. Influence of Swaging on the Magnetic Properties of Zn-Bonded Sm-Fe-N Magnets 査読有り

    Kohei Kataoka, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 56 (10) 88-92 2015年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.M2015190  

    ISSN:1345-9678

    eISSN:1347-5320

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    Swaging was investigated as a fabrication process for high-density Zn-bonded Sm-Fe-N magnets, which mainly consisted of Sm2Fe17Nx, and their magnetic properties were investigated. The demagnetization curves of the annealed specimens with or without swaging suggested that swaging improved the magnetic polarization. The specimen swaged with a reduction ratio (R) of 82%, a high maximum energy product ((BH)(max)) of 67.8 kJ.m(-3) with a high coercivity (H-cJ) of 1.89 MA.m(-1) was obtained. Sm-Fe-N particles were pulverized and the dispersion of Zn particles was improved during swaging, the density of specimens increased resulting in the increase in H-cJ and (BH)(max).

  14. Increased uniaxial perpendicular anisotropy in tetragonally distorted FeCo-Ti-N films 査読有り

    Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF APPLIED PHYSICS 117 (17) 17A738 2015年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4916763  

    ISSN:0021-8979

    eISSN:1089-7550

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    Tetragonally distorted FeCo-Ti-N films were prepared on a Rh(001) underlayer. Uniaxial perpendicular anisotropy was observed for FeCo-Ti-N films with a thickness of 23.5 nm, and the c/a lattice distortion reached 1.08. The anisotropy constant (K-u) was estimated to be a minimum of 0.57 MJ.m(-3) (5.7 x 10(6) ergs.cm(-3)). These results show that the combination of Ti and N additive elements could be effective for inducing lattice distortion in FeCo-based alloys on a Rh under layer, and that the lattice distortion increases K-u. (C) 2015 AIP Publishing LLC.

  15. Correlation between amplitude of spin accumulation signals investigated by Hanle effect measurement and effective junction barrier height in CoFe/MgO/n(+)-Si junctions 査読有り

    Y. Saito, M. Ishikawa, H. Sugiyama, T. Inokuchi, K. Hamaya, N. Tezuka

    JOURNAL OF APPLIED PHYSICS 117 (17) 17C707 2015年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4907242  

    ISSN:0021-8979

    eISSN:1089-7550

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    Correlation between the amplitude of the spin accumulation signals and the effective barrier height estimated from the slope of the log (RA) -t(MgO) plot (RA: resistance area product, t(MgO): thickness of MgO tunnel barrier) in CoFe/MgO/n(+)-Si junctions was investigated. The amplitude of spin accumulation signals increases with increasing effective barrier heights. This increase of the amplitude of spin accumulation is originated from the increase of the spin polarization (P-Si) in Si. The estimated absolute values of P-Si using three-terminal Hanle signals are consistent with those estimated by four-terminal nonlocal-magnetoresistance (MR) and two-terminal local-MR. To demonstrate large spin accumulation in Si bulk band and enhance the local-MR through Si channel, these results indicate that the increase of the effective barrier height at ferromagnet/(tunnel barrier)/n(+)-Si junction electrode is important. (C) 2015 AIP Publishing LLC.

  16. Effects of Hydrogenation-Disproportionation-Desorption-Recombination Processing Parameters on the Particle Size of Ultrafine Jet-Milled Nd-Fe-B Powders 査読有り

    Michihide Nakamura, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    MATERIALS TRANSACTIONS 56 (1) 129-134 2015年1月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.M2014273  

    ISSN:1345-9678

    eISSN:1347-5320

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    The effects of variations in the hydrogenation-disproportionation-desorption-recombination (HDDR) processing parameters on the size of Nd-Fe-B ultrafine powders were investigated. The ultrafine powders were fabricated by hydrogen decrepitation and jet milling of the HDDR alloys. Before pulverization, the crystal grain size of the HDDR alloys obtained by changing the HD processing temperature (T-HD) varied from 0.27 to 0.55 mu m, and decreased as T-HD was lowered. The ultrafine powder of the HDDR alloy became finer as T-HD decreased, with sizes in the range of 0.33 to 0.58 mu m.

  17. Comparison of Spin Signals Between 3T Hanle and 4T Non-Local Methods for Co2Fe(Al,Si)/n-GaAs Junctions 査読有り

    Nobuki Tezuka, Tatsuya Saito, Masashi Matsuura, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 50 (11) 2600204 2014年11月

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

    DOI: 10.1109/TMAG.2014.2325942  

    ISSN:0018-9464

    eISSN:1941-0069

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    We investigated spin signals for Co2Fe(Al,Si)/n-GaAs Shottoky tunnel junctions by three terminal (3T) Hanle and four terminal (4T) non-local measurements. The ordering structure and magnetic moment increased with T-CFAS up to 300 degrees C. The spin signals for Co2Fe(Al, Si)/n-GaAs Shottky tunnel junctions were clearly observed and these were also affected by T-CFAS, however, the T-CFAS dependency was different obtained from 3T Hanle and 4T non-local measurements. The spin signals in 3T Hanle measurement decreases with increasing T-CFAS up to 300 degrees C and increase for the sample with T-CFAS = 400 degrees C. On the other hand, the spin signals in 4T non-local measurement increases with T-CFAS up to 300 degrees C and decreases for the sample with T-CFAS = 400 degrees C. This result obtained from 4T non-local measurement could be explained by the spin polarization of Co2Fe(Al,Si), and that from 3T Hanle measurement would not come from the spin polarization of Co2Fe(Al, Si) but other source, such as localized state around the interface between Co2Fe(Al,Si) and n-GaAs.

  18. Effect of Annealing on Magnetic Properties of Ultrafine Jet-Milled Nd-Fe-B Powders 査読有り

    Michihide Nakamura, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    MATERIALS TRANSACTIONS 55 (10) 1582-1586 2014年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201402  

    ISSN:1345-9678

    eISSN:1347-5320

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    This paper reports the effects of annealing on the magnetic properties of ultrafine Nd-Fe-B powders with an average particle size of 0.67 mu m. The powder was fabricated from hydrogenation disproportionation-desorption-recombination (HDDR)-treated Nd-Fe-B alloys by hydrogen decrepitation and helium jet milling. The coercivity of the ultrafine powders was slightly increased by annealing below 500 degrees C, and was drastically increased by annealing above 600 degrees C. These two stepwise increases in coercivity were attributed to hydrogen desorption and formation of a liquid Nd-rich phase. In addition, after annealing below 500 degrees C, the coercivity (mu H-0(c)) of the ultrafine powder was higher than that of the conventional powder, which was prepared from a strip-cast Nd-Fe-B alloy power with a particle size of 1.12 mu m, because of a decrease in particle size. In contrast, after annealing above 600 degrees C, the mu H-0(c), of the ultrafine powder was smaller than that of the conventional powder. The rare earth element content (Nd + Pr) was lower in the ultrafine powders than in the conventional powder. These results indicate that the rare earth element content was insufficient in the ultrafine powders.

  19. Microstructure and coercivity of nitrided Mn-Sn-based alloys 査読有り

    Masashi Matsuura, Keita Isogai, Keita Shinaji, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF ALLOYS AND COMPOUNDS 605 208-212 2014年8月

    出版者・発行元:ELSEVIER SCIENCE SA

    DOI: 10.1016/j.jallcom.2014.03.158  

    ISSN:0925-8388

    eISSN:1873-4669

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    The microstructure of Mn-Sn-N and Mn-Sn-Co-N alloys was investigated by scanning electron microscopy and transmission electron microscopy (TEM). After the Mn-Sn alloy was annealed at 1000 degrees C under nitrogen, the coercivity increased to 245 kA m (1) and a lamellar structure appeared. The TEM images showed that the lamellar structure contained twins in the perovskite-type phase. After the Mn-Sn-Co alloy was annealed at 900 degrees C and subsequently annealed at 500 degrees C under nitrogen, the coercivity increased dramatically to 1270 kA m (1). A fine two-phase structure consisting of beta-Mn and perovskite-type phases was observed, and some twins were present in the perovskite-type phases. In addition, a higher twin density was observed in the Mn-Sn-Co-N alloy than in the Mn-Sn-N alloy. These results indicate that the twins increased the coercivity of nitrided Mn-Sn based alloys. (C) 2014 Elsevier B.V. All rights reserved.

  20. Microstructure and coercivity of nitrided Mn-Sn-based alloys 査読有り

    Masashi Matsuura, Keita Isogai, Keita Shinaji, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF ALLOYS AND COMPOUNDS 605 208-212 2014年8月

    出版者・発行元:ELSEVIER SCIENCE SA

    DOI: 10.1016/j.jallcom.2014.03.158  

    ISSN:0925-8388

    eISSN:1873-4669

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    The microstructure of Mn-Sn-N and Mn-Sn-Co-N alloys was investigated by scanning electron microscopy and transmission electron microscopy (TEM). After the Mn-Sn alloy was annealed at 1000 degrees C under nitrogen, the coercivity increased to 245 kA m (1) and a lamellar structure appeared. The TEM images showed that the lamellar structure contained twins in the perovskite-type phase. After the Mn-Sn-Co alloy was annealed at 900 degrees C and subsequently annealed at 500 degrees C under nitrogen, the coercivity increased dramatically to 1270 kA m (1). A fine two-phase structure consisting of beta-Mn and perovskite-type phases was observed, and some twins were present in the perovskite-type phases. In addition, a higher twin density was observed in the Mn-Sn-Co-N alloy than in the Mn-Sn-N alloy. These results indicate that the twins increased the coercivity of nitrided Mn-Sn based alloys. (C) 2014 Elsevier B.V. All rights reserved.

  21. Large spin-accumulation signal in Si for epitaxial CoFe/highly (100)-textured MgO/Si devices 査読有り

    H. Sugiyama, M. Ishikawa, T. Inokuchi, T. Tanamoto, Y. Saito, N. Tezuka

    SOLID STATE COMMUNICATIONS 190 49-52 2014年7月

    出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD

    DOI: 10.1016/j.ssc.2014.03.019  

    ISSN:0038-1098

    eISSN:1879-2766

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    Spin-accumulation in Si for epitaxial CoFe/highly (100)-textured MgO/Si devices is investigated and compared to that for CoFe/polycrystalline or (110)-textured MgO/Si devices. We find that magnesium (Mg) insertion between MgO and Si leads to highly (100)-textured MgO and epitaxial CoFe films. Interface resistance dependence on magnitude of spin-accumulation signal by the three-terminal Hanle measurement is quantitatively evaluated. Devices with highly (100)-textured MgO show larger magnitude of spinaccumulation signal in the low-interface-resistance region, than that with polycrystalline or (110)-textured MgO. These results indicate that magnitude of spin-accumulation signal depends on the crystallinity or the texture of ferromagnet/tunnel barrier layers on Si. (C) 2014 Elsevier Ltd. All rights reserved.

  22. Large spin-accumulation signal in Si for epitaxial CoFe/highly (100)-textured MgO/Si devices 査読有り

    H. Sugiyama, M. Ishikawa, T. Inokuchi, T. Tanamoto, Y. Saito, N. Tezuka

    SOLID STATE COMMUNICATIONS 190 49-52 2014年7月

    出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD

    DOI: 10.1016/j.ssc.2014.03.019  

    ISSN:0038-1098

    eISSN:1879-2766

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    Spin-accumulation in Si for epitaxial CoFe/highly (100)-textured MgO/Si devices is investigated and compared to that for CoFe/polycrystalline or (110)-textured MgO/Si devices. We find that magnesium (Mg) insertion between MgO and Si leads to highly (100)-textured MgO and epitaxial CoFe films. Interface resistance dependence on magnitude of spin-accumulation signal by the three-terminal Hanle measurement is quantitatively evaluated. Devices with highly (100)-textured MgO show larger magnitude of spinaccumulation signal in the low-interface-resistance region, than that with polycrystalline or (110)-textured MgO. These results indicate that magnitude of spin-accumulation signal depends on the crystallinity or the texture of ferromagnet/tunnel barrier layers on Si. (C) 2014 Elsevier Ltd. All rights reserved.

  23. Local magnetoresistance through Si and its bias voltage dependence in ferromagnet/MgO/silicon-on-insulator lateral spin valves 査読有り

    Y. Saito, T. Tanamoto, M. Ishikawa, H. Sugiyama, T. Inokuchi, K. Hamaya, N. Tezuka

    JOURNAL OF APPLIED PHYSICS 115 (17) 17C514 2014年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4866699  

    ISSN:0021-8979

    eISSN:1089-7550

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    Local magnetoresistance (MR) through silicon (Si) and its bias voltage (V-bias) (bias current (I-bias)) dependence in ferromagnet (FM)/MgO/silicon-on-insulator lateral spin valves are investigated. From the experimental measurements, we find that the local-MR through Si increases with increasing V-bias. This anomalous increase of local-MR as a function of V-bias can be understood by considering the standard drift-diffusion theory improved by taking into account the difference in the interface resistances and first order quantum effect between FM/MgO/Si (source) and Si/MgO/FM (drain) interfaces. The interface resistance dependence on experimentally obtained local-MR ratios also agrees with the improved standard spin diffusion theory. These results indicate that experimentally observed local-MR is certainly related to the spin signal through the Si bulk band. (C) 2014 AIP Publishing LLC.

  24. Local magnetoresistance through Si and its bias voltage dependence in ferromagnet/MgO/silicon-on-insulator lateral spin valves 査読有り

    Y. Saito, T. Tanamoto, M. Ishikawa, H. Sugiyama, T. Inokuchi, K. Hamaya, N. Tezuka

    JOURNAL OF APPLIED PHYSICS 115 (17) 17C514 2014年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4866699  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Local magnetoresistance (MR) through silicon (Si) and its bias voltage (V-bias) (bias current (I-bias)) dependence in ferromagnet (FM)/MgO/silicon-on-insulator lateral spin valves are investigated. From the experimental measurements, we find that the local-MR through Si increases with increasing V-bias. This anomalous increase of local-MR as a function of V-bias can be understood by considering the standard drift-diffusion theory improved by taking into account the difference in the interface resistances and first order quantum effect between FM/MgO/Si (source) and Si/MgO/FM (drain) interfaces. The interface resistance dependence on experimentally obtained local-MR ratios also agrees with the improved standard spin diffusion theory. These results indicate that experimentally observed local-MR is certainly related to the spin signal through the Si bulk band. (C) 2014 AIP Publishing LLC.

  25. Maximum magnitude in bias-dependent spin accumulation signals of CoFe/MgO/Si on insulator devices 査読有り

    M. Ishikawa, H. Sugiyama, T. Inokuchi, T. Tanamoto, K. Hamaya, N. Tezuka, Y. Saito

    JOURNAL OF APPLIED PHYSICS 114 (24) 243904 2013年12月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4856955  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We study in detail how the bias voltage (V-bias) and interface resistance (RA) depend on the magnitude of spin accumulation signals (vertical bar Delta V or vertical bar Delta vertical bar/I, where I is current) as detected by three-terminal Hanle measurements in CoFe/MgO/Si on insulator (SOD devices with various MgO layer thicknesses and SOI carrier densities. We find the apparent maximum magnitude of spin polarization as a function of V-bias and the correlation between the magnitude of spin accumulation signals and the shape of differential conductance (dI/dV) curves within the framework of the standard spin diffusion model. All of the experimental results can be explained by taking into account the density of states (DOS) in CoFe under the influence of the applied Vbi and the quality of MgO tunnel barrier. These results indicate that it is important to consider the DOS of the ferromagnetic materials under the influence of an applied V-bias and the quality of tunnel barrier when observing large spin accumulation signals in Si. (C) 2013 AIP Publishing LLC.

  26. Maximum magnitude in bias-dependent spin accumulation signals of CoFe/MgO/Si on insulator devices 査読有り

    M. Ishikawa, H. Sugiyama, T. Inokuchi, T. Tanamoto, K. Hamaya, N. Tezuka, Y. Saito

    JOURNAL OF APPLIED PHYSICS 114 (24) 243904 2013年12月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4856955  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We study in detail how the bias voltage (V-bias) and interface resistance (RA) depend on the magnitude of spin accumulation signals (vertical bar Delta V or vertical bar Delta vertical bar/I, where I is current) as detected by three-terminal Hanle measurements in CoFe/MgO/Si on insulator (SOD devices with various MgO layer thicknesses and SOI carrier densities. We find the apparent maximum magnitude of spin polarization as a function of V-bias and the correlation between the magnitude of spin accumulation signals and the shape of differential conductance (dI/dV) curves within the framework of the standard spin diffusion model. All of the experimental results can be explained by taking into account the density of states (DOS) in CoFe under the influence of the applied Vbi and the quality of MgO tunnel barrier. These results indicate that it is important to consider the DOS of the ferromagnetic materials under the influence of an applied V-bias and the quality of tunnel barrier when observing large spin accumulation signals in Si. (C) 2013 AIP Publishing LLC.

  27. Influence of Heat Treatment on the Microstructure and Magnetic Properties of Mn-Sn-Co-N Alloys 査読有り

    Keita Shinaji, Tsuyoshi Mase, Keita Isogai, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 54 (10) 2007-2010 2013年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201312  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    This paper describes the influence of heat treatment on the microstructure and magnetic properties of Mn-Sn-Co-N alloys. After homogenization at 950 degrees C for 20h in Ar, Mn82.5Sn10Co7.5 alloys were annealed at 900 degrees C for 1-20 h in N-2 and quenched to room temperature (first-annealing). The alloys were subsequently annealed at 400-700 degrees C for 5 h in N-2 and quenched to room temperature (second-annealing). The coercivity of the alloys changed drastically by the second annealing. The samples subjected to second annealing at 500 C showed maximum coercivity of 1270 kAm(-1) and exhibited a fine two-phase microstructure. Wavelength Dispersive X-ray Spectrometer (WDS) and X-ray Diffraction (XRD) analyses revealed that the fine two-phase microstructure consists of beta-Mn and perovskite-type (Mn4N-like) phases, as well as that the zeta two phases emerged from the phase during the second-annealing at 500 degrees C.

  28. Spin injection, transport, and detection at room temperature in a lateral spin transport device with Co2FeAl0.5Si 0.5/n-GaAs schottky tunnel junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    Applied Physics Express 6 (10) 103006 2013年10月

    DOI: 10.7567/APEX.6.103006  

    ISSN:1882-0778 1882-0786

    詳細を見る 詳細を閉じる

    We observed spin-valve signals and Hanle signals in four-terminal nonlocal measurements on a lateral spin transport device with Co2FeAl 0.5Si0.5(CFAS)/n-GaAs Schottky tunnel junctions. The estimated spin injection/detection efficiency was 0.06 at 4.2 K, which is larger than those of the devices with Fe and CoFe electrodes [Nature Physics 3 (2007) 197 and Appl. Phys. Lett. 99 (2011) 082108]. The spin diffusion length estimated from Hanle signals was consistent with the gap length dependency of the spin-valve signals. Furthermore, the spin-valve signals were observed at up to 290 K. This is the first demonstration of detecting spin accumulation in semiconductor with full-Heusler alloys electrodes at room temperature. © 2013 The Japan Society of Applied Physics.

  29. Influence of Heat Treatment on the Microstructure and Magnetic Properties of Mn-Sn-Co-N Alloys 査読有り

    Keita Shinaji, Tsuyoshi Mase, Keita Isogai, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 54 (10) 2007-2010 2013年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201312  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    This paper describes the influence of heat treatment on the microstructure and magnetic properties of Mn-Sn-Co-N alloys. After homogenization at 950 degrees C for 20h in Ar, Mn82.5Sn10Co7.5 alloys were annealed at 900 degrees C for 1-20 h in N-2 and quenched to room temperature (first-annealing). The alloys were subsequently annealed at 400-700 degrees C for 5 h in N-2 and quenched to room temperature (second-annealing). The coercivity of the alloys changed drastically by the second annealing. The samples subjected to second annealing at 500 C showed maximum coercivity of 1270 kAm(-1) and exhibited a fine two-phase microstructure. Wavelength Dispersive X-ray Spectrometer (WDS) and X-ray Diffraction (XRD) analyses revealed that the fine two-phase microstructure consists of beta-Mn and perovskite-type (Mn4N-like) phases, as well as that the zeta two phases emerged from the phase during the second-annealing at 500 degrees C.

  30. Spin injection, transport, and detection at room temperature in a lateral spin transport device with Co2FeAl0.5Si 0.5/n-GaAs schottky tunnel junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    Applied Physics Express 6 (10) 103006 2013年10月

    DOI: 10.7567/APEX.6.103006  

    ISSN:1882-0778 1882-0786

    詳細を見る 詳細を閉じる

    We observed spin-valve signals and Hanle signals in four-terminal nonlocal measurements on a lateral spin transport device with Co2FeAl 0.5Si0.5(CFAS)/n-GaAs Schottky tunnel junctions. The estimated spin injection/detection efficiency was 0.06 at 4.2 K, which is larger than those of the devices with Fe and CoFe electrodes [Nature Physics 3 (2007) 197 and Appl. Phys. Lett. 99 (2011) 082108]. The spin diffusion length estimated from Hanle signals was consistent with the gap length dependency of the spin-valve signals. Furthermore, the spin-valve signals were observed at up to 290 K. This is the first demonstration of detecting spin accumulation in semiconductor with full-Heusler alloys electrodes at room temperature. © 2013 The Japan Society of Applied Physics.

  31. Four-terminal nonlocal signals in lateral spin transport devices with variously ordered Co2FeAl0.5Si0.5 full-Heusler alloy electrodes 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    Applied Physics Letters 103 (12) 122401 2013年9月16日

    DOI: 10.1063/1.4821451  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    The structural ordering of the Co2FeAl0.5Si 0.5 (CFAS) full-Heusler alloy, the electrical transport properties, and the four-terminal (4T) nonlocal signals were investigated in lateral spin transport devices with CFAS/n-GaAs Schottky tunnel junctions as a function of the deposition temperature of CFAS (TCFAS). The 4T nonlocal signals increased with increasing TCFAS, in contrast to the trend in three-terminal Hanle measurements [Jpn. J. Appl. Phys., Part 1 52, 063001 (2013)]. No relationship between interface resistance and 4T nonlocal signal was confirmed, indicating that conductance mismatch problems did not affect the tendency of signal values. © 2013 AIP Publishing LLC.

  32. Four-terminal nonlocal signals in lateral spin transport devices with variously ordered Co2FeAl0.5Si0.5 full-Heusler alloy electrodes 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    Applied Physics Letters 103 (12) 122401 2013年9月16日

    DOI: 10.1063/1.4821451  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    The structural ordering of the Co2FeAl0.5Si 0.5 (CFAS) full-Heusler alloy, the electrical transport properties, and the four-terminal (4T) nonlocal signals were investigated in lateral spin transport devices with CFAS/n-GaAs Schottky tunnel junctions as a function of the deposition temperature of CFAS (TCFAS). The 4T nonlocal signals increased with increasing TCFAS, in contrast to the trend in three-terminal Hanle measurements [Jpn. J. Appl. Phys., Part 1 52, 063001 (2013)]. No relationship between interface resistance and 4T nonlocal signal was confirmed, indicating that conductance mismatch problems did not affect the tendency of signal values. © 2013 AIP Publishing LLC.

  33. Crystal Structures and Spin Injection Signals of Si/Mg/MgO/Co2FeAl0.5Si0.5 Junctions 査読有り

    Takashi Onodera, Masahiro Yoshida, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto, Yoshiaki Saito

    MATERIALS TRANSACTIONS 54 (8) 1392-1395 2013年8月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.M2013139  

    ISSN:1345-9678

    eISSN:1347-5320

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    We investigated the crystal structures and the spin injection signals of Si/Mg/MgO/Co2FeAl0.5Si0.5 (CFAS) junctions deposited by molecule beam epitaxy. The (001)-orientation and the structural ordering of CFAS thin films changed by heating deposition of CFAS and the insertion of Mg layer into Si/MgO interface. Spin injection signals observed at 10 K for the junctions by 3 terminals Hanle measurements. The maximum voltage change, Delta V-MAX, was increased by heating deposition of CFAS and the insertion of Mg layer. It is supposed that the enhancement of spin polarization by the improvement of structural ordering of CFAS or coherent tunneling by (001)-oriented MgO barrier caused the increment of Delta V-MAX.

  34. Crystal Structures and Spin Injection Signals of Si/Mg/MgO/Co2FeAl0.5Si0.5 Junctions 査読有り

    Takashi Onodera, Masahiro Yoshida, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto, Yoshiaki Saito

    MATERIALS TRANSACTIONS 54 (8) 1392-1395 2013年8月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.M2013139  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    We investigated the crystal structures and the spin injection signals of Si/Mg/MgO/Co2FeAl0.5Si0.5 (CFAS) junctions deposited by molecule beam epitaxy. The (001)-orientation and the structural ordering of CFAS thin films changed by heating deposition of CFAS and the insertion of Mg layer into Si/MgO interface. Spin injection signals observed at 10 K for the junctions by 3 terminals Hanle measurements. The maximum voltage change, Delta V-MAX, was increased by heating deposition of CFAS and the insertion of Mg layer. It is supposed that the enhancement of spin polarization by the improvement of structural ordering of CFAS or coherent tunneling by (001)-oriented MgO barrier caused the increment of Delta V-MAX.

  35. Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation-disproportionation-desorption-recombination and hydrogen decrepitation processes 査読有り

    Michihide Nakamura, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    APPLIED PHYSICS LETTERS 103 (2) 22404 2013年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4813399  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Dy addition is used to increase the coercivity of Nd-Fe-B sintered magnets. Given that Dy is rare and expensive, a method is needed for reducing the Dy content in such magnets without decreasing their coercivity. Refining Nd2Fe14B grains is a prospective method for increasing the coercivity of Nd-Fe-B magnets. Conventional jet milling, however, cannot crush strip-casted Nd-Fe-B alloys into powders less than 1 mu m in size. We report a process for preparing ultrafine jet-milled powders with an average size of 0.33 mu m for Nd-Fe-B sintered magnets: a combination of hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and He jet milling. (C) 2013 AIP Publishing LLC.

  36. Non-Local and Local Spin Signals in a Lateral Spin Transport Device With Co2FeAl0.5Si0.5/n-GaAs Schottky Tunnel Junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 49 (7) 4327-4330 2013年7月

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

    DOI: 10.1109/TMAG.2013.2248053  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We investigated magnetoresistance (MR) effects in four-terminal (4T) nonlocal and local measurements of a lateral spin transport device with Co2FeAl0.5Si0.5 (CFAS)/n-GaAs Schottky tunnel junctions. Clear voltage changes as a function of magnetic field were observed in both measurements, and these signals were confirmed to originate from spin injection, transport, and detection in the device. The values of voltage change in both measurements, Delta V-nonlocal and Delta V-local, increased linearly as a function of bias current. The MR ratio in local measurement could be explained by the conductivity mismatch theory. The nonlocal and local measurements in various circuit configurations indicated that the magnitude of Delta V-local was enhanced not only by an increase in spin transport length in the n-GaAs channel but also by an enhancement of spin detection efficiency at the CFAS/n-GaAs interface.

  37. Microwave absorption properties of polymer composites with amorphous Fe-B and Ni-Zn-Co ferrite nanoparticles 査読有り

    Kazuaki Shimba, Shozo Yuki, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY 62 (12) 2123-2127 2013年7月

    出版者・発行元:KOREAN PHYSICAL SOC

    DOI: 10.3938/jkps.62.2123  

    ISSN:0374-4884

    詳細を見る 詳細を閉じる

    Nowadays, many communication devices use GHz-range microwaves, which cause serious issues, such as electromagnetic interference. For the prevention of these problems, microwave absorbers consisting of polymer composites with magnetic particles have received attention. With the current trend being to miniaturize devices, thin microwave absorber are now required. This paper reports that polymer composites with amorphous Fe-B submicrometer particles and Ni-Zn-Co ferrite nanoparticles showed a permeability of A mu (r) ' = 8.0-9.0 at 1.0 GHz and a resonant frequency of f (r) = 1.8-2.4 GHz. They also exhibited good microwave absorption properties at 0.7-1.4 GHz for thicknesses of 2.5-3.9 mm.

  38. Non-Local and Local Spin Signals in a Lateral Spin Transport Device With Co2FeAl0.5Si0.5/n-GaAs Schottky Tunnel Junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 49 (7) 4327-4330 2013年7月

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

    DOI: 10.1109/TMAG.2013.2248053  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We investigated magnetoresistance (MR) effects in four-terminal (4T) nonlocal and local measurements of a lateral spin transport device with Co2FeAl0.5Si0.5 (CFAS)/n-GaAs Schottky tunnel junctions. Clear voltage changes as a function of magnetic field were observed in both measurements, and these signals were confirmed to originate from spin injection, transport, and detection in the device. The values of voltage change in both measurements, Delta V-nonlocal and Delta V-local, increased linearly as a function of bias current. The MR ratio in local measurement could be explained by the conductivity mismatch theory. The nonlocal and local measurements in various circuit configurations indicated that the magnitude of Delta V-local was enhanced not only by an increase in spin transport length in the n-GaAs channel but also by an enhancement of spin detection efficiency at the CFAS/n-GaAs interface.

  39. Microwave absorption properties of polymer composites with amorphous Fe-B and Ni-Zn-Co ferrite nanoparticles 査読有り

    Kazuaki Shimba, Shozo Yuki, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY 62 (12) 2123-2127 2013年7月

    出版者・発行元:KOREAN PHYSICAL SOC

    DOI: 10.3938/jkps.62.2123  

    ISSN:0374-4884

    詳細を見る 詳細を閉じる

    Nowadays, many communication devices use GHz-range microwaves, which cause serious issues, such as electromagnetic interference. For the prevention of these problems, microwave absorbers consisting of polymer composites with magnetic particles have received attention. With the current trend being to miniaturize devices, thin microwave absorber are now required. This paper reports that polymer composites with amorphous Fe-B submicrometer particles and Ni-Zn-Co ferrite nanoparticles showed a permeability of A mu (r) ' = 8.0-9.0 at 1.0 GHz and a resonant frequency of f (r) = 1.8-2.4 GHz. They also exhibited good microwave absorption properties at 0.7-1.4 GHz for thicknesses of 2.5-3.9 mm.

  40. Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation-disproportionation-desorption-recombination and hydrogen decrepitation processes 査読有り

    Michihide Nakamura, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    APPLIED PHYSICS LETTERS 103 (2) 022404 2013年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4813399  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Dy addition is used to increase the coercivity of Nd-Fe-B sintered magnets. Given that Dy is rare and expensive, a method is needed for reducing the Dy content in such magnets without decreasing their coercivity. Refining Nd2Fe14B grains is a prospective method for increasing the coercivity of Nd-Fe-B magnets. Conventional jet milling, however, cannot crush strip-casted Nd-Fe-B alloys into powders less than 1 mu m in size. We report a process for preparing ultrafine jet-milled powders with an average size of 0.33 mu m for Nd-Fe-B sintered magnets: a combination of hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and He jet milling. (C) 2013 AIP Publishing LLC.

  41. Three-Terminal Hanle Signals in Schottky Tunnel Junctions with Co2FeAl0.5Si0.5 Full-Heusler Alloy Electrodes Deposited at Various Temperatures 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (6) UNSP 063001 2013年6月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.52.063001  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigated the crystal structures, electrical transport properties, and three-terminal (3T) Hanle signals of Co2FeAl0.5Si0.5 (CFAS)/n-GaAs Schottky tunnel junctions fabricated with different deposition temperature of the CFAS (T-CFAS). CFAS thin films were deposited on the n-GaAs at T-CFAS ranging from room temperature to 300 degrees C, and 3T-Hanle signals were observed for all CFAS/n-GaAs junctions. Although the degree of structural ordering in the CFAS electrodes decreased and the rectifying characteristic disappeared as T-CFAS decreased, the spin resistance area products (Delta RA) increased and the estimated spin relaxation time (tau) decreased monotonically with decreasing T-CFAS. Moreover, the bias voltage dependence of Delta RA and tau became larger and smaller with decreasing T-CFAS, respectively. (C) 2013 The Japan Society of Applied Physics

  42. Three-Terminal Hanle Signals in Schottky Tunnel Junctions with Co2FeAl0.5Si0.5 Full-Heusler Alloy Electrodes Deposited at Various Temperatures 査読有り

    Tatsuya Saito, Nobuki Tezuka, Masashi Matsuura, Satoshi Sugimoto

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

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.52.063001  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigated the crystal structures, electrical transport properties, and three-terminal (3T) Hanle signals of Co2FeAl0.5Si0.5 (CFAS)/n-GaAs Schottky tunnel junctions fabricated with different deposition temperature of the CFAS (T-CFAS). CFAS thin films were deposited on the n-GaAs at T-CFAS ranging from room temperature to 300 degrees C, and 3T-Hanle signals were observed for all CFAS/n-GaAs junctions. Although the degree of structural ordering in the CFAS electrodes decreased and the rectifying characteristic disappeared as T-CFAS decreased, the spin resistance area products (Delta RA) increased and the estimated spin relaxation time (tau) decreased monotonically with decreasing T-CFAS. Moreover, the bias voltage dependence of Delta RA and tau became larger and smaller with decreasing T-CFAS, respectively. (C) 2013 The Japan Society of Applied Physics

  43. Crystal structure and spin conduction property of Co2FeAl 0.5Si0.5 full-heusler alloy thin films deposited on Si substrates 査読有り

    Masahiro Yoshida, Takashi Onodera, Nobuki Tezuka, Satoshi Sugimoto, Yoshiaki Saito

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals 77 (3) 85-88 2013年3月

    DOI: 10.2320/jinstmet.77.85  

    ISSN:0021-4876

    詳細を見る 詳細を閉じる

    We investigated the crystal structure and spin conduction property of Co2FeAl0.5Si0.5 (CFAS) full-Heusler alloy thin films deposited on Si substrate. The multilayer films with different barrier layer were deposited by RF magnetron sputtering system to compare their spin conduction properties. Spin injection signals were observed only with Si sub.//Mg/MgO/CFAS structure. It is considered that the crystal structure near the interface changed by insertion of Mg layer affected the spin conduction property. © 2013 The Japan Institute of Metals and Materials.

  44. Crystal structure and spin conduction property of Co2FeAl 0.5Si0.5 full-heusler alloy thin films deposited on Si substrates 査読有り

    Masahiro Yoshida, Takashi Onodera, Nobuki Tezuka, Satoshi Sugimoto, Yoshiaki Saito

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals 77 (3) 85-88 2013年3月

    DOI: 10.2320/jinstmet.77.85  

    ISSN:0021-4876

    詳細を見る 詳細を閉じる

    We investigated the crystal structure and spin conduction property of Co2FeAl0.5Si0.5 (CFAS) full-Heusler alloy thin films deposited on Si substrate. The multilayer films with different barrier layer were deposited by RF magnetron sputtering system to compare their spin conduction properties. Spin injection signals were observed only with Si sub.//Mg/MgO/CFAS structure. It is considered that the crystal structure near the interface changed by insertion of Mg layer affected the spin conduction property. © 2013 The Japan Institute of Metals and Materials.

  45. Non-local and Local Spin Signals in a Lateral Spin Transport Device with Schottky Tunnel Junctions 査読有り

    T. Saito, N. Tezuka, M. Matsuura, S. Sugimoto

    IEEE Trans.Magn. 40 (7) 0-0 2013年

    DOI: 10.1109/TMAG.2013.2248053  

  46. Si基板上への(001)配向MgO薄膜の作製 査読有り

    小野寺学史, 吉田昌弘, 手束展規, 杉本諭, 斉藤好昭

    日本金属学会誌 77 (3) 89-93 2013年

    DOI: 10.2320/jinstmet.77.89  

  47. Si上に作製したCo2FeAl0.5Si0.5フルホイスラー合金薄膜の結晶構造とスピン伝導特性 査読有り

    吉田昌弘, 小野寺学史, 手束展規, 杉本諭, 斉藤好昭

    日本金属学会誌 77 (3) 85-88 2013年

    DOI: 10.2320/jinstmet.77.85  

  48. Magnetic properties of mnbi fine particles fabricated using hydrogen plasma metal reaction 査読有り

    Keita Isogai, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    Materials Transactions 54 (9) 1673-1677 2013年

    DOI: 10.2320/matertrans.MAW201306  

    ISSN:1345-9678

    詳細を見る 詳細を閉じる

    Fine particles of MnBi were prepared by the hydrogen plasma metal reaction method and their magnetic properties were investigated. The particle size of the as-prepared MnBi particles was 70950nm with a median diameter of 269 nm. Heat treatment and ball milling with a dispersant improved the magnetic properties of the particles. The sample annealed at 330°C for 5 h in Ar then ball-milled for 10 min with a dispersant showed the largest energy product of 105 kJ̇m-3 and a saturation magnetization of 71.0Am 2̇kg-1. High coercivity of 1380 kȦm-1 was also obtained for the sample that was ball-milled for 2 h. © 2013 The Japan Institute of Light Metals.

  49. Fabrication of (001)-Oriented MgO Thin Films on Si Substrates 査読有り

    Onodera, Takashi Yoshida, Masahiro Tezuka, Nobuki Sugimoto, Satoshi Saito, Yoshiaki

    J. Jpn. Inst. Met. 77 (3) 89-93 2013年

    DOI: 10.2320/jinstmet.77.89  

  50. Microstructure and magnetic properties of Mn-Sn-N and Mn-Sn-Co-N alloys 査読有り

    Keita Isogai, Keita Shinaji, Tsuyoshi Mase, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    Materials Transactions 54 (7) 1236-1239 2013年

    DOI: 10.2320/matertrans.M2013113  

    ISSN:1345-9678

    詳細を見る 詳細を閉じる

    The microstructure and magnetic properties of Mn-Sn-N and Mn-Sn-Co-N alloys were investigated. All the samples showed low remanences, although high coercivity of 876kA/m was observed in the Mn-Sn-Co-N alloys. The substitution of Co for Mn increased coercivity. The sample with high coercivity consisted of a fine two-phase microstructure of 0.52 μm in size. © 2013 The Japan Institute of Metals and Materials.

  51. Magnetic properties of mnbi fine particles fabricated using hydrogen plasma metal reaction 査読有り

    Keita Isogai, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    Materials Transactions 54 (9) 1673-1677 2013年

    DOI: 10.2320/matertrans.MAW201306  

    ISSN:1345-9678

    詳細を見る 詳細を閉じる

    Fine particles of MnBi were prepared by the hydrogen plasma metal reaction method and their magnetic properties were investigated. The particle size of the as-prepared MnBi particles was 70950nm with a median diameter of 269 nm. Heat treatment and ball milling with a dispersant improved the magnetic properties of the particles. The sample annealed at 330°C for 5 h in Ar then ball-milled for 10 min with a dispersant showed the largest energy product of 105 kJ̇m-3 and a saturation magnetization of 71.0Am 2̇kg-1. High coercivity of 1380 kȦm-1 was also obtained for the sample that was ball-milled for 2 h. © 2013 The Japan Institute of Light Metals.

  52. Fabrication of (001)-Oriented MgO Thin Films on Si Substrates 査読有り

    Takashi Onodera, Masahiro Yoshida, Nobuki Tezuka, Satoshi Sugimoto, Yoshiaki Saito

    JOURNAL OF THE JAPAN INSTITUTE OF METALS 77 (3) 89-93 2013年

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/jinstmet.77.89  

    ISSN:0021-4876

    eISSN:1880-6880

    詳細を見る 詳細を閉じる

    We investigated the structural property of MgO thin films on Si(001) substrates by molecular beam epitaxy in order to obtain (001)-oriented MgO barrier for high spin polarization on Si substrate. The MgO layer deposited at 200 degrees C and deposition rate of 0.30 nm/min grew with (001)-orientation on Si(001) substrate. The (001)-orientation and crystallization of the MgO layer were enhanced by insertion of Mg layer into interface between Si substrate and MgO layer. It is considered that the Mg layer prevented oxidation of Si at interface and functioned as buffer layer.

  53. Microstructure and magnetic properties of Mn-Sn-N and Mn-Sn-Co-N alloys 査読有り

    Keita Isogai, Keita Shinaji, Tsuyoshi Mase, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    Materials Transactions 54 (7) 1236-1239 2013年

    DOI: 10.2320/matertrans.M2013113  

    ISSN:1345-9678

    詳細を見る 詳細を閉じる

    The microstructure and magnetic properties of Mn-Sn-N and Mn-Sn-Co-N alloys were investigated. All the samples showed low remanences, although high coercivity of 876kA/m was observed in the Mn-Sn-Co-N alloys. The substitution of Co for Mn increased coercivity. The sample with high coercivity consisted of a fine two-phase microstructure of 0.52 μm in size. © 2013 The Japan Institute of Metals and Materials.

  54. Spin-Based MOSFETs for Logic and Memory Applications and Spin Accumulation Signals in CoFe/Tunnel Barrier/SOI Devices 査読有り

    Yoshiaki Saito, Mizue Ishikawa, Tomoaki Inokuchi, Hideyuki Sugiyama, Tetsufumi Tanamoto, Kohei Hamaya, Nobuki Tezuka

    IEEE TRANSACTIONS ON MAGNETICS 48 (11) 2739-2745 2012年11月

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

    DOI: 10.1109/TMAG.2012.2202277  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    New innovative ferromagnetic source/drain technologies on Si for next-generation-transistor applications are researched and developed using CoFe/AlOx n(+)-Si and CoFe/MgO n(+)-Si junctions. As evidence of the spin accumulation in the n(+)-Si conduction channels, nonlocal spin signals and four-terminal nonlocal-Hanle signals are presented for CoFe/MgO/SOI devices. The spin diffusion times determined by four-terminal nonlocal-Hanle signals are consistent with those observed in three-terminal Hanle signals. The relatively long spin diffusion time of tau(s) = 1.4 nsec and relatively large spin polarization at room temperature for CoFe/MgO/SOI devices were observed, when fitting to the existing diffusion model for spin injection and accumulation. We have observed the marked enhancement of the absolute value of three-terminal voltage changes via Hanle-type spin precessions (vertical bar Delta V vertical bar) as a function of interface resistance in the temperature range between 20 K and 300 K. We also have observed the asymmetric bias voltage dependence on Delta V. In terms of the reason of marked enhancement of vertical bar Delta V vertical bar as a function of interface resistance, the spin absorption into ferromagnet would be most effective. For the explanation of the asymmetric bias voltage dependence, we should take into account two additional possible origins. Moreover, we succeed in decreasing the interface resistance for CoFe/MgO/n(+)-Si junctions down to 36 Omega mu m(2) by using evaporation method for MgO deposition.

  55. New materials research for high spin polarized current 招待有り 査読有り

    Nobuki Tezuka

    Journal of Magnetism and Magnetic Materials 324 (21) 3588-3592 2012年10月

    DOI: 10.1016/j.jmmm.2012.02.097  

    ISSN:0304-8853

    詳細を見る 詳細を閉じる

    The author reports here a thorough investigation of structural and magnetic properties of Co 2FeAl 0.5Si 0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co 2FeAl 0.5Si 0.5 electrodes, spin injection into GaAs semiconductor from Co 2FeAl 0.5Si 0.5, and spin filtering phenomena for junctions with CoFe 2O 4 ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co 2FeAl 0.5Si 0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co 2FeAl 0.5Si 0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co 2FeAl 0.5Si 0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of -124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of -124% corresponds to the spin polarization of -0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co 2FeAl 0.5Si 0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K. © 2012 Elsevier B.V.

  56. New materials research for high spin polarized current 招待有り 査読有り

    Nobuki Tezuka

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 324 (21) 3588-3592 2012年10月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2012.02.097  

    ISSN:0304-8853

    eISSN:1873-4766

    詳細を見る 詳細を閉じる

    The author reports here a thorough investigation of structural and magnetic properties of Co2FeAl0.5Si0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co2FeAl0.5Si0.5 electrodes, spin injection into GaAs semiconductor from Co2FeAl0.5Si0.5, and spin filtering phenomena for junctions with CoFe2O4 ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co2FeAl0.5Si0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co2FeAl0.5Si0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co2FeAl0.5Si0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of -124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of -124% corresponds to the spin polarization of -0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co2FeAl0.5Si0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K. (C) 2012 Elsevier B.V. All rights reserved.

  57. Tunnel magnetoresistance effect in magnetic tunnel junctions with epitaxial Co 2FeAl 0.5Si 0.5 Heusler electrodes on MgO (110) single substrates 査読有り

    N. Tezuka, F. Mitsuhashi, S. Sugimoto

    Journal of Applied Physics 111 (7) 07C718 2012年4月1日

    DOI: 10.1063/1.3678586  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Tunnel magnetoresistance effect has been investigated for magnetic tunnel junctions with Co 2FeAl 0.5Si 0.5 Heusler electrodes on a Cr-bufferd MgO (110) substrate. The grown Co 2FeAl 0.5Si 0.5 has L2 1 structure for annealing above 500°C. The TMR ratio of 73 at room temperature and 103 at 5 K were obtained for a junction consists of MgO(110) substrate/Cr/Co 2FeAl 0.5Si 0.5/Al-oxide/Co 75Fe 25/IrMn/Ta. The tunnel magnetoresistance ratio obtained in this study is almost the same as that estimated by using magnetic tunnel junction with the same kind of Co 2FeAl 0.5Si 0.5 electrode on a Cr-bufferd MgO (001) substrate. Smaller temperature dependence of magnetoresistance ratio was also found for the junctions on Cr-bufferd MgO(110) substrates. © 2012 American Institute of Physics.

  58. Spin injection and detection between CoFe/AlOx junctions and SOI investigated by Hanle effect measurements 査読有り

    Tomoaki Inokuchi, Mizue Ishikawa, Hideyuki Sugiyama, Yoshiaki Saito, Nobuki Tezuka

    JOURNAL OF APPLIED PHYSICS 111 (7) 07C316 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3677930  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Spin injection and detection properties in Co50Fe50/AlOx/SOI (Si on insulator) junctions were investigated by using Hanle effect measurements up to room temperature. Cross-sectional transmission electron microscope images and Fourier transform images of the Co50Fe50/AlOx/SOI junction, fabricated by using appropriate oxidation condition, indicate the AlOx layer became single-crystal-like and spin injection and detection were realized at room temperature. In contrast, in junction fabricated by using excess oxidation condition, AlOx layer became poly-crystal-like and spin injection was not realized though spin injection was realized below 150 K. These results indicate that appropriate oxidation is essential to fabricate AlOx tunnel barrier with good crystallinity and realize spin injection and detection at room temperature. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677930]

  59. Microstructure evaluation for Dy-free Nd-Fe-B sintered magnets with high coercivity 査読有り

    R. Goto, M. Matsuura, S. Sugimoto, N. Tezuka, Y. Une, M. Sagawa

    JOURNAL OF APPLIED PHYSICS 111 (7) 07A739 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3680190  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Nd-Fe-B sintered magnets are used for motors of hybrid or electric vehicles due to their high energy products. Dy is added to Nd-Fe-B sintered magnets to work in a high temperature environment. Although the addition of Dy decreases the magnetization of Nd-Fe-B magnets, it increases coercivity; a decrease in the amount of Dy is strongly required. Recently, Nd-Fe-B sintered magnets with a grain size of 1 mu m achieved high coercivity of similar to 20 kOe without the addition of Dy or other heavy rare earth elements. In this paper, the microstructure of their magnets was observed and compared to magnets with a grain size of similar to 3 mu m. The coercivity of magnets consisting of larger particles was 17 kOe. Microstructures were observed by the scanning electron microscope and the shapes of grains and the distribution of the Nd-rich phase were evaluated. The observation was promoted in two directions. One direction is the plane perpendicular to the magnetically aligned direction (c plane side) and the other is the side parallel to the magnetically aligned direction (c axis side). For magnets consisting of smaller particles, the shapes of grains are isotropic for the c plane side and elongated for the c axis side. The angle of minor axis prefers to be parallel to magnetically aligned direction. The distribution of the Nd-rich phase for magnets was also evaluated for both magnets. The distribution of the Nd-rich phase at triple junctions for the magnets with smaller particles becomes homogeneous compared to that for magnets with larger particles. It is considered that Dy-free magnets with high coercivity were realized by the achievement of homogeneous distribution of Nd-rich phase besides decreasing grain size. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3680190]

  60. Temperature and Bias Voltage Dependencies of Spin Injection Signals for CO2FeAl0.5Si0.5/n-GaAs Schottky Tunnel Junction 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 53 (4) 641-644 2012年4月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW201113  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    We investigated the temperature and bias voltage dependencies of spin injection signals for Co2FeAl0.5Si0.5 (CFAS)/n-GaAs schottky tunnel junction. Clear voltage change was observed at 10 K for the junction by 3 Terminal Hanle measurements. The maximum voltage change, Delta V-MAX, was decreased with increasing temperature and observed up to 100 K. The estimated spin relaxation time, tau, was 290 ps at 10 K and was also decreased with increasing temperature. In addition, temperature dependency of tau was lower than that of Delta V-MAX. The Delta V-MAX was increased with increasing bias voltage, and the sign of Delta V-MAX was reversed by opposite bias voltage direction. Moreover, bias dependency of Delta V-MAX became insensitive with increasing temperature. [doi:10.2320/matertrans.MBW201113]

  61. Spin injection and detection between CoFe/AlOx junctions and SOI investigated by Hanle effect measurements 査読有り

    Tomoaki Inokuchi, Mizue Ishikawa, Hideyuki Sugiyama, Yoshiaki Saito, Nobuki Tezuka

    JOURNAL OF APPLIED PHYSICS 111 (7) 07C316 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3677930  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Spin injection and detection properties in Co50Fe50/AlOx/SOI (Si on insulator) junctions were investigated by using Hanle effect measurements up to room temperature. Cross-sectional transmission electron microscope images and Fourier transform images of the Co50Fe50/AlOx/SOI junction, fabricated by using appropriate oxidation condition, indicate the AlOx layer became single-crystal-like and spin injection and detection were realized at room temperature. In contrast, in junction fabricated by using excess oxidation condition, AlOx layer became poly-crystal-like and spin injection was not realized though spin injection was realized below 150 K. These results indicate that appropriate oxidation is essential to fabricate AlOx tunnel barrier with good crystallinity and realize spin injection and detection at room temperature. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677930]

  62. Temperature and Bias Voltage Dependencies of Spin Injection Signals for CO2FeAl0.5Si0.5/n-GaAs Schottky Tunnel Junction 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 53 (4) 641-644 2012年4月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW201113  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    We investigated the temperature and bias voltage dependencies of spin injection signals for Co2FeAl0.5Si0.5 (CFAS)/n-GaAs schottky tunnel junction. Clear voltage change was observed at 10 K for the junction by 3 Terminal Hanle measurements. The maximum voltage change, Delta V-MAX, was decreased with increasing temperature and observed up to 100 K. The estimated spin relaxation time, tau, was 290 ps at 10 K and was also decreased with increasing temperature. In addition, temperature dependency of tau was lower than that of Delta V-MAX. The Delta V-MAX was increased with increasing bias voltage, and the sign of Delta V-MAX was reversed by opposite bias voltage direction. Moreover, bias dependency of Delta V-MAX became insensitive with increasing temperature. [doi:10.2320/matertrans.MBW201113]

  63. Tunnel magnetoresistance effect in magnetic tunnel junctions with epitaxial Co 2FeAl 0.5Si 0.5 Heusler electrodes on MgO (110) single substrates 査読有り

    N. Tezuka, F. Mitsuhashi, S. Sugimoto

    Journal of Applied Physics 111 (7) 07C718 2012年4月1日

    DOI: 10.1063/1.3678586  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Tunnel magnetoresistance effect has been investigated for magnetic tunnel junctions with Co 2FeAl 0.5Si 0.5 Heusler electrodes on a Cr-bufferd MgO (110) substrate. The grown Co 2FeAl 0.5Si 0.5 has L2 1 structure for annealing above 500°C. The TMR ratio of 73 at room temperature and 103 at 5 K were obtained for a junction consists of MgO(110) substrate/Cr/Co 2FeAl 0.5Si 0.5/Al-oxide/Co 75Fe 25/IrMn/Ta. The tunnel magnetoresistance ratio obtained in this study is almost the same as that estimated by using magnetic tunnel junction with the same kind of Co 2FeAl 0.5Si 0.5 electrode on a Cr-bufferd MgO (001) substrate. Smaller temperature dependence of magnetoresistance ratio was also found for the junctions on Cr-bufferd MgO(110) substrates. © 2012 American Institute of Physics.

  64. Magnetic and microwave absorption properties of polymer composites with amorphous Fe-B/Ni-Zn ferrite nanoparticles 査読有り

    Kazuaki Shimba, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS 177 (2) 251-256 2012年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.mseb.2011.12.002  

    ISSN:0921-5107

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    In this study, polymer composites containing amorphous Fe-B submicrometer particles and Ni-Zn ferrite nanoparticles were fabricated. A polymer composite of mixed particles showed high permeability mu'(r) = 13.7 at 0.5 GHz and mu ''(r) = 8.3 at 1.2 GHz. In addition, this composite exhibited good microwave absorption properties (R.L. < -20 dB) in the frequency range of 0.65-1.12 GHz for absorber thickness of 2.38-4.06 mm. It is concluded that this polymer composite can be used for fabricating microwave absorbers in the UHF range, and would result in thinner microwave absorbers than any other microwave absorbers reported thus far. (C) 2011 Elsevier B.V. All rights reserved.

  65. アモルファスFe-B 粒子樹脂複合体の電磁波吸収特性 査読有り

    結城翔三, 榛葉和晃, 手束展規, 杉本諭

    日本金属学会誌 76 (4) 278 2012年

    DOI: 10.2320/jinstmet.76.278  

  66. Nd-Fe-B薄膜におけるNd2Fe14B/Nd-Rich界面組織と保磁力 査読有り

    松浦昌志, 後藤龍太, 手束展規, 杉本諭

    日本金属学会誌 76 (1) 65 2012年

    DOI: 10.2320/jinstmet.76.65  

  67. Correlation between symmetry-selective transport and spin-dependent resonant tunneling in fully epitaxial Cr/ultrathin-Fe/MgO/Fe(001) magnetic tunnel junctions 査読有り

    Tomohiko Niizeki, Hiroaki Sukegawa, Seiji Mitani, Nobuki Tezuka, Koichiro Inomata

    APPLIED PHYSICS LETTERS 99 (18) 182508 2011年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3647578  

    ISSN:0003-6951

    eISSN:1077-3118

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    Spin-dependent resonant tunneling was investigated in fully epitaxial Cr(001)/ultrathin Fe(001)/MgO(001)/Fe(001) pseudo double-barrier magnetic tunnel junctions (MTJs) by varying structural coherence of the MgO barrier through postdeposition annealing and Mg layer insertion. It was clearly demonstrated that not only the flatness of the Fe quantum-well layer, but also the structural coherence of the MgO barrier caused the appearance of sharp resonant conductance peaks which were not obtained for spin-dependent resonant tunneling in amorphous AlO-barrier MTJs. The symmetry-selective transport via MgO barrier plays a crucial role for the resonant tunneling as well as large tunneling magnetoresistance. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3647578]

  68. Transmission Electron Microscopy Study on Nd-Rich Phase at the Surface of Nd2Fe14B Phase in Nd-Fe-B Films 査読有り

    Masashi Matsuura, Ryota Goto, Nobuki Tezuka, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 47 (10) 3273-3275 2011年10月

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

    DOI: 10.1109/TMAG.2011.2148111  

    ISSN:0018-9464

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    This study provides the abundance ratio of Nd(-O) phases at the interface of Nd2Fe14B/Nd(-O) in Nd-Fe-B films with different coercivity values. The crystal structure and morphology of the Nd2Fe14B/Nd(-O) interface were investigated by transmission electron microscopy. In the Nd-Fe-B film annealed at 350 degrees C, the coercivity of which decreases to around 20% of the value of as-deposited film, the hcp Nd2O3 phase are existed dominantly at the surface of Nd2Fe14B phase with c-plane and non-c-plane. (In this study, the planes of Nd2Fe14B with the c-axis perpendicular or non-perpendicular to the interface are described as "c-plane" and "non-c-plane", respectively.) On the contrary, C-Nd2O3 and amorphous phases, which were metastable phases, existed dominantly in the film after annealing at 650 degrees C, the coercivity of which recovers to the same level of as-deposited film. The abundance ratio of the metastable phases tends to be higher at the surface of non-c-plane than at the surface of c-plane of Nd2Fe14B phase.

  69. Electrical Transport Properties and Spin Injection in Co2FeAl0.5Si0.5/GaAs Junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 47 (10) 2447-2450 2011年10月

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

    DOI: 10.1109/TMAG.2011.2153189  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    We investigated the electrical transport properties in Co2FeAl0.5Si0.5 (CFAS)/GaAs junctions. From current density-voltage characteristics, the formation of a schottky tunnel barrier in the CFAS/GaAs interface was indicated. Moreover, junction resistance of 2 x 10(-9) Omega . m(2) which is adequate for high magnetoresistance ratio attributable to high spin injection efficiency was obtained. Comparing the bias dependencies of conductance with samples, which CFAS ordering is lower, indicated that L2(1) ordered CFAS contributes to electrical transport. Finally, the spin injection signal was observed with 3-terminal Hanle measurement, and spin relaxation time was estimated to be 380 ps at 5 K.

  70. Electrical Transport Properties and Spin Injection in Co2FeAl0.5Si0.5/GaAs Junctions 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 47 (10) 2447-2450 2011年10月

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

    DOI: 10.1109/TMAG.2011.2153189  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    We investigated the electrical transport properties in Co2FeAl0.5Si0.5 (CFAS)/GaAs junctions. From current density-voltage characteristics, the formation of a schottky tunnel barrier in the CFAS/GaAs interface was indicated. Moreover, junction resistance of 2 x 10(-9) Omega . m(2) which is adequate for high magnetoresistance ratio attributable to high spin injection efficiency was obtained. Comparing the bias dependencies of conductance with samples, which CFAS ordering is lower, indicated that L2(1) ordered CFAS contributes to electrical transport. Finally, the spin injection signal was observed with 3-terminal Hanle measurement, and spin relaxation time was estimated to be 380 ps at 5 K.

  71. Magnetoresistance effect of tunnel junctions using Co-2(Ti, Mn)Z (Z = Al, Si) Heusler alloys 査読有り

    A. Sasaki, N. Tezuka, L. Jiang, S. Sugimoto

    JOURNAL OF APPLIED PHYSICS 109 (7) 07C736 2011年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3556778  

    ISSN:0021-8979

    eISSN:1089-7550

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    We investigated postannealing temperature dependence of the structural and magnetic properties of Co2Ti0.5Mn0.5Al and Co2Ti0.5Mn0.5Si films. It was observed that the Co2Ti0.5Mn0.5Al film formed an ordered L2(1) structure and an ordered B2 structure after postannealing at above 873 K and below 773 K, respectively. The Co2Ti0.5Mn0.5Si film deposited with substrate heating at above 473 K formed an ordered L2(1) structure. The obtained magnetoresistance ratio for a junction using an L2(1) ordered Co2Ti0.5Mn0.5Si electrode was 12.5% at room temperature (RT). The estimated spin polarization of the Co2Ti0.5Mn0.5Si film was 0.14 at RT. The magnetoresistance ratios of a junction using a B2 ordered Co2Ti0.5Mn0.5Al electrode were 65.8% at RT and 128.4% at 7 K. The estimated spin polarizations of the Co2Ti0.5Mn0.5Al film were 0.56 at RT and 0.78 at 7 K. (C) 2011 American Institute of Physics. [doi:10.1063/1.3556778]

  72. Microwave Absorption Properties of Polymer Modified Ni-Zn Ferrite Nanoparticles 査読有り

    Kazuaki Shimba, Kiyotaka Furuta, Nobuyuki Morimoto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 52 (4) 740-745 2011年4月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW201013  

    ISSN:1345-9678

    eISSN:1347-5320

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    Polymer composites of magnetic particles are widely used as microwave absorbers. An effective method for obtaining thinner microwave absorbers for device design is increasing the volume fraction of magnetic nanoparticles by enhancing the permeability of composites. In this study, composites were prepared using Ni-Zn ferrite nanoparticles surface-modified with 4-META (4-methacryloylioxyethyl trimellitate anhydride) and cross-linked with PEG-4SH (pentaerythritol tetra-polyethylene glycol ether with four thiol-modified terminals). These composites have a high volume fraction of nanoparticles (up to 72 vol%) and permeability (mu '' r(max)= 5.9). In addition, the prepared composites showed good microwave absorption properties (R.L. < -20 dB) with a smaller matching thickness than conventional microwave absorber using spinel-type ferrite. [doi:10.2320/matertrans.MBW201013]

  73. Magnetoresistance effect of tunnel junctions using Co-2(Ti, Mn)Z (Z = Al, Si) Heusler alloys 査読有り

    A. Sasaki, N. Tezuka, L. Jiang, S. Sugimoto

    JOURNAL OF APPLIED PHYSICS 109 (7) 07C736 2011年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3556778  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We investigated postannealing temperature dependence of the structural and magnetic properties of Co2Ti0.5Mn0.5Al and Co2Ti0.5Mn0.5Si films. It was observed that the Co2Ti0.5Mn0.5Al film formed an ordered L2(1) structure and an ordered B2 structure after postannealing at above 873 K and below 773 K, respectively. The Co2Ti0.5Mn0.5Si film deposited with substrate heating at above 473 K formed an ordered L2(1) structure. The obtained magnetoresistance ratio for a junction using an L2(1) ordered Co2Ti0.5Mn0.5Si electrode was 12.5% at room temperature (RT). The estimated spin polarization of the Co2Ti0.5Mn0.5Si film was 0.14 at RT. The magnetoresistance ratios of a junction using a B2 ordered Co2Ti0.5Mn0.5Al electrode were 65.8% at RT and 128.4% at 7 K. The estimated spin polarizations of the Co2Ti0.5Mn0.5Al film were 0.56 at RT and 0.78 at 7 K. (C) 2011 American Institute of Physics. [doi:10.1063/1.3556778]

  74. Magnetic Properties of Nanoparticle-Polymer Composites Prepared Using Surface Modification and Cross-Linking Reaction 査読有り

    Kazuaki Shimba, Kiyotaka Furuta, Nobuyuki Morimoto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 52 (3) 486-490 2011年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201020  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    Polymer composites of magnetic particles are widely used as microwave absorbers. An effective method for obtaining thinner microwave absorbers for device mounting is to increase the volume fraction of magnetic nanoparticles within the composites such that the permeability is enhanced. In this study, composites were prepared using magnetite nanoparticles surface-modified with 4-META (4-methacryloylioxyethyl trimellitate anhydride) and cross-linked with PEG-4SH (pentaerythritol tetra-polyethylene glycol ether with four thiol-modified terminals). These composites have a higher volume fraction of nanoparticles (up to 62 vol%) and higher permeability than conventional epoxy resin composites. In addition, the prepared composites showed good microwave absorption properties (R.L. < -20 dB) with a smaller matching thickness (d = 8.0 mm) than the epoxy resin composites (d = 9.0 mm). [doi:10.2320/matertrans.MAW201020]

  75. Structural and Magnetic Properties of Co2FeAl0.5Si0.5 Full-Heusler Alloy Thin Films on GaAs Substrates 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 52 (3) 370-373 2011年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW201004  

    ISSN:1345-9678

    eISSN:1347-5320

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    We investigated the structural and magnetic properties of Co2FeAl0.5Si0.5 (CFAS) thin films on GaAs substrates. The CFAS thin films grew epitaxially on GaAs with CFAS (100)[100] parallel to GaAs (100)[100] relation and formed an ordered L2(1) structure with substrate heating deposition at T-SUB = 300 degrees C, 400 degrees C and post annealed at T-PA = 400 degrees C. Moreover, we confirmed the no reaction between CFAS and GaAs. The CFAS thin films on GaAs showed strong uniaxial magnetic anisotropy with an easy axis of [110](CFAS) ([110]GaAs) direction and the magnetic anisotropy generally increased by decreasing the thickness of CFAS. The magnetic moment of the CFAS film deposited with substrate heating at 300 degrees C was approximately 4.8 mu(B)/f.u. at room temperature. [doi:10.2320/matertrans.MBW201004]

  76. Structural and Magnetic Properties of Co2FeAl0.5Si0.5 Full-Heusler Alloy Thin Films on GaAs Substrates 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 52 (3) 370-373 2011年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW201004  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    We investigated the structural and magnetic properties of Co2FeAl0.5Si0.5 (CFAS) thin films on GaAs substrates. The CFAS thin films grew epitaxially on GaAs with CFAS (100)[100] parallel to GaAs (100)[100] relation and formed an ordered L2(1) structure with substrate heating deposition at T-SUB = 300 degrees C, 400 degrees C and post annealed at T-PA = 400 degrees C. Moreover, we confirmed the no reaction between CFAS and GaAs. The CFAS thin films on GaAs showed strong uniaxial magnetic anisotropy with an easy axis of [110](CFAS) ([110]GaAs) direction and the magnetic anisotropy generally increased by decreasing the thickness of CFAS. The magnetic moment of the CFAS film deposited with substrate heating at 300 degrees C was approximately 4.8 mu(B)/f.u. at room temperature. [doi:10.2320/matertrans.MBW201004]

  77. Structural and Magnetic Properties of Co2FeAl0.5Si0.5 Full-Heusler Alloy Thin Films Deposited on Si Substrates by Molecular Beam Epitaxy 査読有り

    Tatsuya Saito, Ken Kano, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF THE JAPAN INSTITUTE OF METALS 75 (3) 141-145 2011年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/jinstmet.75.141  

    ISSN:0021-4876

    eISSN:1880-6880

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    We investigated the structural and magnetic properties of Co2FeAl0.5Si0.5 (CFAS) full-Heusler alloy thin films deposited on Si/SiO2/(001)-oriented MgO strucutre by molecular beam epitaxy. The MgO layer deposited at 300 degrees C grew with an enough (001)-orientation to obtain high spin polarization on Si/SiO2 substrate. The CFAS thin films on Si/SiO2/ (001)-oriented MgO structure showed only (220) peaks in XRD measurements. However, those films also showed high magnetization, same as the magnetization of L2(1)-ordered CFAS on MgO substrates. Therefore, it is considered that the CFAS thin films on Si/SiO2/(001)-oriented MgO structure have the high ordered structure.

  78. MBEによりSi基板上に成膜されたCo2FeAl0.5Si0.5薄膜の結晶構造と磁気特性 査読有り

    Tatsuya Saito, Nobuki Tezuka, Satoshi Sugimoto

    日本金属学会誌 75 (3) 141 2011年

    DOI: 10.2320/jinstmet.75.141  

  79. Spin injection and detection between CoFe/AlOx junctions and SOI investigates by Hanle effect measurements 査読有り

    TTT

    JOURNAL OF THE JAPAN INSTITUTE OF METALSfff 75 141-145 2011年

  80. Influence of Nd Oxide Phase on the Coercivity of Nd-Fe-B Thin Films 査読有り

    Masashi Matsuura, Ryota Goto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 51 (10) 1901-1904 2010年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW201019  

    ISSN:1345-9678

    eISSN:1347-5320

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    To understand the coercivity mechanism of Nd Fe B sintered magnets the microstructure of grain boundary composed of Nd2Fe14B and Nd rich phases has been studied However the influence of Nd rich phase which contains some amount of oxygen on microstructure and coercivity has not been clear In this study the influence and the interfacial microstructure between the Nd2Fe14B phase and the Nd rich phase were investigated using Nd Fe B thin films Furthermore the microstructural change of Nd oxide (Nd 0) phase was investigated using oxidized Nd thin films The coercivity (H-cJ) of the Nd Fe B thin films decreased by about 80% from the level of as deposited film (H-cJ(as depo)) after oxidation and annealing at low temperature (similar to 350 degrees C) From TEM observation of the Nd Fe B film some steps along the surface of the Nd2Fe14B phase contacting with the hcp Nd2O3 phase were observed Investigation of the microstructural change of Nd oxide phase was carried out using Nd thin films The as deposited Nd film was composed of the dhcp Nd (alpha Nd) phase and the fcc NdOx phase formed at the surface of a Nd phase after oxidation After annealing at 350 degrees C the hcp Nd2O3 phase crystallized from the fcc NdOx phase and it resulted in large roughness at the boundary with the alpha Nd phase From the results described above the crystallization of hcp Nd2O3 phase causes damage at the surface of Nd2Fe14B phase during the annealing at low temperature which results in the decrease of coercivity [doi 10 2320/matertrans MAW201019]

  81. 溶融硝酸鉄の還元による窒化鉄Fe16N2 微粒子の作製 査読有り

    榛葉和晃, 手束展規, 杉本 諭

    日本金属学会誌 74 (3) 209-213 2010年3月

    DOI: 10.2320/jinstmet.74.209  

  82. Coフェライト複合ナノ粒子の作製 査読有り

    深町七奈, 手束展規, 杉本諭

    日本金属学会誌 74 (6) 2010年

    DOI: 10.2320/jinstmet.74.345  

  83. 表面修飾された磁性ナノ粒子によるナノコンポジット粉末の作製 査読有り

    榛葉和晃, 深町七奈, 手束展規, 杉本諭

    電気学会研究会資料 MAGマグネティックス研究会 71 2010年

  84. Microstructural Evaluation of Nd-Fe-B Jet-Milled Powders 査読有り

    Takashi Hattori, Hiroki Ishihara, Satoshi Sugimoto, Ryota Goto, Nobuki Tezuka, Yasuhiro Une, Masato Sagawa

    MATERIALS TRANSACTIONS 50 (10) 2347-2350 2009年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW200915  

    ISSN:1345-9678

    eISSN:1347-5320

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    Nd-Fe-B sintered magnets have high energy products and are used for various applications. Motors of hybrid vehicles (HEVs) are one of the major applications. For usage of HEVs, Dy is added to Nd-Fe-B magnets to maintain coercivity at high temperature environment. However, due to low natural resources of Dy, Dy-free or Dy-lean Nd-Fe-B sintered magnets are strongly required. To achieve high coercivity, it is necessary that microstructure of sintered magnets is consisted of both fine main phase particles and homogeneously distributed Nd-rich phases around the main phase. In this study, the microstructure of Nd-Fe-B jet-milled powders and the distribution of the Nd-rich phase were investigated. The distribution of the Nd-rich phase was evaluated by the ratio of grains which contain the Nd-rich phase. With decreasing size of the jet-milled Nd-Fe-B powder, the Nd-rich phase tends to aggregate and its distribution becomes inhomogeneous. The powder size of Nd-Fe-B jet-milled powder is much smaller than the average lamella interval of strip cast alloys. [doi:10.2320/matertrans.MAW200915]

  85. Co2Ti0.5Mn0.5Alフルホイスラー合金薄膜を用いた強磁性トンネル接合の磁気抵抗効果 査読有り

    佐々木陽光, 手束展規, 杉本 諭, 大久保亮成, 梅津理恵, 貝沼亮介

    日本金属学会誌 73 (9) 2009年9月

    DOI: 10.2320/jinstmet.73.670  

  86. Influences of Oxidation State of Nd-Rich Phase on the Coercivity of Nd-Fe-B/Nd Thin Films 査読有り

    Masashi Matsuura, Togo Fukada, Ryota Goto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 50 (9) 2139-2142 2009年9月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MAW200913  

    ISSN:1345-9678

    eISSN:1347-5320

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    The Nd-rich phase of Nd-Fe-B sintered magnets, which contains some amount of oxygen, plays an important role for generating coercivity. However, the influence of interfacial microstructure between Nd2Fe14B and Nd-rich phases has not been clear. In this study, Nd2Fe14B/Nd(-O) interface was prepared by thin film technique and the influence of oxidation state of Nd-rich phase on the coercivity was investigated. A Nd-Fe-B layer was deposited by ultra high vacuum (UHV) magnetron sputtering, and the film was oxidized under low vacuum condition (low oxidation state) or At atmosphere (high oxidation state). A Nd layer was deposited on the oxidized Nd-Fe-B layer, and the film was annealed at 250-650 degrees C for 60 min. The coercivity of films oxidized in low oxidation state was recovered by annealing at 250-650 degrees C, and an amorphous phase was observed at the interface between Nd2Fe14B and hcp Nd2O3 (+ fee NdOx) phases in the film annealed at 350 degrees C. On the other hand, the coercivity of films oxidized in high oxidation state was lower than that of films oxidized in low oxidation state, and it decreased more about 20% by annealing at 250-350 degrees C. However, an amorphous phase was not observed at the interface of these films. After annealing above 550 degrees C, the coercivity of films oxidized in both low and high oxidation state recovered drastically to the almost same value of as-deposited film. From the SAD patterns of TEM observation, a metastable C-Nd2O3 phase was present in the Nd-rich phase of these films. In addition, it is known that the wettability of Nd-rich phase improves at temperatures around 550 degrees C. Therefore, it is considered that the increase of coercivity is related to the improvement of fluidity of Nd-rich phase or the existence of C-Nd2O3 phase. [doi:10.2320/matertrans.MAW200913]

  87. Effect of Cu Addition on the Phase Equilibria in Nd-Fe-B Sintered Magnets 査読有り

    Shota Nishio, Satoshi Sugimoto, Ryota Goto, Masashi Matsuura, Nobuki Tezuka

    MATERIALS TRANSACTIONS 50 (4) 723-726 2009年4月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW200824  

    ISSN:1345-9678

    eISSN:1347-5320

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    Nd-Fe-B sintered magnets show high energy products and have started to be used for motors of hybrid electric vehicles (HE-Vs). For the use of the magnets, the understanding of the coercivity mechanism is required for obtaining, high coercivity. The Nd-rich phase in Nd-Fe-B sintered magnets plays an important role in cleaning the surface of Nd2Fe14B grains for decreasing the number of nucleation sites of reverse domains. which leads to high coercivity. In this study. the phase equilibria including oxygen in Nd-Fe-B sintered magnets are discussed in view of the wettability between Nd-rich phase and Nd2Fe14B phase. It is considered that Cu addition decrease,, the free energy of Nd-rich liquid phase, which leads to the shift of liquidus line of Nd-O system to lower temperature and the increase in solubility limit of oxygen. Due to improvement of wettability and increase in solubility limit. Cu-added Nd-rich liquid spread easily and form homogeneous liquid phase during the sintering process. These phenomena enhance cleaning effect of Nd-rich phase and contribute to the increase in coercivity of Nd-Fe-B sintered magnets. [doi: 10.2320/matertrans.MBW200824]

  88. Interfacial state and magnetic properties of Nd-Fe-B/Nd thin films 査読有り

    Masashi Matsuura, Satoshi Sugimoto, Ryota Goto, Nobuki Tezuka

    JOURNAL OF APPLIED PHYSICS 105 (7) 07A741-1-07A741-3 2009年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3076050  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Nd-Fe-B/Nd(-O) interfaces were prepared by thin film technique for the investigation of relationship between interfacial state and coercivity. A Nd-Fe-B layer was deposited by UHV magnetron sputtering and the film was oxidized under low vacuum conditions. On the oxidized Nd-Fe-B layer, a Nd layer was deposited and the film was annealed at 250-650 degrees C. The coercivity of Nd-Fe-B layer decreased after the oxidation. However, it recovered after the deposition of Nd layer and the annealing at 350 degrees C. High-resolution transmission electron microscopy (HRTEM) observations revealed that an fcc NdO phase forms after the oxidation and an amorphous phase exists along the interface between Nd(2)Fe(14)B and Nd(2)O(3) phases after annealing at 350 degrees C. Therefore, the recovery of coercivity is related to the amorphous phase, which is considered to be formed by the transformation from NdO to Nd(2)O(3) and alpha-Nd, and the release of strain at the interface. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3076050]

  89. The Magnetoresistance of Fe/MgO/GaAs/MgO/Fe Junctions 査読有り

    Fuminori Mitsuhash, Nobuki Tezuka, Satoshi Sugimoto

    JOURNAL OF THE JAPAN INSTITUTE OF METALS 73 (4) 251-254 2009年4月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/jinstmet.73.251  

    ISSN:0021-4876

    eISSN:1880-6880

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    We investigated the structure and magnetoresistance effect for the Fe/MgO/GaAs/MgO/Fe junctions. The junctions were deposited on MgO(001) single crystal substrate by Molecular Beam Epitaxy. RHEED patterns and XRD pole profiles reveal that bottom electrodes, Fe, and inter layers, n-GaAs, grow epitaxially. While RHEED patterns reveal that upper electrodes, Fe, grow in a polycrystal form. The junctions exhibit magnetoresistance ratio of 3.2% at room temperature. The magnetoresistance curves correspond to the magnetization alignment between the bottom and the upper Fe electrodes. These results indicate that the magnetoresistance effect originates from spin injection from Fe to GaAs through MgO barriers.

  90. Improved tunnel magnetoresistance of magnetic tunnel junctions with 査読有り

    N. Tezuka, N. Ikeda, F. Mitsuhashi, S. Sugimoto

    APPLIED PHYSICS LETTERS 94 162504-1-162504-3 2009年4月

    DOI: 10.1063/1.3116717  

  91. Microstructural Evaluation of Nd-Fe-B Strip Cast Alloys 査読有り

    Takashi Hattori, Nana Fukamachi, Ryota Goto, Nobuki Tezuka, Satoshi Sugimoto

    MATERIALS TRANSACTIONS 50 (3) 479-482 2009年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.MBW200821  

    ISSN:1345-9678

    eISSN:1347-5320

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    In this investigation, we evaluated the microstructure of SC alloys using SEM, TEM and XRD. The composition of SC alloys was Nd14.4Fe79.6B6.0 and Nd10.4Dy3.5Fe80B6.1, and the SC alloys show petal-shape or dendritic structure at the wheel surface or the free surface, respectively. Grain size distribution is broad at the wheel surface and the microstructure is changed at the distance of around 50 mu m from the wheel surface. XRD analyses are consistent with the results. Average interval of R-rich (R: rare earth) lamella structure in Nd10.4Dy3.5Fe80B6.1 and Nd14.4Fe79.6B6.0 SC alloys are 3.9 mu m and 3.7 mu m, respectively. [doi: 10.2320/matertrans.MBW200821]

  92. Tunnel magnetoresistance for magnetic tunnel junctions with Co2FeAl0.5Si0.5 査読有り

    N. Tezuka, N. Ikeda, F. Mitsuhashi, S. Sugimoto

    JOURNAL OF APPLIED PHYSICS 105 07C925-1-07C925-3 2009年

    DOI: 10.1063/1.3072448  

  93. Wettability and Interfacial Microstructure Between Nd2Fe14B and Nd-Rich Phases in Nd-Fe-B Alloys 査読有り

    Ryota Goto, Shota Nishio, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    IEEE TRANSACTIONS ON MAGNETICS 44 (11) 4232-4234 2008年11月

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

    DOI: 10.1109/TMAG.2008.2001544  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    For achievement of high coercivity in Dy-free or-lean Nd-Fe-B permanent magnet system, understanding of reaction process between Nd-Fe-B main and Nd-rich phases is required. In this work, the wettability between Nd2Fe14B and Nd-rich phases was investigated by the measurement of contact angles under isothermal heating. The activation energy for wetting was estimated by the time when the contact angle became constant and the activation energies for ternary and Cu-added Nd-rich ingots were 196.8 and 162.6 kJ/mol, respectively. Interfacial microstructure drastically changed at the temperature lower than the melting point of the Nd-rich ingots and the interface of Cu-added Nd-rich ingots became rough at lower temperature than ternary ones. It is concluded that Cu-addition is effective for the reduction of the activation energy of wetting and improves wetting behavior of Nd-rich phase.

  94. Site disorder in Co2Fe(Al,Si) Heusler alloys and its influence on junction tunnel magnetoresistance 査読有り

    K. Inomata, M. Wojcik, E. Jedryka, N. Ikeda, N. Tezuka

    PHYSICAL REVIEW B 77 (21) 214425-1-214425-9 2008年6月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.77.214425  

    ISSN:2469-9950

    eISSN:2469-9969

    詳細を見る 詳細を閉じる

    The local structures around Co atoms in Co2FeSi1-xAlx (x=0, 0.5, and 1.0) Heusler alloys have been investigated using Co-59 NMR spin-echo method and their effect on the tunneling magnetoresistance for the junctions using Co2FeSi0.5Al0.5 electrodes has been discussed. The Co-59 NMR spectra of the Heusler alloys are extremely sensitive to the site disorder and clearly distinguish among the A2, B2, and L2(1) structures providing quantitative information on the amount of disorder. The tunnel magnetoresistance for the junctions is demonstrated to be sensitive to the site disorder in Co2FeSi0.5Al0.5 electrodes.

  95. Energy barrier and reversal mechanism in Co/Pt multilayer nanodot 査読有り

    S. Okamoto, T. Kato, N. Kikuchi, O. Kitakami, N. Tezuka, S. Sugimoto

    JOURNAL OF APPLIED PHYSICS 103 (7) 07C501-1-07C501-3 2008年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2831785  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    We have studied the reversal behavior in a single nanomagnet of Co/Pt by using anomalous Hall effect measurement technique. [Co(0.6-1.4 nm)/Pt(2 nm)](3) multilayer films were lithographically patterned into single dots with the diameter of 200 nm. The magnetic anisotropy K(u) of the dots was varied from 1.3 x 10(7) to 2.6 x 10(7) erg/cc by decreasing the Co thickness. From the rectangular magnetization curve and the Stoner-Wohlfarth-type angular dependence of reversal field, the magnetization reversal of the dot was concluded to proceed by the nucleation of a reversed embryo and its immediate expansion. The energy barrier E(b)(0) for the magnetization reversal evaluated by the reversal probability experiment increased monotonically with K(u) and showed the almost same dependence on K(u) both at 300 and 100 K. These results suggest that the reversal mechanism is simply dominated by the magnetic anisotropy K(u) and is invariable in this temperature range. This behavior of E(b)(0) can be qualitatively explained by considering the nucleation of an embryo having the size of domain wall width. (c) 2008 American Institute of Physics.

  96. Magnetization reversal process and bistability of Co/Pt multilayer dot 査読有り

    N. Kikuchi, T. Kato, S. Okamoto, O. Kitakami, N. Tezuka, S. Sugimoto

    JOURNAL OF APPLIED PHYSICS 103 (7) 07C510-1-07C510-3 2008年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2838288  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Magnetization reversal process and the critical diameter d(c) for single and multidomain of Co/Pt multilayer dot were investigated by detecting anomalous Hall effect of a single dot with diameter d ranging from 100 to 1000 nm. The perpendicular anisotropy constant K(u) was varied from 1.3x10(7) to 2.6x10(7) erg/cc by changing the Co layer thickness. The dominant magnetization process for the dots with d >= 1000 nm was domain wall displacement, while nucleation of a reversed embryo governed the reversals in the dots smaller than 500 nm. The d(c) for stable single domain increases with K(u) from 150 nm to larger than 1000 nm. This behavior is mainly due to the increase of domain wall energy owing to the increase of K(u), and the d(c) coincides very well with the domain size of continuous films. (c) 2008 American Institute of Physics.

  97. Enhanced tunnel magnetoresistance due to spin dependent quantum well resonance in specific symmetry states of an ultrathin ferromagnetic electrode 査読有り

    Tomohiko Niizeki, Nobuki Tezuka, Koichiro Inomata

    PHYSICAL REVIEW LETTERS 100 (4) 047207-1-047207-4 2008年2月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.100.047207  

    ISSN:0031-9007

    eISSN:1079-7114

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    Spin dependent quantum well resonance has been investigated in fully epitaxial magnetic tunnel junctions with Fe(001)/MgO(001)/ultrathin Fe(001)/Cr(001) structure. The dI/dV spectra clearly show the resonant peaks which shift systematically depending on the thickness of an ultrathin electrode as predicted in ab initio calculation [Zhong-Yi Lu , Phys. Rev. Lett. 94, 207210 (2005)]. The magnetotransport is strongly modulated at the same bias voltage as the resonant peaks. This control of the magnetotransport in magnetic tunnel junctions at a specific bias voltage will contribute to the development of active spintronic devices.

  98. Nd-Fe-B系合金におけるNd2Fe14B相とNd-rich相間の濡れ性 査読有り

    西尾翔太, 後藤龍太, 松浦昌志, 手束展規, 杉本 諭

    日本金属学会誌 72 (12) 1010-1014 2008年

    DOI: 10.2320/jinstmet.72.1010  

  99. Highly spin-polarized materials and devices for spintronics 査読有り

    Koichiro Inomata, Naomichi Ikeda, Nobuki Tezuka, Ryogo Goto, Satoshi Sugimoto, Marek Wojcik, Eva Jedryka

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1) 014101 2008年1月

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1088/1468-6996/9/1/014101  

    ISSN:1468-6996

    eISSN:1878-5514

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    The performance of spintronics depends on the spin polarization of the current. In this study half-metallic Co-based full-Heusler alloys and a spin filtering device (SFD) using a ferromagnetic barrier have been investigated as highly spin-polarized current sources. The multilayers were prepared by magnetron sputtering in an ultrahigh vacuum and microfabricated using photolithography and Ar ion etching. We investigated two systems of Co-based full-Heusler alloys, Co2Cr1-xFexAl(CCFA(x)) and Co2FeSi1-xAlx (CFSA(x)) and revealed the structure and magnetic and transport properties. We demonstrated giant tunnel magnetoresistance (TMR) of up to 220% at room temperature and 390% at 5K for the magnetic tunnel junctions (MTJs) using Co2FeSi0.5Al0.5(CFSA(0.5)) Heusler alloy electrodes. The 390% TMR corresponds to 0.81 spin polarization for CFSA(0.5) at 5 K. We also investigated the crystalline structure and local structure around Co atoms by x-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses, respectively, for CFSA films sputtered on a Cr-buffered MgO (001) substrate followed by post-annealing at various temperatures in an ultrahigh vacuum. The disordered structures in CFSA films were clarified by NMR measurements and the relationship between TMR and the disordered structure was discussed. We clarified that the TMR of the MTJs with CFSA(0.5) electrodes depends on the structure, and is significantly higher for L2(1) than B2 in the crystalline structure. The second part of this paper is devoted to a SFD using a ferromagnetic barrier. The Co ferrite is investigated as a ferromagnetic barrier because of its high Curie temperature and high resistivity. We demonstrate the strong spin filtering effect through an ultrathin insulating ferrimagnetic Co-ferrite barrier at a low temperature. The barrier was prepared by the surface plasma oxidization of a CoFe2 film deposited on a MgO (001) single crystal substrate, wherein the spinel structure of CoFe2O4 (CFO) and an epitaxial relationship of MgO(001)[100]/CoFe2(001)] 110]/ CFO(001)[100] were induced. A SFD consisting of CoFe2/CFO/Ta on a MgO (001) substrate exhibits the inverse TMR of -124% at 10K when the configuration of the magnetizations of CFO and CoFe2 changes from parallel to antiparallel. The inverse TMR suggests the negative spin polarization of CFO, which is consistent with the band structure of CFO obtained by first principle calculation. The -124% TMR corresponds to the spin filtering efficiency of 77% by the CFO barrier.

  100. Fabrication and characterization of Co-ferrite thin films for a ferromagnetic barrier in a spin-filtering device operating at room temperature 査読有り

    R. Goto, Y. K. Takahashi, N. Tezuka, K. Inomata, S. Sugimoto, K. Hono

    IEEE TRANSACTIONS ON MAGNETICS 43 (6) 2797-2799 2007年6月

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

    DOI: 10.1109/TMAG.2007.893696  

    ISSN:0018-9464

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    For development of a spin-filtering device with a ferromagnetic barrier, very thin Co-ferrite layers are prepared by the plasma oxidization of the CoFe2 surface deposited on MgO(001) single crystal substrates and postannealing process. Spin-filtering junctions consisting of CoFe2/(MgO/)Co-ferrite/Ta are fabricated and exhibit nonlinear J-V curves. By the insertion of a MgO layer, clear independent rotation of two magnetic moments is observed.

  101. Transmission electron microscopy of Co-2(Cr1-xFex)Al sputtered films and their magnetic tunneling junctions 査読有り

    Y. K. Takahashi, T. Ohkubo, K. Hono, S. Okamura, N. Tezuka, K. Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 313 (2) 378-382 2007年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.09.023  

    ISSN:0304-8853

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    The microstructures of Co2FeAl and Co-2(Cr0.4Fe0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co2FeAl film changed from B2 to L2(1) with increasing substrate temperature, while that of the Co-2(Cr0.4Fe0.6)Al film remained B2 up to 500 degrees C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co2FeAl and Co-2(Cr0.4Fe0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low. (c) 2006 Elsevier B.V. All rights reserved.

  102. Giant tunnel magnetoresistance at room temperature for junctions using full-heusler Co2FeAl0.5Si0.5 electrodes 査読有り

    Nobuki Tezuka, Naomichi Ikeda, Satoshi Sugimoto, Koichiro Inomata

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 (17-19) L454-L456 2007年5月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.46.L454  

    ISSN:0021-4922

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    The authors have investigated the tunnel magnetoresistance (TMR) effect of magnetic tunnel junctions (MTJs) with Co2FeAl0.5Si0.5 full-Heuster electrodes and a MgO barrier in the thickness range of 1.5-2.5 nm. A cross-sectional transmission electron micrograph showed the epitaxial growth of both the upper and lower Co2FeAl0.5Si0.5 layers and a MgO barrier and some distortion in the MgO barrier after annealing above 400 degrees C. An exponential dependence of resistance x area product on MgO barrier thickness was observed. TMR ratio was strongly affected by MgO barrier thickness, exhibiting maxima of 220% at room temperature and 390% at 5 K. The latter corresponds to the spin polarization of 0.81. It was also found that the features of this MTJ include a small asymmetry voltage and weak temperature dependence of its TMR ratio.

  103. Tunnel magnetoresistance in magnetic tunnel junctions with Co2Fe (Al, Si) full-Heusler films 査読有り

    N. Tezuka, N. Ikeda, A. Miyazaki, S. Okamura, M. Kikuchi, S. Sugimoto, K. Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 1940-1942 2007年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.10.812  

    ISSN:0304-8853

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    The magnetoresistance effect for a magnetic tunnel junction ( MTJ) with Co2FeAl0.5Si0.5 electrodes on Cr buffered MgO ( 0 0 1) substrate has been investigated. The MTJ with B2- type Co2FeAl0.5Si0.5 electrode exhibited tunnel magnetoresistance ( TMR) ratio of 76% at room temperature ( RT) and 106% at 5K, while that with L2(1) structure showed 51% and 78% at RT and 5K, respectively. For both cases, the bias voltage dependence of TMR ratio is almost the same, but only for the MTJs with a Co2FeAl0.5Si0.5 electrode annealed at 600 degrees C shows a dip around similar to 200 mV. (c) 2006 Elsevier B. V. All rights reserved.

  104. Preparation of Fe/Ni-Zn-Cu ferrite stacked films by aerosol deposition method 査読有り

    S. Sugimoto, V. Chan, M. Noguchi, N. Tezuka, K. Inomata, J. Akedo

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2) 2549-2551 2007年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2006.11.146  

    ISSN:0304-8853

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    Composite or stacked. lms composed of Fe and Ni-Zn-Cu ferrite were prepared by aerosol deposition (AD) method, and the relationship between magnetic properties and microstructure was investigated. Aiming to control the microstructure, two aerosol chambers and double nozzles, from which each powder ejected independently, were used in the AD system. With increase in the vibration frequency of Fe aerosol chamber (V-Fe) or the deposition time of Fe powder (t(Fe)), the Fe content in the. lms increased, which was resulted in the increase of saturation magnetization and permeability. The composite or stacked. lms also showed relatively high-noise suppression effect (Delta P-loss/P-in = similar to 0.58). Microstructural analyses revealed that the stacked film consisted of Fe and ferrite layers with thickness of 1 and 15 mm, respectively. (C) 2006 Elsevier B. V. All rights reserved.

  105. Coercivity and microstructure of Mn-Ni-N sintered alloys 招待有り 査読有り

    S. Sugimoto, K. Isogai, T. Hattori, H. Matsumoto, S. Yoshida, N. Tezuka

    Phys. Stat. Sol. 4 4573-4576 2007年

    DOI: 10.1002/pssc.200777401  

  106. プラズマ酸化法により作製したCoフェライト薄膜の構造と磁気特性 査読有り

    後藤龍太, 高橋有紀子, 中村新一, 手束展規, 猪俣浩一郎, 杉本諭, 宝野和博

    日本応用磁気学会誌 31 (4) 351-355 2007年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.31.351  

    ISSN:0285-0192

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    For the development of room temperature spin-filtering devices with a ferromagnetic barrier, very thin ferromagnetic barrier films were required. Co-ferrite thin films are prepared by the surface plasma oxidization of a CoFe<sub>2</sub> underlayer deposited on MgO (001) single crystal substrates. During oxidization, the substrate temperature was varied from 523 K to 673 K. The plasma oxidized CoFe<sub>2</sub> films had a spinel structure, 4-fold symmetry in the plane, and an epitaxial relationship with the CoFe<sub>2</sub> underlayer. The lattice parameter of Co-ferrite thin film was 0.828 nm, which is 1.2% less than that of bulk. The interface between the CoFe<sub>2</sub> and its oxide was relatively smooth. When the substrate temperature during plasma oxidization was lower than 623 K, magnetization of CoFe<sub>2</sub> and Co-ferrite rotated independently. XPS and MOKE measurements identified that the hard and soft phases as Co-ferrite and CoFe<sub>2</sub>, respectively. Measurements of the magnetic properties showed that the magnetization of the Co-ferrite thin films was about 1100 emu/cm<sup>3</sup>, which is 2.6 times more than that of bulk (420 emu/cm<sup>3</sup>). This phenomenon may be explained by the exchange of Co and Fe cation distribution in our Co-ferrite films.

  107. プラズマ酸化法により作製したCoフェライト薄膜の構造、磁気およびバリア特性 査読有り

    後藤龍太, 高橋有紀子, 手束展規, 猪俣浩一郎, 杉本諭, 宝野和博

    日本金属学会誌 2007年

    DOI: 10.2320/jinstmet.71.258  

  108. Current-driven resistance oscillation in exchange-biased spin valves with a low aspect ratio 査読有り

    Y. Jiang, N. Tezuka, K. Inomata

    APPLIED PHYSICS LETTERS 89 (12) 122514-1-122514-3 2006年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2356376  

    ISSN:0003-6951

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    The authors report on current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valve nanopillars with a low aspect ratio of 1. Due to the complex domain structure of the nanopillars, an intermediate resistance state has been clearly observed in the CIMS curve. A distinctive current-driven resistance oscillation and a very low critical current density of 6x10(5) A/cm(2) have been demonstrated and explained to result from the competition between magnetic field, spin torque, and thermal activation. (c) 2006 American Institute of Physics.

  109. Tunnel magnetoresistance for junctions with epitaxial full-Heusler Co2FeAl0.5Si0.5 electrodes with B2 and L2(1) structures 査読有り

    N. Tezuka, N. Ikeda, A. Miyazaki, S. Sugimoto, M. Kikuchi, K. Inomata

    APPLIED PHYSICS LETTERS 89 (11) 112514-1-112514-3 2006年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2354026  

    ISSN:0003-6951

    eISSN:1077-3118

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    The tunnel magnetoresistance (TMR) effect has been investigated for magnetic tunnel junctions with epitaxial Co2FeAl0.5Si0.5 Heusler electrodes with B2 and L2(1) structures on a Cr-bufferd MgO substrate. The epitaxially grown Co2FeAl0.5Si0.5 has B2 structure when annealed below 400 degrees C, and has L2(1) structure for annealing above 450 degrees C. The TMR ratio of 76% at room temperature and 106% at 5 K were obtained for a MgO(001)/Cr/B2-type Co2FeAl0.5Si0.5/Al oxide/Co75Fe25/IrMn/Ta. The TMR ratio is larger than that of magnetic tunnel junction with an L2(1)-type electrode, which may be due to the smoother surface of the B2 structure and disordered L2(1) structure due to the Cr atom interdiffusion. (c) 2006 American Institute of Physics.

  110. Spin polarization of Co2FeSi full-Heusler alloy and tunneling magnetoresistance of its magnetic tunneling junctions 査読有り

    Z. Gercsi, A. Rajanikanth, Y. K. Takahashi, K. Hono, M. Kikuchi, N. Tezuka, K. Inomata

    APPLIED PHYSICS LETTERS 89 (8) 082512-1-082512-3 2006年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2338025  

    ISSN:0003-6951

    eISSN:1077-3118

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    The authors report spin polarization (P) and tunneling magnetoresistance (TMR) of epitaxially grown Co2FeSi thin films on a MgO (001) substrate. A Heusler-type L2(1) structure was observed in the samples sputter deposited at 473 K or above. The P value of the ordered film was measured as 0.49 +/- 0.02 by the point contact Andreev reflection (PCAR) technique. The TMR values obtained from the magnetic tunneling junction (MTJ) using the Co2FeSi electrode and Al-oxide barrier were 67.5% at 5 K and 43.6% at 298 K, respectively. The P value estimated from the TMR using Julliere's model matches the spin polarization measured by the PCAR very well, indicating that the TMR value from the MTJ is governed by the intrinsic value of P of the electrode material for incoherent tunneling.

  111. Indirect exchange spring between FePt and Fe with a Ru interlayer 査読有り

    J Jiang, N Tezuka, K Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 302 (1) 40-46 2006年7月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2005.08.009  

    ISSN:0304-8853

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    Indirect exchange spring in magnetron-sputtered FePt/Ru/Fe trilayers as well as multilayers have been investigated. Interlayer exchange Coupling between FePt and Fe layers through a Ru spacer was obtained with an oscillation period of about 1 nm. Magnetic properties of FePt thin films with different nominal thicknesses deposited on MgO (110) substrates at 400 degrees C showed that 12.5 rim thick FePt film had both high coercivity and good squareness. In FePt/Ru/Fe trilayers, ferromagnetic coupling between the two magnetic layers was achieved with a 0.5 nm thick Ru layer, and the saturated magnetization was largely improved after using interlayer exchange coupling with Fe while the coercivity changed little, which indicated that indirect exchange spring was a promising approach for high-performance magnets. Multilayers with such structures had also been studied with different thickness ratio of the two magnetic layers and strong exchange coupling was achieved as Fe thickness ratio increased. (c) 2005 Published by Elsevier B.V.

  112. Structural dependence of the tunnel magnetoresistance for magnetic tunnel junctions with a full-Heusler Co2Fe(Al,Si) electrode 査読有り

    N. Tezuka, S. Okamura, A. Miyazaki, M. Kikuchi, K. Inomata

    JOURNAL OF APPLIED PHYSICS 99 (8) 08T314 -1-08T314 -3 2006年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2167069  

    ISSN:0021-8979

    eISSN:1089-7550

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    We have investigated the crystal structure and magnetic moment of the Co2FeAl and Co2FeSi films deposited onto thermally oxidized Si and MgO(100) single-crystal substrates, and the structural effect on the tunnel magnetoresistance (TMR) of the magnetic tunnel junctions (MTJs) using a Co(2)FeZ (Z=Al or Si). The structure was changed by the substrate and postannealing temperatures, in which the fully epitaxial and polycrystalline Co2FeAl and Co2FeSi films were obtained with the different disorder structure. The magnetic moment of Co2FeAl films was found to be uninfluenced by the crystal structure. Spin-valve-type MTJs consisting of Co(2)FeZ(100 nm)/Al(1.2 nm)-oxide/Co75Fe25(2 nm)/IrMn(10 nm)/Ta(60 nm) were fabricated (Z=Al or Si) on thermally oxidized Si and MgO(100) single-crystal substrates. The maximum TMR obtained is about 50% at room temperature for MTJs with Co2FeAl films, regardless of the crystal structure of Co2FeAl. (C) 2006 American Institute of Physics.

  113. Structural and magnetic properties and tunnel magnetoresistance for Co-2(Cr,Fe)Al and Co2FeSi full-Heusler alloys 査読有り

    K Inomata, S Okamura, A Miyazaki, M Kikuchi, N Tezuka, M Wojcik, E Jedryka

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 39 (5) 816-823 2006年3月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/39/5/S07  

    ISSN:0022-3727

    eISSN:1361-6463

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    We have investigated the structure and magnetization of Co-2(Cr1-xFex)Al (0 &lt;= x &lt;= 1) and Co2FeSi full-Heusler alloy films deposited on thermally oxidized Si (SiO2) and MgO (001) single crystal substrates by ultra-high vacuum sputtering at various temperatures. The films were also post-annealed after deposition at room temperature (RT). Magnetic tunnel junctions with a full-Huesler alloy electrode were fabricated with a stacking, structure of Co-2 YZ (20 nm)/Al (1.2 nm)-oxide/Co75Fe25 (3 nm)/IrMn (15 nm)/Ta (60 nm) and microfabricated using electron beam lithography and Ar ion etching with a 10(2) mu m(2) junction area, where Co-2 YZ stands for Co-2(Cr1-xFex)Al or Co2FeSi. The tunnel barriers were formed by the deposition of 1.2 nrn Al, followed by plasma oxidization in the chamber. The x-ray diffraction revealed the A2 or B2 structure depending on heat treatment conditions and the substrate, but not L2(1) structure for the Co-2(Cr1-xFex)Al (0 &lt;= x &lt;= 1) films. The L2(1) structure, however, was obtained for the Co2FeSi films when deposited on a MgO (001) substrate at elevated temperatures above 473 K. The maximum tunnelling magnetoresistance (TMR) was obtained with 52% at RT and 83% at 5 K for a junction using a Co-2(Cr0.4Fe0.6)Al electrode. While the junction using a Co2FeSi electrode with the L2(1) structure exhibited the TMR of 41% at RT and 60% at 5 K. which may be improved by using a buffer layer for reducing the lattice misfit between the Co2FeSi and MgO (001) substrate.

  114. Quantum oscillation of the tunneling conductance in fully epitaxial double barrier magnetic tunnel junctions 査読有り

    T Nozaki, N Tezuka, K Inomata

    PHYSICAL REVIEW LETTERS 96 (2) 027208-1-027208-4 2006年1月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.96.027208  

    ISSN:0031-9007

    eISSN:1079-7114

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    We investigated spin-dependent tunneling conductance properties in fully epitaxial double MgO barrier magnetic tunnel junctions with layered nanoscale Fe islands as a middle layer. Clear oscillations of the tunneling conductance were observed as a function of the bias voltage. The oscillation, which depends on the middle layer thickness and the magnetization configuration, is interpreted by the modulation of tunneling conductance due to the spin-polarized quantum well states created in the middle Fe layer. This first observation of the quantum size effect in the fully epitaxial double barrier magnetic tunnel junction indicates great potential for the development of the spin-dependent resonant tunneling effect in coherent tunneling regime.

  115. ナノドットFe中間層を有するエピタキシャル強磁性2重トンネル接合におけるコンダクタンスの振動現象 査読有り

    野崎 隆行, 中村 新一, 手束 展規, 杉本 諭, 猪俣 浩一郎

    日本応用磁気学会誌 30 (2) 180-183 2006年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.30.180  

    ISSN:0285-0192

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    Double-barrier magnetic tunnel junctions (DMTJs) with an Fe(001) / MgO(001) / Fe(001) / MgO(001) / Fe(001) structure were deposited upon MgO(001) substrates by using molecular beam epitaxy. The DMTJs were found to show the TMR ratio of up to 110% and an extremely small bias voltage dependence (V<SUB>1/2</SUB> = 1.4 V under a positive bias application) at room temperature. We also investigated the middle-layer thickness dependence of the conductance curve in the DMTJs. Clear oscillations of the conductance were observed in a parallel magnetization configuration. This oscillation is thought to originate in the modulation of the tunneling conductance by the spin-polarized quantum well states created in the middle Fe layer.

  116. MgO基板上に作製したCo2V0.67Fe0.33Al薄膜の構造と磁性およびトンネル磁気抵抗 査読有り

    宮崎彩, 岡村進, 杉本諭, 手束展規, 猪俣浩一郎

    日本応用磁気学会誌 30 (3) 378-382 2006年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.30.378  

    ISSN:0285-0192

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    Co<sub>2</sub>V<sub>0.67</sub>Fe<sub>0.33</sub>Al full-Heulser alloy films were fabricated on an MgO (100) single crystalline substrate by using two different heat treatments: substrate heating and post-annealing. Ultra-high-vacuum dc magnetron sputtering was used to prepare the sample. The <i>L</i>2<sub>1</sub> structure was obtained when the substrate temperature (T<sub>s</sub>) was 500°C. For the same sample, the magnetic moment per formula unit showed the highest value of 2.4 μB at 5 K. There were small differences between the samples fabricated by substrate heating and post-annealing in terms of their structural and magnetic properties. A magnetic tunnel junction (MTJ) using Co<sub>2</sub>V<sub>0.67</sub>Fe<sub>0.33</sub>Al as a bottom electrode was fabricated. A larger tunnel magnetoresistance (TMR) was obtained by substrate heating than post-annealing with a maximum value of 28% at RT and 50% at 5 K when the Co<sub>2</sub>V<sub>0.67</sub>Fe<sub>0.33</sub>Al was sputtered at T<sub>s</sub> = 500°C. We found that there is an intimate relationship between the lattice constant of Co<sub>2</sub>V<sub>0.67</sub>Fe<sub>0.33</sub>Al and the TMR.

  117. 不規則構造を有するCo2(Cr1-xFex)Alを用いた強磁性トンネル接合のTMR特性 査読有り

    岡村進, 宮崎彩, 手束展規, 杉本諭, 猪俣浩一郎, 高橋有紀子, 宝野和博

    日本応用磁気学会誌 30 (3) 366-369 2006年

    出版者・発行元:公益社団法人 日本磁気学会

    DOI: 10.3379/jmsjmag.30.366  

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    Polycrystalline and single crystalline thin films of Co<sub>2</sub>(Cr<sub>1-<i>x</i></sub>Fe<sub><i>x</i></sub>)Al (<i>x</i> = 0.6, 1) full-Heusler alloys with different disordering were prepared on thermally oxidized Si and MgO(001) substrates, respectively, by the dc magnetron sputtering method. The magnetic tunnel junctions with a polycrystalline and single crystalline <i>B</i>2 type Co<sub>2</sub>FeAl (<i>x</i> =1) electrode demonstrate TMR of 70% and 75% at 5 K, respectively, which is larger than that of 65% at 5 K for Co<sub>75</sub>Fe<sub>25</sub>, indicating that the spin polarization for Co<sub>2</sub>FeAl is larger than that for Co<sub>75</sub>Fe<sub>25</sub>. The TMR for Co<sub>2</sub>FeAl with both the <i>A</i>2 and the <i>B</i>2, which is controlled by substrate heating, is almost the same, whereas for Co<sub>2</sub>(Cr<sub>0.4</sub>Fe<sub>0.6</sub>)Al the TMR increases with increasing the degree of ordering, corresponding to the first-principles calculations.

  118. 不規則構造を有するCo2(Cr1-xFex)Alフルホイスラー合金を用いた強磁性トンネル接合の磁気抵抗効果 査読有り

    岡村進, 宮崎彩, 手束展規, 杉本諭, 猪俣浩一郎, 高橋有紀子, 宝野和博

    電気学会論文誌A 126 276-280 2006年

    DOI: 10.1541/ieejfms.126.276  

  119. エアロゾル・デポジッション法により作製したFe/Ni-Zn-Cuフェライト複合膜における組成制御と電磁ノイズ抑制効果 査読有り

    チャンビサル, 杉本諭, 猪俣浩一郎, 手束展規, 明度純

    日本応用磁気学会誌 30 (5) 505-509 2006年

    出版者・発行元:None

    DOI: 10.3379/jmsjmag.30.505  

    ISSN:0285-0192

  120. L21構造を持つCo2CrGaフルホイスラー合金薄膜の作製とそれを用いた強磁性トンネル接合素子のトンネル磁気抵抗 査読有り

    正木達章, 菊地麻樹, 手束展規, 杉本諭, 猪俣浩一郎, 貝沼亮介, 石田清仁

    日本応用磁気学会誌 30 (4) 455-458 2006年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.30.455  

    ISSN:0285-0192

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    We have investigated that the structural and magnetic properties of Co<sub>2</sub>CrGa full-Heusler alloy films and researched the tunnel magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) using a Co<sub>2</sub>CrGa electrode on a MgO(100) substrate. Co<sub>2</sub>CrGa films were fabricated with substrate heating (RT ≤ <i>T</i><sub>s</sub> ≤ 500°C) or post-annealing (RT ≤ <i>T</i><sub>a</sub> ≤ 500°C) after the deposition using an ultrahigh vacuum dc magnetron sputtering system. L2<sub>1</sub>-ordered Co<sub>2</sub>CrGa thin films were obtained at <i>T</i><sub>s</sub> ≥ 300°C or <i>T</i><sub>a</sub> ≥ 200°C. The maximum magnetic moment per formula unit measured at 5 K were 2.8 μ<sub>B</sub> and 2.6 μ<sub>B</sub> for <i>T</i><sub>S</sub> and <i>T</i><sub>a</sub> = 400°C, respectively, which are over 85% of the theoretical value. The maximum TMR of 18% at RT and 42% at 5 K are obtained for the MTJ using the L2<sub>1</sub>-structured Co<sub>2</sub>CrGa film as a bottom electrode. It is expected that the TMR can be enhanced by optimizing the interface of Co<sub>2</sub>CrGa/AlOx.

  121. Magnetic properties of epitaxial Co2Cr1-xFexAl full Heusler alloy thin films with the L2(1) structure 査読有り

    A Hirohata, H Kurebayashi, S Okamura, N Tezuka, K Inomata

    IEEE TRANSACTIONS ON MAGNETICS 41 (10) 2802-2804 2005年10月

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

    DOI: 10.1109/TMAG.2005.854831  

    ISSN:0018-9464

    eISSN:1941-0069

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    Co2Cr1-xFexAl full Hensler alloy thin films (x &gt; 0.4) have been epitaxially grown on GaAs(001) substrates under the optimized condition. Structural analysis reveals the detailed growth mechanism of the films and confirms that the films form the perfectly ordered L2(1) structure. A magnetization measurement also shows the films possess very strong uniaxial crystalline anisotropy due to the epitaxial growth. By using these films as bottom electrodes of magnetic tunnel junctions, the maximum tunnel magnetoresistance ratio of 8.8% is observed after post-annealing with Al-O insulating barriers for x = 1.

  122. Magnetic transport mechanism in double ferromagnetic tunnel junctions with two-dimensional ferromagnetic particles 査読有り

    H Sukegawa, A Hirohata, S Nakamura, N Tezuka, S Sugimoto, K Inomata

    IEEE TRANSACTIONS ON MAGNETICS 41 (10) 2679-2681 2005年10月

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

    DOI: 10.1109/TMAG.2005.855292  

    ISSN:0018-9464

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    Magnetic transport properties of Co90Fe10/AIO(infinity) /Co90Fe10/AIO(x)/Co90Fe10 ferromagnetic-double tunnel junctions have been investigated with respect to the thermal fluctuation. A middle Co90Fe10 layer is discontinuous by forming Co90Fe10 particles two-dimensionally, which shows superparAmagnetic behavior above 80 K. The average diameter of the Co90Fe10 particles is estimated to be 4.8-5.0 nm from both a magnetization curve at room temperature and temperature dependence of coercivities deduced from magnetoresistance curves. This finding agrees with the maximum diameter (5.2 nm) evaluated from cross-sectional transmission electron microscope images, revealing that the dominant electron transport process heavily depends on the largest particles.

  123. Exchange coupling between FePt and Fe through Ru interlayer 査読有り

    JH Jiang, N Tezuka, K Inomata

    JOURNAL OF APPLIED PHYSICS 98 (6) 063902-1-063902-3 2005年9月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2058189  

    ISSN:0021-8979

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    Interlayer exchange coupling in magnetron-sputtered FePt/Ru/Fe trilayers has been investigated. The thickness dependence of in-plane magnetic properties of FePt thin films was investigated and a 12.5-nm-thick FePt film showed both high coercivity and good squareness. The exchange coupling between FePt and Fe layers through a Ru interlayer was obtained with an oscillatory period of about 1 nm. A 0.5 nm Ru layer produced a ferromagnetic coupling between the two magnetic layers and the saturated magnetization is considerably improved through interlayer exchange coupling with Fe. (c) 2005 American Institute of Physics.

  124. Large tunnel magnetoresistance at room temperature with a Co2FeAl full-Heusler alloy electrode 査読有り

    S Okamura, A Miyazaki, S Sugimoto, N Tezuka, K Inomata

    APPLIED PHYSICS LETTERS 86 (23) 232503-1-232503-3 2005年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1944893  

    ISSN:0003-6951

    eISSN:1077-3118

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    Magnetic tunnel junctions (MTJs) with a Co2FeAl Heusler alloy electrode are fabricated by the deposition of the film using an ultrahigh vacuum sputtering system followed by photolithography and Ar ion etching. A tunnel magnetoresistance (TMR) of 47% at room temperature (RT) are obtained in a stack Of Co2FeAl/Al-O-x/Co75Fe25 magnetic tunnel junction (MTJ) fabricated on a thermally oxidized Si substrate despite the A2 type atomic site disorder for Co2FeAl. There is no increase of TMR in MTJs with the B2 type Co2FeAl, which is prepared by the deposition on a heated substrate. X-ray photoelectron spectroscopy (XPS) depth profiles in Co2FeAl single layer films reveal that Al atoms in Co2FeAl are oxidized preferentially at the surfaces. On the other hand, at the interfaces in Co2FeAl/Al-O-x/CO75Fe25 MTJs, the ferromagnetic layers are hardly oxidized during plasma oxidation for a formation of A] oxide barriers. (c) 2005 American Institute of Physics.

  125. Distinctive current-induced magnetization switching in a current-perpendicular-to-plane giant-magnetoresistance nanopillar with a synthetic antiferromagnet free layer 査読有り

    T Ochiai, Y Jiang, A Hirohata, N Tezuka, S Sugimoto, K Inomata

    APPLIED PHYSICS LETTERS 86 (24) 242506-1-242506-3 2005年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1949709  

    ISSN:0003-6951

    eISSN:1077-3118

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    We investigated current-induced magnetization switching (CIMS) in two types of pseudo-spin-valve nanopillars with current-perpendicular-to-plane giant magnetoresistance (CPP-GMR); Co90Fe10 s(10) nmd/Cu(10 nm)/Co90Fe10(2.5 nm) sconventional typed and Co(90)Fe(10)s(10) nmd/ Cus10 nmd/ Co90Fe1(1.5 nmd/ Rus0.45 nmd/ Co90Fe10(2.5 nmd (synthetic antiferromagnet; SyAF typed. We observed the CIMS in the both CPP-GMR structures at room temperature. In particular for the SyAF type nanopillars, the CIMS was observed only in a negative current regime. We also discovered that the applied magnetic field dependence of the CIMS shows absolutely different behavior from that of the conventional type. These peculiar CIMS behaviors with the SyAF free layer are attributed to majority electron spin transfer torque from the thick to the thin Co90Fe10 layers, enhanced by the presence of a Ru layer. (c) 2005 American Institute of Physics.

  126. Structural and magnetic properties of epitaxial L2(1)-structured Co-2(CrFe)Al films grown on GaAs(001) substrates 査読有り

    A Hirohata, H Kurebayashi, S Okamura, M Kikuchi, T Masaki, T Nozaki, N Tezuka, K Inomata

    JOURNAL OF APPLIED PHYSICS 97 (10) 103714-1-103714-8 2005年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1888050  

    ISSN:0021-8979

    eISSN:1089-7550

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    We have successfully grown both L2(1) polycrystalline Co(2)CrA1 and epitaxial L2(1)-structured Co(2)FeA1 films onto GaAs(001) substrates under an optimized condition. Both structural and magnetic analyses reveal the detailed growth mechanism of the alloys, and suggest that the CO(2)CrA1 film contains atomically disordered phases, which decreases the magnetic moment per f.u., while the Co(2)FeA1 film satisfies the generalized Slater-Pauling behavior. By using these films, magnetic tunnel junctions (MTJs) have been fabricated, showing 2% tunnel magnetoresistance (TMR) for the Co(2)CrA1 MTJ at 5 K and 9% for the CO2FeAl MTJ at room temperature (RT). Even though the TMR ratio still needs to be improved for future device applications, these results explicitly include that the CO2(Cr,Fe)A1 full Heusler alloy is a promising compound to achieve half-metallicity at RT by controlling both disorder and surface structures in the atomic level by manipulating the Fe concentration. (c) 2005 American Institute of Physics.

  127. Spin transfer in antisymmetric exchange-biased spin-valves 査読有り

    Y Jiang, GH Yu, YB Wang, J Teng, T Ochiai, N Tezuka, K Inomata

    APPLIED PHYSICS LETTERS 86 (19) 192515-1-192515-3 2005年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1927694  

    ISSN:0003-6951

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    In this letter, we report on measurements of current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valves (ESPVs). The structures of the ESPVs are all "antisymmetric" but with different thickness of a ruthenium (Ru) layer. It is confirmed that the "antisymmetric" structures largely enhance the spin transfer effect and therefore reduce critical current densities for the CIMS. The effect of the Ru layer on the spin transfer in the ESPVs is also systematically studied. With a decrease of the Ru layer&apos;s thickness, the critical current densities can be further reduced. The lowest critical current we achieved in an "antisymmetric" structure is 1 x 10(6) A/cm(2), which realizes a reduction of more than one order of magnitude compared with all the reported works. (c) 2005 American Institute of Physics.

  128. CPP-GMR enhancement in spin valves using a thin Ru layer 査読有り

    N Tezuka, S Abe, Y Jiang, K Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 290 1150-1153 2005年4月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2004.11.499  

    ISSN:0304-8853

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    Current perpendicular to plane giant magnetoresistance (CPP-GMR) of single spin valves with two kinds free layers has been investigated. One is a single ferromagnetic layer (Conventional structure) and the other is a ferromagnetic layer with thin Ru cap layer (Ru cap structure). Both structure had increasing resistance and resistance changes with decreasing element size. The CPP-GMR ratio for a Ru cap structure was enhanced from 0.70 to 4.3% at room temperature. We think the MR enhancement is caused by the spin dependent scattering due to strong reflection of majority spins at the Co90Fe10/Ru interface. &COPY; 2004 Elsevier B.V. All rights reserved.

  129. Significant magnetoresistance enhancement due to a cotunneling process in a double tunnel junction with single discontinuous ferromagnetic layer insertion 査読有り

    H Sukegawa, S Nakamura, A Hirohata, N Tezuka, K Inomata

    PHYSICAL REVIEW LETTERS 94 (6) 068304-1-068304-4 2005年2月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.94.068304  

    ISSN:0031-9007

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    We fabricate CoFe/AlOx/CoFe/AlOx/CoFe ferromagnetic double tunnel junctions and observe spindependent tunneling phenomena. A middle CoFe layer becomes discontinuous by forming CoFe particles two dimensionally, of which the average diameter is evaluated to be 2.0-4.5 nm from cross-sectional transmission electron microscopy images. Below 50 K, a Coulomb gap is observed in current-voltage curves, and both magnetoresistance ratios and resistances are found to increase significantly with decreasing temperature. This indicates that a cotunneling process is dominant within the gap, which agrees very well with theoretical prediction [Phys. Rev. Lett. 80, 1758 (1998)].

  130. Bias voltage effect on tunnel magnetoresistance in fully epitaxial MgO double-barrier magnetic tunnel junctions 査読有り

    T Nozaki, A Hirohata, N Tezuka, S Sugimoto, K Inomata

    APPLIED PHYSICS LETTERS 86 (8) 082501-1-082501-3 2005年2月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1867559  

    ISSN:0003-6951

    eISSN:1077-3118

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    Double-barrier magnetic tunnel junctions (DMTJs), consisting of a fully epitaxial Fe(001)/MgO(001)/Fe(001)/MgO(001)/Fe(001) structure, have been deposited onto MgO (001) single-crystal substrates using molecular-beam epitaxy, and have been characterized by measuring the bias voltage effects on both tunneling magnetoresistance (TMR) and conductance. The DMTJs are found to show large TMR ratios of up to 110% and extremely small bias voltage dependence (V-half= 1.44 V under a positive bias application) compared with conventional magnetic tunnel junctions (MTJs) with a single MgO barrier at room temperature. In addition, clear asymmetry is observed in the bias voltage dependence of the TMR ratios with respect to the signs of the bias, which corresponds to the asymmetric bias dependence of the conductance, especially for a parallel magnetization configuration. Such a high V-half with a large TMR ratio is relevant for a high-output MTJ cell for future spintronic devices. (c) 2005 American Institute of Physics.

  131. Magnetic properties of L21-structured Co2(Cr,Fe)Al films grown on GaAs(001) substrates 査読有り

    A. Hirohata, H. Kurebayashi, S. Okamura, T. Masaki, T. Nozaki, M. Kikuchi, N. Tezuka, K. Inomata, J.S. Claydon, Y.B. Xu

    JOURNAL OF APPLIED PHYSICS 97 10C308-1-10C308-3 2005年

    DOI: 10.1063/1.1854256  

  132. L21構造を有するCo2Cr1-xFexAl薄膜の結晶構造と磁気特性 査読有り

    廣畑 貴文, 紅林 秀和, 岡村 進, 菊地 麻樹, 正木 達章, 野崎 隆行, 手束 展規, 猪俣 浩一郎

    日本応用磁気学会誌 29 (2) 124-127 2005年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.29.124  

    ISSN:0285-0192

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    We successfully grew Co<sub>2</sub>Cr<sub>1-<i>x</i></sub>Fe<sub><i>x</i></sub>Al full Heusler films (0 ≤ <i>x</i> ≤ 1) with the L2<sub>1</sub> structure onto GaAs(001) substrates by achieving stoichiometry in an ultrahigh-vacuum molecular beam epitaxy chamber. The films develop epitaxial crystallinity with the relationship of Co<sub>2</sub>Cr<sub>1-<i>x</i></sub>Fe<sub><i>x</i></sub>Al(001)‹110›||GaAs(001)‹110›, which induces very strong uniaxial magnetocrystalline anisotropy, except for <i>x</i> = 0. For <i>x</i> = 1, in particular, the film is almost a single phase and its magnetic moment per formula unit exhibits Slater-Pauling behavior. Films of this type were used to fabricate magnetic tunnel junctions with 8.8% and 4.9% tunnel magnetoresistance (TMR) ratios at room temperature for <i>x</i> = 1 with an Al-O tunnel barrier and <i>x</i> = 0.6 with a MgO barrier, respectively. The TMR ratio can be further enhanced by both realizing an L2<sub>1</sub> single phase and eliminating lattice distortion.

  133. 強磁性ナノドット層を有する二重トンネル接合におけるTMRの増大 査読有り

    介川 裕章, 中村 新一, 廣畑 貴文, 手束 展規, 猪俣 浩一郎, 杉本 諭

    日本応用磁気学会誌 29 (3) 274-277 2005年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.29.274  

    ISSN:0285-0192

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    We observed spin-dependent tunneling in Co<sub>90</sub>Fe<sub>10</sub>/AlO<sub><i>x</i></sub>/Co<sub>90</sub>Fe<sub>10</sub>/AlO<sub><i>x</i></sub>/Co<sub>90</sub>Fe<sub>10</sub> ferromagnetic double tunnel junctions. A middle Co<sub>90</sub>Fe<sub>10</sub> layer, which is inserted between two AlO<sub><i>x</i></sub> layers, is discontinuous due to the difference in the surface energy of these layers. The average diameter of Co<sub>90</sub>Fe<sub>10</sub> particles was estimated to be 2.0-4.5 nm from cross-sectional transmission electron microscopy (TEM) images. At low temperature (< 50 K), a Coulomb gap is observed in current-voltage (<i>I-V</i>) curves, and the tunnel magnetoresistance (TMR) ratio within the gap enhances significantly with decreasing temperature, which indicates that the dominant electron transport is inelastic co-tunneling within the Coulomb gap. These observations in a ferromagnetic tunnel junction with 2-dimensional magnetic nano-particle layer insertion accord well with theoretical predictions by Takahashi and Maekawa [Phys. Rev. Lett. 80, 1758 (1998)].

  134. Co2CrGaフルホイスラー合金薄膜の結晶構造と磁気・電気伝導特性 査読有り

    菊地 麻樹, 正木 達章, 手束 展規, 杉本 諭, 猪俣 浩一郎

    日本応用磁気学会誌 29 (4) 455-458 2005年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.29.455  

    ISSN:0285-0192

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    We investigated the structural, magnetic and electrical transport properties of Co<sub>2</sub>CrGa full Heusler alloy films, and optimized the growth conditions, achieving stoichiometric films. The crystalline structures and the magnetic and electrical transport properties were found to depend on the film thickness, <i>t</i><sub>CCG</sub>. An ordered <i>L</i>2<sub>1</sub> structure was obtained for <i>t</i><sub>CCG</sub>≥100 nm. The saturation magnetization decreases with decreasing film thickness and vanishes below <i>t</i><sub>CCG</sub>=23 nm, indicating the existence of a magnetically dead layer in the vicinity of the substrates. For <i>t</i><sub>CCG</sub>=150 nm, the saturation magnetization is 602 emu/cm<sup>3</sup> (3.1 μ<sub>B</sub>) at 5 K, which agrees very well with the theoretical value. The resistivity of the samples with <i>t</i><sub>CCG</sub>≤150 nm decreases with increasing temperature, while that with <i>t</i><sub>CCG</sub>=300 nm increases. By using films with <i>t</i><sub>CCG</sub>=100 nm and 300 nm as bottom electrodes, forming an <i>L</i>2<sub>1</sub> structure, magnetic tunnel junctions (MTJs) were also fabricated, showing 5.0% and 1.4% tunnel magnetoresistance (TMR) at RT, respectively.

  135. Structural, magnetic, and transport properties of full-Heusler alloy Co-2(Cr1-xFex)Al thin films 査読有り

    S Okamura, R Goto, S Sugimoto, N Tezuka, K Inomata

    JOURNAL OF APPLIED PHYSICS 96 (11) 6561-6564 2004年12月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1810207  

    ISSN:0021-8979

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    The structural, magnetic, and transport properties are investigated for full-Heusler alloy Co-2(Cr1-xFex)Al (CCFA) thin films sputtered on thermally oxidized Si substrates at room temperature (RT). X-ray diffraction reveals that the films possess the B2 structure for x=0, decrease the atomic site ordering by substituting Fe for Cr (0.4less than or equal toxless than or equal to0.6), and form the A2 structure for x=1. Both the magnetic moment and the Curie temperature of the films increase with increasing Fe content (x), although the moment for x&lt;1 is significantly smaller than that of the calculated value for the L2(1) structure. Magnetic tunnel junctions (MTJs) with CCFA films as either upper or bottom ferromagnetic layers are also fabricated by using metal masks. The maximum tunneling magnetoresistance (TMR) at RT for the MTJ was observed to be 19.1% for x=0.4 with the CCFA film as an upper ferromagnetic layer, despite the atomic disorder of the CCFA film. This is consistent with our previous TMR observation with the CCFA film as a bottom ferromagnetic layer, indicating that the CCFA film even with the B2 structure is a good candidate for future spintronic devices due to its disorder tolerance, high reproducibility, and large spin polarization. (C) 2004 American Institute of Physics.

  136. Tunnel magneto resistance using full-Heusler alloys 査読有り

    K Inomata, S Okamura, N Tezuka

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 282 269-274 2004年11月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2004.04.063  

    ISSN:0304-8853

    eISSN:1873-4766

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    We grew Co-2(Cr1-xFex)Al Heusler alloy films at room temperature (RT) without any buffer layers as well as Co(2)MnZ (Z = Si and Ge), which were fabricated using a Cr buffer at RT and elevated temperatures, on thermally oxidized Si substrates using a magnetron sputtering system. The X-ray diffraction pattern of the Co(2)MnZ (Z = Si and Ge) films exhibited L2(1) structure when deposited at an elevated temperature, while it showed amorphous or nanocrystalline nature for the films deposited at RT. Co-2(Cr1-xFex)Al films deposited at RT, on the other hand, revealed the B2 and A2 structures, depending on the Fe concentration x, in which the structure tends to become the A2 with increasing x, which is different from the L21 structure as expected in the bulk. The magnetic moment and the Curie temperature monotonically increased with increasing x. Spin-valve-type tunneling junctions consisting of Co2Cr1-x, FexAl (100 nm)/AlOx (1.4 nm)/CoFe (3 nm)/NiFe (5 nm)/IrMn (15 nm)/Ta (10 nm) were fabricated at RT on thermally oxidized Si substrates without any buffer layers using metal masks. The maximum tunneling magneto resistance obtained is 19% for x = 0.4 at room temperature. (C) 2004 Elsevier B.V. All rights reserved.

  137. Spin-dependent quantum oscillations in magnetic tunnel junctions with Ru quantum wells 査読有り

    T Nozaki, Y Jiang, Y Kaneko, A Hirohata, N Tezuka, S Sugimoto, K Inomata

    PHYSICAL REVIEW B 70 (17) 172401-172401 2004年11月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevB.70.172401  

    ISSN:1098-0121

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    The influence of quantum-well (QW) states formed in a Ru spacer layer on tunneling magnetoresistance (TMR) was investigated. A magnetic tunnel junction (MTJ) with a Ru spacer inserted between an AlOx tunnel barrier and one of the ferromagnetic Co90Fe10 layers was deposited on a single crystal MgO(110) substrate using an ultrahigh vacuum sputtering system. We clearly observe an oscillation of TMR ratios as a function of Ru thickness up to 1.7 nm with the same phase previously observed in an interlayer exchange coupling. The TMR ratios also oscillate and change their signs under both positive and negative bias voltage applications for the Ru thickness more than 1.3 nm. These periodical oscillations are caused by the oscillation of spin polarization derived from the contribution of QW states of up spin electrons confined in the Ru spacer layer to the spin-dependent electron transport.

  138. Effect of the soft/hard exchange interaction on natural resonance frequency and electromagnetic wave absorption of the rare earth-iron-boron compounds 査読有り

    T Maeda, S Sugimoto, T Kagotani, N Tezuka, K Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 281 (2-3) 195-205 2004年10月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2004.04.105  

    ISSN:0304-8853

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    The effect of exchange interaction between the hard-magnetic Y2Fe14B and soft-magnetic Fe3B phases on the natural resonance phenomenon and microwave absorption properties was investigated. The Y2Fe14B/Fe3B ribbons were prepared by melt-spinning. The annealing at just above crystallization temperature of the ribbons and the Cu addition were effective to improve the exchange interaction between Y2Fe14B and Fe3B phases. A linear relationship between the recoil ratio and the shift of resonance frequency was confirmed. The Y9.4Fe79.3B11.1Cu0.2 ribbon, annealed at 1003 K, exhibited the largest recoil ratio of 0.49 and its resin composite showed the natural resonance frequency (f(r)) at 44 GHz, which was 23 GHz lower than that of the Y2Fe14B resin composite. The Y9.4Fe79.3B11.1Cu0.2 composite also exhibited good microwave absorption properties (over 99%) at 39.5 GHz with the absorber thickness of 0.38 mm. (C) 2004 Published by Elsevier B.V.

  139. Influence of synthetic antiferromagnet free layer on current-perpendicular-to-plane spin-valves 査読有り

    Y Jiang, S Abe, T Nozaki, N Tezuka, K Inomata

    IEEE TRANSACTIONS ON MAGNETICS 40 (4) 2245-2247 2004年7月

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

    DOI: 10.1109/TMAG.2004.830231  

    ISSN:0018-9464

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    We study current-perpendicular-to-plane (CPP) geometrical giant magnetoresistance (GMR) and magnetic switching property for single spin-valves (SVs). Applying a synthetic antiferromagnet (SyAF) instead of a single ferromagnet film as a free layer, the resistance-change area product DeltaRA of the SVs is strongly enhanced from similar to1.84 mOmega mum(2) to similar to16.8 mOmega mum(2) and the CPP-GMR ratio changes from 0.8% to 3.6%. The study of the magnetic switching behavior by both experiment and single-domain thermal activation modeling shows that the SVs with SyAF as a free layer approaches a single-domain magnet even with a low aspect ratio I as long as its size diminishes to similar to0.18 mum(2). Because of the single-domain structure, the SVs with SyAF give a size-independent magnetic switching field when the aspect ratio is 1.

  140. Magnetoresistance in tunnel junctions using Co-2(Cr,Fe)Al full Heusler alloys 査読有り

    K Inomata, N Tezuka, S Okamura, H Kurebayashi, A Hirohata

    JOURNAL OF APPLIED PHYSICS 95 (11) 7234-7236 2004年6月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1651813  

    ISSN:0021-8979

    eISSN:1089-7550

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    We grew Co-2(Cr1-xFex)Al Heusler alloy films using a magnetron sputtering system on thermally oxidized Si substrates at room temperature without any buffer layers. The x-ray diffraction patterns did not show the L2(1) structure as expected for the bulk but revealed the B2 and A2 structures, depending on the Fe concentration x, in which the structure tends to become the A2 with increasing x. The magnetic moment and the Curie temperature monotonically increased with increasing x. Spin-valve-type tunneling junctions consisting of Co2Cr1-xFexAl (100 nm)/AlOx (1.4 nm)/CoFe (3 nm)/NiFe (5 nm)/IrMn (15 nm)/Ta (10 nm) were fabricated on thermally oxidized Si substrates without any buffer layers using metal masks. The maximum tunneling magnetoresistance at room temperature was obtained as 19% for x=0.4. (C) 2004 American Institute of Physics.

  141. Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve 査読有り

    Y Jiang, T Nozaki, S Abe, T Ochiai, A Hirohata, N Tezuka, K Inomata

    NATURE MATERIALS 3 (6) 361-364 2004年6月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat1120  

    ISSN:1476-1122

    eISSN:1476-4660

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    Great interest(1-10) in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions(11,12) of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices(13): in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 108 to 107 A cm(-2). In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 x 10(6) A cm(-2). We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.

  142. Magnetic domain structures and switching properties in submicron size synthetic antiferromagnets 査読有り

    N. Tezuka, N. Koike, K. Sakurada, K. Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E1289-E1291 2004年5月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.jmmm.2003.12.403  

    ISSN:0304-8853

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    Magnetic domain structures and spin switching properties in submicron size synthetic antiferromagnets (SyAFs), Co90Fe10/Ru/Co90Fe10 with aspect ratio (k) of 1, have been studied by using magnetic force microscope (MFM) image under an external magnetic field and by a focused magneto-optic Kerr effect system. It is found that SyAF with k = 1 shows the single domain structure during magnetization reversal, and exhibits size- and shape-independent spin switching field. (C) 2003 Elsevier B.V. All rights reserved.

  143. Magnetic switching properties of magnetic tunnel junctions using a synthetic ferrimagnet free layer 査読有り

    T Nozaki, Y Jiang, H Sukegawa, N Tezuka, A Hirohata, K Inomata, S Sugimoto

    JOURNAL OF APPLIED PHYSICS 95 (7) 3745-3748 2004年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1669053  

    ISSN:0021-8979

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    Magnetic tunnel junctions (MTJs) using a synthetic ferrimagnet (SyF) free layer consisting of Co90Fe10/Ru/Co90Fe10 were deposited on a thermally oxidized Si substrate using an ultrahigh-vacuum sputtering system, and were patterned into micron to submicron sizes using electron-beam lithography and Ar ion milling. Magnetic switching properties and tunneling magnetoresistance (TMR) were investigated. A SyF free layer can maintain high remanence even for the aspect ratio of 1, and exhibits a size-independent switching field in all element widths from 0.25 to 16 mum investigated. Additionally, these MTJs show large TMR ratio up to 40% after annealing at 250 degreesC for 60 min. These results demonstrate that a SyF free layer can be applied to future spintronics nanodevices. (C) 2004 American Institute of Physics.

  144. Effective reduction of critical current for current-induced magnetization switching by a Ru layer insertion in an exchange-biased spin valve 査読有り

    Y Jiang, S Abe, T Ochiai, T Nozaki, A Hirohata, N Tezuka, K Inomata

    PHYSICAL REVIEW LETTERS 92 (16) 167204-1-167204-4 2004年4月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.92.167204  

    ISSN:0031-9007

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    Recently, it has been predicted that a spin-polarized electrical current perpendicular to plane directly flowing through a magnetic element can induce magnetization switching through spin-momentum transfer. In this Letter, the first observation of current-induced magnetization switching (CIMS) in exchange-biased spin valves (ESPVs) at room temperature is reported. The ESPVs show the CIMS behavior under a sweeping dc current with a very high critical current density. It is demonstrated that a thin ruthenium (Ru) layer inserted between a free layer and a top electrode effectively reduces the critical current densities for the CIMS. An "inverse" CIMS behavior is also observed when the thickness of the free layer increases.

  145. Co2Cr1-xFexAlフルホイスラー合金の構造と磁気・伝導特性 査読有り

    岡村進, 後藤龍太, 手束展規, 杉本諭, 猪俣浩一郎

    日本金属学会誌 68 114-117 2004年

    DOI: 10.2320/jinstmet.68.114  

  146. Zn0.4Fe2.6O4薄膜を用いた強磁性トンネル接合の磁気抵抗効果 査読有り

    西村和正, 手束展規, 杉本諭, 猪俣浩一郎

    日本金属学会誌 68 81-85 2004年

    DOI: 10.2320/jinstmet.68.82  

  147. スピン二重トンネル接合の磁気抵抗効果 査読有り

    介川裕章, 手束展規, 猪俣浩一郎, 杉本諭

    日本金属学会誌 68 74-77 2004年

    DOI: 10.2320/jinstmet.68.74  

  148. Co2(Cr1-xFex)Alフルホイスラー合金を用いたMTJの磁気抵抗効果 査読有り

    岡村 進, 後藤龍太, 手束展規, 杉本 諭, 猪俣浩一郎

    日本応用磁気学会誌 28 (2) 172-175 2004年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.28.172  

    ISSN:0285-0192

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    Co<sub>2</sub>CrAl (<i>x</i> = 0) films were found to form a B2 structure, and when Fe was substituted for Cr (<i>x</i> = 0.4−0.6), the films crystallized B2+A2 structures, while an A2 structure was stable in the case of Co<sub>2</sub>FeAl (<i>x</i> = 1) films deposited on thermally oxidized Si substrates at room temperature. The magnetic moments of the films containing Fe tended to increase with increasing <i>x</i>, while those of the films containing Cr were far from the values calculated with an assumption of the L2<sub>1</sub> structure ordering.<BR>Spin-valve-type tunneling junctions with a Co<sub>2</sub>(Cr<sub>1-<i>x</i></sub>Fe<sub><i>x</i></sub>) Al film were also fabricated, which demonstrated large tunneling magnetoresistance of 19.1% (<i>x</i>= 0.4) at room temperature and 27.2% at 5 K in spite of atomic site disorder.

  149. 極薄Ruキャップ層を用いたスピンバルブ素子のCPP-GMR特性 査読有り

    阿部 慎也, 山口 正彦, 手束 展規, 猪俣 浩一郎

    日本応用磁気学会誌 28 (9) 987-990 2004年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.28.987  

    ISSN:0285-0192

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    We have studied the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of single spin-valve (SV) films with two different free layers : one is a single ferromagnet layer (conventional), and the other is a ferromagnetic layer with a ruthenium cap layer (Ru cap). When the spacer Cu layer thickness is 2.5 nm and the Ru layer is 0.45 nm, the Ru cap-type greatly enhances the CPP-GMR, with increasing its value up to 4.3%. We argue that the MR enhancement is probably caused by the spin-dependent scattering due to the strong reflection of majority spins at the Co<sub>90</sub>Fe<sub>10</sub>/Ru interface.

  150. Enhanced Current-perpendicular-to-plane Giant Magnetoresistance in Single Spin-valve with Synthetic Antiferromagnet Free Layers 査読有り

    Y. Jiang, S. Abe, T. Nozaki, N. Tezuka, K. Inomata

    Transactions of the Materials Research Society of Japan 29 1531-1533 2004年

  151. Perpendicular giant magnetoresistance and magnetic switching properties of a single spin valve with a synthetic antiferromagnet as a free layer 査読有り

    Y Jiang, S Abe, T Nozaki, N Tezuka, K Inomata

    PHYSICAL REVIEW B 68 (22) 224426-1-224426-7 2003年12月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevB.68.224426  

    ISSN:1098-0121

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    We study the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) and magnetic switching behavior of single spin-valve (SV) films with two different free layers-one is a single ferromagnet (FM) layer, while the other is a synthetic antiferromagnet (SyAF) consisting of Co90Fe10/Ru/Co90Fe10. When the interlayer Cu thickness is 2.5 nm, the SyAF as a free layer greatly enhances the CPP-GMR of SVs from 0.8% to 3.6%. The GMR enhancement effect decreases with increasing interlayer Cu thickness. We argue that the MR enhancement by the SyAF is probably because of strong reflection of the majority spins by the interface between Co90Fe10 and ruthenium. Experimental and theoretical studies of the magnetic switching behavior show that the SVs with SyAF have a much better tendency to form a single magnetic domain than the conventional ones. The single domain structure results in a size-independent magnetic switching field of the SVs with SyAF at the low aspect ratio 1.

  152. Enhancement of current-perpendicular-to-plane giant magnetoresistance by synthetic antiferromagnet free layers in single spin-valve films 査読有り

    Y Jiang, S Abe, T Nozaki, N Tezuka, K Inomata

    APPLIED PHYSICS LETTERS 83 (14) 2874-2876 2003年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1616974  

    ISSN:0003-6951

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    Current-perpendicular-to-plane (CPP) geometrical giant magnetoresistance (GMR) single spin-valve (SPV) structures with synthetic antiferromagnets (SyAFs) as free layers were fabricated. The sample sizes range from micron to submicron. We demonstrate that SyAFs as free layers dramatically enhances the CPP-GMR ratio from 0.83% to 3.56% at room temperature and also double the resistance-area product in single SPV films. A study of the magnetic switching behavior by both experiment and single-domain thermal activation modeling shows that the CPP-GMR SPV with SyAF structure approaches that of a single-domain magnet even with low aspect ratio of 1 as long as its size diminishes to similar to0.18 mum(2). The single-domain structure brings size-independent magnetic switching field when the aspect ratio is 1. The large GMR ratio at room temperature, single-domain structure and size-independent magnetic switching field demonstrate the great potential of CPP-GMR SPVs with SyAF free layers for use in future ultrahigh density magnetic storage devices. (C) 2003 American Institute of Physics.

  153. Improved thermal stability of ferromagnetic tunnel junctions with a CoFe/CoFeOX/CoFe pinned layer 査読有り

    T Ochiai, N Tezuka, K Inomata, S Sugimoto, Y Saito

    IEEE TRANSACTIONS ON MAGNETICS 39 (5) 2797-2799 2003年9月

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

    DOI: 10.1109/TMAG.2003.815715  

    ISSN:0018-9464

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    Annealing temperature dependence of the tunnel magnetoresistance (TMR) ratio for magnetic tunnel junctions with CoFeOx inserted in the pinned layer was investigated. A junction with a CoFe/CoFeOx/CoFe pinned layer exhibited TMR ratios of 46.5% and 42.5% after annealing at 350 degreesC and 375 degreesC, respectively. The reason for the improvement of the thermal stability is related to oxygen diffusion from the CoFeOx layer, and there is a possibility that CoFeOx plays the role of a Mn (in MnIr exchange layer) diffusion barrier.

  154. Magnetization reversal and domain structure of antiferromagnetically coupled submicron elements 査読有り

    N Tezuka, N Koike, K Inomata, S Sugimoto

    JOURNAL OF APPLIED PHYSICS 93 (10) 7441-7443 2003年5月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1539074  

    ISSN:0021-8979

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    Switching characteristics and magnetic domain structures in submicron size synthetic antiferromagnets (SyAF), Co90Fe10/Ru/Co90Fe10 have been studied. Submicron size elements with well defined geometry were prepared by electron beam lithography and argon ion milling for SyAFs and Co90Fe10 monolayers deposited by an ultrahigh vacuum sputtering system. Hysteresis loops were obtained by a focused magneto-optic Kerr effect (MOKE) system and magnetic images in the remanent state were observed by magnetic force microscopy (MFM). We found that the MFM images of SyAF exhibit a single domain structure even in the case of aspect ratio of 1, and there is an optimum ferromagnetic film thickness at which SyAF can obtain a single domain structure with such a low aspect ratio. The MOKE results show that the switching field is dependent on the element width and aspect ratio. (C) 2003 American Institute of Physics.

  155. Size-independent spin switching field using synthetic antiferromagnets 査読有り

    K Inomata, N Koike, T Nozaki, S Abe, N Tezuka

    APPLIED PHYSICS LETTERS 82 (16) 2667-2669 2003年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1568823  

    ISSN:0003-6951

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    The arrays of the synthetic antiferromagnetic (SyAF) patterned bits consisting of Co90Fe10 (t(1)nm)/Ru (d nm)/Co90Fe10 (t(2) nm) were successfully fabricated with micron to submicron sizes and different aspect ratios. Magnetization switching field H-sw and magnetic domain structure were investigated using magneto-optical Kerr effect and magnetic force microscopy (MFM), respectively. It was demonstrated that the strongly AF-coupled SyAF with aspect ratio k=1 creates size-independent H-sw down to submicron sizes fabricated, which is understood by zero demagnetization field for k=1 and single domain structure, observed by MFM. The size-independent switching field demonstrates the predominance of the SyAF for spintronics devices, requiring a low switching field and stabilized single domain structure for small bit sizes such as ultrahigh density magnetic random access memories and spin transistors. (C) 2003 American Institute of Physics.

  156. Large tunneling magnetoresistance at room temperature using a Heusler alloy with the B2 structure 査読有り

    K Inomata, S Okamura, R Goto, N Tezuka

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 42 (4B) L419-L422 2003年4月

    出版者・発行元:INST PURE APPLIED PHYSICS

    DOI: 10.1143/JJAP.42.L419  

    ISSN:0021-4922

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    A Co2Cr0.6Fe0.4Al Heusler alloy film exhibited a B2 structure, which,was deposited using a magnetron sputtering system on a, thermally oxidized Si substrate at room temperature without any buffer layers. The film exhibited the magnetic moment of 2.04mu(B) per formula unit, nearly the integer number of Bohr magnetons, suggesting a localized nature of ferromagnetisin similar to that of many Heusler compounds, which is a necessary condition for half metallicity. A spin- valve-type tunneling junction with a Co-2(Cr, Fe)Al Heusler alloy film was fabricated using metal masks, which consists Of Co2Cr0.6Fe0.4Al(10 nm)/AlOx (1.8 nm)/CoFe (3 nm)/NiFe (5 nm)/IrMn (15 nm)/Ta (5 nm), deposited on a thermally oxidized Si substrate without a buffer layer. The junction demonstrated large tunneling magnetoresistances of 16% at room temperature and 26.5% at 5K.

  157. ZnxFe3-xO4薄膜の構造および磁気・電気特性 査読有り

    西村和正, 手束展規, 猪俣浩一郎, 杉本諭

    日本応用磁気学会誌 27 (4) 340-343 2003年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.27.340  

    ISSN:0285-0192

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    The structural, magnetic, and electrical properties of sputtered Zn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub> thin films were investigated. A spinel structure was obtained for samples annealed above 673 K. The magnetization at 10 kOe of a sample sputtered in Ar and annealed at 873 K was 450 emu/cm<sup>3</sup>. Magnetization decreased in samples annealed above 873 K, as a result of evaporation of Zn and an increase in the thickness of the insulating layer. A MR ratio of about 4.3 % was observed at T = 300 K in a sample sputtered in Ar and O<sub>2</sub> mixed gas, and MR curve was of a granular type. However, because the Zn was completely evaporated at this sample, the MR was associated with the Fe<sub>3</sub>O<sub>4</sub> grains and the α-Fe<sub>2</sub>O<sub>3</sub> boundary.

  158. 微細反平行結合素子の磁化状態とスピン反転磁場 査読有り

    小池伸幸, 手束展規, 猪俣浩一郎, 杉本諭

    日本応用磁気学会誌 27 (4) 316-319 2003年

    出版者・発行元:公益社団法人 日本磁気学会

    DOI: 10.3379/jmsjmag.27.316  

    ISSN:0285-0192

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    Arrays of synthetic antiferromagnetic (SyAF) patterned elements were successfully fabricated with micron to submicron sizes. Their magnetic domain structures and spin-switching fields were investigated by using magnetic force microscopy (MFM) and the magnetic optical Kerr effect (MOKE), respectively. A single-domain structure was observed in Co<sub>9</sub>Fe/Ru/Co<sub>9</sub>Fe SyAF bits for even a small aspect ratio of 1, while Co<sub>9</sub>Fe monolayer bits showed a multi-domain structure for aspect ratios below 2. The spin-switching field of Co<sub>9</sub>Fe (6 nm)/Ru (0.45 nm)/Co<sub>9</sub>Fe (10 nm) SyAF exhibited independence of element size, while that of Co<sub>9</sub>Fe (10 nm) single elements was strongly dependent on element size. These results indicate the predominance of SyAF for ultrahigh-bit-density MRAM devices.

  159. ピン層にCoFe/CoFeOx/CoFeを用いた強磁性トンネル接合の耐熱性の改善 査読有り

    落合隆夫, 手束展規, 猪俣浩一郎, 杉本諭, 斉藤好昭

    日本応用磁気学会誌 27 (4) 307-310 2003年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.27.307  

    ISSN:0285-0192

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    The annealing temperature dependence of the tunnel magnetoresistance (TMR) ratio for ferromagnetic tunnel junctions with CoFeO<sub>x</sub> inserted in the pinned layer was investigated. A junction with a CoFe/CoFeO<sub>x</sub>/CoFe as the pinned layer exhibited TMR ratios of 47 % and 43 % after annealing at 350°C and at 375°C respectively, The reason for the improvement of the thermal stability is related to oxygen diffusion from CoFeO<sub>x</sub> layer, and there is a possibility that CoFeO<sub>x</sub> plays a role of Mn (in MnIr exchange layer) diffusion barrier.

  160. Single domain observation for synthetic antiferromagnetically coupled bits with low aspect ratios 査読有り

    N Tezuka, N Koike, K Inomata, S Sugimoto

    APPLIED PHYSICS LETTERS 82 (4) 604-606 2003年1月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1539549  

    ISSN:0003-6951

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    Arrays of the synthetic antiferromagnetic (SyAF) patterned bits were successfully fabricated with micron to submicron sizes. Magnetic domain structure was investigated using magnetic force microscopy (MFM) for the SyAF bits as well as monolayer bits. MFM image of Co90Fe10(10 nm)/Ru(0.6 nm)/Co90Fe10(6 nm) SyAF bits demonstrates single domain structure for even a small aspect ratio of 1, while the 10 nm Co90Fe10 monolayer bits showed multi-domain structure for the aspect ratios below 2. This result indicates the predominance of the SyAF for ultrahigh bit density magnetic random access memory devices, because the bits with aspect ratio of 1 possessing single domain structure can provide size-independent switching field. (C) 2003 American Institute of Physics.

  161. Magnetic switching field and giant magnetoresistance effect of multilayers with synthetic antiferromagnet free layers 査読有り

    K Inomata, T Nozaki, N Tezuka, S Sugimoto

    APPLIED PHYSICS LETTERS 81 (2) 310-312 2002年7月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.1490149  

    ISSN:0003-6951

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    Synthetic antiferromagnets (SyAF) made of Co90Fe10(t(1))/Ru(d)/Co90Fe10(t(2)) trilayers and spin-valve type multilayers using a SyAF free layer were deposited on a buffer layer of Cu(2.5 nm)/Ru(10 nm) on a SiO2/Si substrate by using an ultrahigh vacuum sputtering system and a metal mask. The magnetization switching field of the SyAF in both trilayers and multilayers was independent of the Ru thickness, suggesting that the switching field is independent of the magnitude of the antiferromagnetic interlayer exchange coupling, and was proportional to t(1)/Deltat (Deltat=parallel tot(1)-t(2)parallel to), which is in good agreement with the model of coherent rotation with perfect antiparallel alignment during magnetization reversal of the SyAF. Giant magnetoresistance of the multilayers exhibited two types of curves depending on t(1)&gt;t(2) or t(1)&lt;t(2). (C) 2002 American Institute of Physics.

  162. A thermodynamic study of the HDDR conditions in the Sm2Fe17Nx compound 査読有り

    S Ohga, S Sugimoto, N Tezuka, T Kagotani, K Inomata

    MATERIALS TRANSACTIONS 43 (3) 459-461 2002年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.43.459  

    ISSN:1345-9678

    eISSN:1347-5320

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    This paper describes the relationship between hydrogen pressure and temperature ( P-T curve) in the HDDR treatment of the SM2Fe17 compound. The P-T curve suggested that the HDDR condition of the SM2Fe17 compound is more sensitive to temperature than that of the Nd2Fe14B compound. It was also found that the HDDR treatment of the Sm2Fe17 compound has to be controlled in the hydrogen pressure range of one order lower than that of the Nd2Fe14B compound. because of its lower optimum HDDR temperature. Using the P-T curve, new HDDR treatments named v-HD and s-DR, were carried out in order to induce anisotropic feature. However, the normalized remanence of the new HDDR treated powders was around 0.52, which suggested that the powders were almost magnetically isotropic.

  163. Magnetic properties and microwave absorption properties of polymer-protected cobalt nanoparticles 査読有り

    Y Kato, S Sugimoto, K Shinohara, N Tezuka, T Kagotani, K Inomata

    MATERIALS TRANSACTIONS 43 (3) 406-409 2002年3月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.43.406  

    ISSN:1345-9678

    eISSN:1347-5320

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    This paper describes magnetic properties and microwave absorption proper-ties of polymer-protected cobalt nanoparticles. Cobalt nanoparticles were prepared using the thermal decomposition of dicobalt octacarbonyl in ethylene glycol. They were stabilized and dispersed by coexisting with poly(N-vinyl-2-pyrrolidone) (PVP), resulting in an average diameter of 45 nm. The X-ray diffraction (XRD) analysis revealed that the Co-PVP sample synthesized at 170degreesC for 3 h, with the mole ratio of cobalt : PVP = 1 : 10 (mol : unit mole), consisted of two phases of hcp and fcc cobalt, Their saturation magnetization measured using a vibrating sample magnetometer (VSM) was 1.53 x 10(-4) Wb.m.kg(-1). The compacted sample, produced from the PVP-protected cobalt nanoparticles. showed a reflection loss (R.L.) less than -20 dB at the frequency (matching frequency: f(m)) of 0.54 and 0.64 GHz with the thickness (matching thickness: d(m)) of 6.16 and 5.04 mm, respectively. Therefore. it is Concluded that polymer-protected cobalt nanoparticles have a possibility for the use as microwave absorption materials.

  164. Magnetic properties of the Cr(001) surface studied by spin-polarized scanning tunneling spectroscopy 査読有り

    M Kleiber, M Bode, R Ravlic, N Tezuka, R Wiesendanger

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 240 (1-3) 64-69 2002年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    ISSN:0304-8853

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    The magnetic properties of the Cr(0 0 1) surface have been studied by spin-polarized scanning tunneling spectroscopy (SP-STS). Spatially resolved mapping of the spectroscopic dI/dU signal at an energy close to the spin-polarized Cr(0 0 1) surface state allows the confirmation of the topological antiferromagnetic order of the Cr(0 0 1) surface, It is shown that the presence of screw dislocations leads to the formation of domain walls which. exhibit a width of 120-170 rim. A long-period modulation of the SP-STS signal was not observed indicating that the bulk spin-density wave is modified at the surface due to symmetry breaking. (C) 2002 Elsevier Science B.V. All rights reserved.

  165. Improvement of coercivity of anisotropic Nd-Fe-BHDDR powders by Ga addition 査読有り

    S Sugimoto, H Murai, N Koike, H Nakamura, D Book, N Tezuka, T Kagotani, M Okada, M Homma, K Inomata

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 239 (1-3) 444-446 2002年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(01)00620-5  

    ISSN:0304-8853

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    The effect of Ga addition on the increase of coercivity of HDDR-treated Nd-Fe-B powders was investigated, The Ga addition suppresses grain growth and may decrease the region where magnetocrystalline anisotropy is reduced. In addition, a heat treatment in which the hydrogen pressure was decreased in steps during the recombination reaction resulted in good magnetic properties of B-1 = 1.44T,H-3(c) = 0.97 MA m(=1) and (BH)(max) = 308 kH m(-3), (C) 2002 Elsevier Science B.V. All rights reserved.

  166. Switching field behavior in antiparallely coupled sub-micrometer scale magnetic elements 査読有り

    N Tezuka, E Kitagawa, K Inomata, S Sugimoto, N Kikuchi, Y Shimada

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 240 (1-3) 294-296 2002年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(01)00782-X  

    ISSN:0304-8853

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    Magnetization process and switching field of sub-micron sized elements for antiparallely coupled ferromagnetic systems (ferromagnet/nonmagnet/ferromagnet) are studied with micromagnetic simulation using Landau-Lifshiz-Gilbert equations. It is found that the switching field of the antiparallel structure of the trilayer is lower than that of the ferromagnetic single film for above aspect ratio = 2 and below width = 150 nm. (C) 2002 Elsevier Science B.V. All rights reserved.

  167. 反平行結合フリー層を用いたGMRスピンバルブ膜の磁化反転特性 査読有り

    野崎隆行, 阿部慎也, 手束展規, 猪俣浩一郎, 杉本諭

    日本金属学会誌 66 1078-1082 2002年

    DOI: 10.2320/jinstmet1952.66.11_1078  

  168. Thickness and Oxidation Time Dependence of Tunnel Magnetoresistance in Ni-Fe/Co/Al-O/Co Junctions 査読有り

    H. Kubota, S. Otsuka, M. Kamijo, N. Tezuka, Y. Ando, C.C. Yu, T. Miyazaki

    Journal of the Magnetics Society of Japan 24 (4) 595-598 2000年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.24.595  

    ISSN:0285-0192

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    Ni-Fe/Co/Al-O/Co tunnel junctions with small active areas down to 3 x 3 μm<sup>2</sup> were fabricated by the micro-fabrication technique. The Al-O insulating layer was prepared by plasma oxidation of a thin sputtered Al film. The dependences of the tunnel magnetoresistance on the thickness of the Al film and the oxidation time were investigated. The interface structure of the junction was observed by using high-resolution electron microscopy. The relationship between the magnetoresistive properties and the interface structure is discussed.

  169. Characterization of the Barrier Layer in Al1-xCox/{ Al1-xCox -Oxide}/Al Tunnel Junctions 査読有り

    X.F. Han, J. Murai, M. Hayashi, N. Tezuka, Y. Ando, T. Miyazaki

    Journal of the Magnetics Society of Japan 24 (4) 603-606 2000年

    出版者・発行元:公益社団法人 日本磁気学会

    DOI: 10.3379/jmsjmag.24.603  

    ISSN:0285-0192

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    Oxides of Al<sub>1-x</sub>Co<sub>x</sub> (x = 0, 0.25, 0.50, 0.75, and 1.0) alloys were chosen as barrier materials in this work. The tunnel junctions consisted of a bottom electrode Al<sub>1-x</sub>Co<sub>x</sub> and a top electrode Al with an insulating layer {Al<sub>1-x</sub>Co<sub>x</sub>-oxide} formed by natural oxidation in a baking-box at 333 K. The oxidation time for forming an Al<sub>1-x</sub>Co<sub>x</sub>-oxide layer on the surface of the bottom Al<sub>1-x</sub>Co<sub>x</sub> layers was optimized. When tunnel resistances were between 10<sup>5</sup> and 10<sup>7</sup> &Omega;&mu;m<sup>2</sup> measured at 1 mV and at 4.2 K, the effective barrier height and width of the insulating layers of Al<sub>1-x</sub>Co<sub>x</sub>-oxide (x = 0.25, 0.5, and 0.75) varied between 0.7 and 2.2 eV and between 1.4 and 1.7 nm, respectively. It is shown that the thin oxide layer of Al<sub>1-x</sub>Co<sub>x</sub> alloys can be used as a barrier.

  170. Ni80Fe20/Co/N(N=Ta,Cu,Al)/Al-oxide/Co接合における磁気抵抗効果 査読有り

    大坊忠臣, 手束展規, 久保田均, 安藤康夫, 林将光, 宮崎照宣, Changkyung Kim, Ohsung Song

    日本応用磁気学会誌 24 (4) 599-602 2000年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.24.599  

    ISSN:0285-0192

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    The effect on the tunneling magnetoresistance (TMR) of inserting the nonmagnetic metals (NMs) Al, Cu, and Ta between the insulator and ferromagnetic layer of a tunnel junctions was investigated. The TMR ratio for a junction with Ta decreased rapidly with increasing Ta thickness, while that for a junction with Al remained more than 50 Å of the thickness. From cross-sectional TEM and AFM measurement, it was found that a junction with thick Al has an insulating layer on both sides of the metallic Al; that is, it would be a double-barrier tunnel junction. We compared the experimental result for the metallic Al thickness dependence of the TMR ratio with the theory of double tunnel junctions. Consequently, the spin diffusion length of Al was estimated to be sub-micrometer.

  171. Applied voltage and temperature dependence of tunneling magnetoresistance 査読有り

    N Tezuka, M Oogane, T Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 198-99 149-151 1999年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(98)01056-7  

    ISSN:0304-8853

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    The dependence of tunnel magnetoresistance (TMR) ratio on temperature and applied voltage has been studied for Fe/Al-oxide/Fe and 80NiFe/Al-oxide/Co junctions. Their dependence for an Fe/Al-oxide/Fe junction is greater than that for a 80NiFe/Al-oxide/Co junction. The rapid decrease of TMR ratio with increasing temperature for the Fe/Al-oxide/Fe junction below 100 K or 10 mV and small decrease below about 40 K for the 80NiFe/Al-oxide/Co junction can be explained by the spin flip scattering due to magnetic impurities. (C) 1999 Elsevier Science B.V. All rights reserved.

  172. Influence of interlayer roughness on magnetoresistive effect of ferromagnetic tunneling junctions 査読有り

    Y Ando, M Yokota, N Tezuka, T Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 198-99 155-157 1999年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(98)01053-1  

    ISSN:0304-8853

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    Ferromagnetic tunneling 80NiFe/Co/Al-oxide/Co junctions with wedge shaped Al-oxide were fabricated. For preparing Al-oxide, pure Al was sputtered without exposure. The tunnel resistance for junctions with sufficiently oxidized Al increased exponentially with increasing d(Al) On the other hand, the tunnel resistance for junctions with an air-leak scattered. The tunneling magnetoresistive effect (TMR) was observed at about 7 Angstrom Al for junctions without exposure. The surface roughness of the sample without exposure was quite small, while that with an air-leak tended to be large with increasing oxidization time and also d(Al). The corresponding tunnel resistance was very small for the junction with the rough interface. (C) 1999 Elsevier Science B.V. All rights reserved.

  173. Arイオンミリングによる強磁性トンネル接合の微細加工 査読有り

    大塚茂樹, 上條誠, 手束展規, 久保田均, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1305-1308 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1305  

    ISSN:0285-0192

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    The effect of the Ar ion milling process on tunnel magneto-resistance was investigated by using Ar ion milling to make a small hole at the center of the active area of a junction prepared by means of metal masks. Metallic short-circuiting through the material redeposited during Ar ion milling was evaluated by comparing the tunnel resistance before and after the process. The amount of redeposited material was small in the samples produced by the milling process with a higher incident angle of Ar ions. Small Ni-Fe/Co/Al-O/Co junctions with various active area ranged from 9 to 10<sup>4</sup> μm<sup>2</sup> were also fabricated. The tunnel resistance increased in inverse proportion to the active area. Many junctions showed a TMR ratio of 9%-13%, which was as large as the value for junctions prepared by means of metal masks.

  174. 強磁性体/Al-Oxide/Co接合のトンネル磁気抵抗効果の印加電圧及び温度依存性 査読有り

    大兼幹彦, 手束展規, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1297-1300 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1297  

    ISSN:0285-0192

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    Ferromagnetic tunneling junctions with various thicknesses of the first ferromagnetic layer were fabricated. Co and Ni<sub>80</sub>Fe<sub>20</sub> were used as the first ferromagnetic layer, and their thicknesses were varied between 10 and 200 Å. The voltage and temperature dependence of the tunneling magnetoresistance (TMR) ratio and conductance characteristic were investigated for these junctions. A drastic decrease in the conductance near the zero bias in the conductance-voltage characteristics (zero-bias anomaly) was observed in some junctions. A rapid decrease in the TMR ratio below 5 mV and 50 K was also observed in the same junctions. A slight decrease in the TMR ratio above 10 mV and 100 K was observed in all junctions. We investigated the origin of the voltage and temperature dependence of the TMR ratio by taking account of the magnetic impurity and magnon effect.

  175. Ni80Fe20/Al-Oxide/Co接合におけるトンネル磁気抵抗比のNi80Fe20膜厚依存性 査読有り

    大兼幹彦, 手束展規, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1309-1312 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1309  

    ISSN:0285-0192

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    Ferromagnetic tunneling junctions with various thicknesses of the first ferromagnetic layer were fabricated. Ni<sub>80</sub>Fe<sub>20</sub> and Co were used as the first ferro-magnetic layer, and their thicknesses were varied between 10 and 200 Å. The tunneling magnetoresistance (TMR) ratio decreased and the shape of the TMR curve changed with decreasing Ni<sub>80</sub>Fe<sub>20</sub> thickness, but changed only slightly with decreasing Co thickness. We calculated the TMR and magnetization curves by using a simple model that takes account of magnetic anisotropy to explain the change in the TMR ratio and the shape of the TMR curve with changing Ni<sub>80</sub>Fe<sub>20</sub> thickness.

  176. Ni80Fe20/Al-oxide/Co接合における磁気抵抗効果のAl-oxide厚依存性 査読有り

    手束展規, 宮崎照宣

    日本応用磁気学会誌 23 (4) 1317-1320 1999年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.23.1317  

    ISSN:0285-0192

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    Ferromagnetic tunneling junctions of Ni<sub>80</sub>Fe<sub>20</sub>/Al oxide/Co with various Ni<sub>80</sub>Fe<sub>20</sub> and Al-oxide thicknesses were fabricated by magnetron sputtering using metal masks. The thicknesses of Ni<sub>80</sub>Fe<sub>20</sub> were 70, 100, 200, 500, and 1000 Å. The thicknesses of the Al layer ranged from 7 to 80 Å, and the Al oxide films were formed by natural oxidization. The thicker the Ni<sub>80</sub>Fe<sub>20</sub> layer, the larger the optimum Al thickness for the TMR ratio. On the other hand, when the thickness of Ni<sub>80</sub>Fe<sub>20</sub> was constant, the TMR ratio decreased with increasing Al thickness. To clarify the reason for this, AFM images of the Ni<sub>80</sub>Fe<sub>20</sub> surface were measured. The surface roughness of Ni<sub>80</sub>Fe<sub>20</sub> increased with increasing Ni<sub>80</sub>Fe<sub>20</sub> thickness.

  177. Spin-polarized magnetic tunnelling magnetoresistive effects in various junctions 査読有り

    T Miyazaki, N Tezuka, S Kumagai, Y Ando, H Kubota, J Murai, T Watabe, M Yokota

    JOURNAL OF PHYSICS D-APPLIED PHYSICS 31 (6) 630-636 1998年3月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0022-3727/31/6/009  

    ISSN:0022-3727

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    Recent progress concerning spin-polarized magnetic tunnelling effects for (i) trilayer standard ferromagnet (F)/insulator (I)/ferromagnet (F) junctions, (ii) spin-valve-type junctions, (iii) trilayer or multilayer ferromagnet/granular/ferromagnet junctions and (iv) F/I/F junction with a 'wedge-geometry' insulator is reviewed. Special emphasis is placed on the dependence of the tunnel magnetoresistance ratio on temperature and also the intensity of the applied voltage. It was found that the resistiance for the saturation magnetization state, R-S, and the tunnelling magnetoresistance ratio, TMR, of an Fe/Al(2)O3/Fe junction decreased rapidly with increasing temperature, whereas those of a NiFe/Al2O3/Co junction were insensitive to temperature. Concerning the bias voltage dependence of Rs and TMR, the same tendency with temperature was observed for Fe/Al2O3/Fe and NiFe/Al2O3/Co junctions. Spin-valve-type junction exchange biased by a FeMn layer exhibits a relatively large TMR ratio up to about 400 K.

  178. Barrier height dependence of MR ratio in Fe/Al-oxide/Fe junctions 査読有り

    N Tezuka, T Miyazaki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 177 1283-1284 1998年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0304-8853(97)00964-5  

    ISSN:0304-8853

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    The magnetic tunneling effect has been investigated for Fe/Al-oxide/Fe junctions to clarify the relationship between magnetoresistance (MR) ratio and barrier height of ferromagnetic tunneling junctions. The MR ratio measured at 4.2 K and 0.5 mV varied from about 0.5% to 30% depending on barrier height. The barrier height dependence of MR ratio at 4.2 K was roughly the same as that of Slonczewski's calculation. (C) 1998 Elsevier Science B.V. All rights reserved.

  179. Temperature and Applied Voltage Dependence of Magnetoreisitance Ratio in Fe/Al oxide/Fe Junctions 査読有り

    Nobuki Tezuka, Terunobu Miyazaki

    Japanese Journal of Applied Physics 37 L218-L220 1998年

    DOI: 10.1143/JJAP.37.L218  

  180. ウェッジ状のAl-O絶縁層を有する強磁性トンネル接合の磁気抵抗効果 査読有り

    横田匡史, 安藤康夫, 手束展規, 宮崎照宣

    日本応用磁気学会誌 22 (4) 569-572 1998年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.22.569  

    ISSN:0285-0192

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    Ferromagnetic tunneling junctions of Ni<sub>80</sub>Fe<sub>20</sub> (Py)/Co/Al oxide/Co with wedge-shaped insulators were fabricated. Al oxide films were formed by natural oxidization with various conditions and were checked by FT-IR spectroscopy. The peak intensity and the position depending on the Al thickness were explained by using the 1-D Einstein model. When the oxidization time was less than 50 h, tunneling magnetoresistance (TMR) was observed at about 13 Å of the Al thickness. When the oxidization time became more than 50 h, the thickness shifted to less than 10 Å. The reason for this was considered that Co oxide was formed on the surface of the bottom electrode and became a tunneling barrier with increasing oxidization time. On the other hand, the TMR decreased rapidly with increasing Al thickness. To determine the reason for this, AFM images of the Py/Co/Al surface with various oxidization times were measured. The surface roughness of the Al increased with increasing oxidization time, corresponding to the TMR results.

  181. 非弾性電子トンネル分光法(IETS)を用いた強磁性体/絶縁体界面の解析 査読有り

    村井純一郎, 安藤康夫, 手束展規, 宮崎照宣

    日本応用磁気学会誌 22 (4) 573-576 1998年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.22.573  

    ISSN:0285-0192

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    Inelastic electron-tunneling spectroscopy (IETS) has been used to investigate the vibrational spectrum in Al/Al<sub>2</sub>O<sub>3</sub>/CO/AI tunneling junctions with various Co thicknesses (<i>d</i> <sub>Co</sub>). A zero-bias anomaly was observed in the conductance curve of the junction with <i>d</i><sub>Co</sub> of 2Å, and decreased with increasing <i>d</i><sub>Co</sub>. The IET spectra of these junctions showed strong negative peaks at 4 mV, corresponding to the zero-bias anomaly, while phonon spectra were observed for the junction with <i>d</i><sub>Co</sub> ≥ 10Å. The peak position was different from that of Al/Al<sub>2</sub>O<sub>3</sub>/Al. After annealing of the junction with <i>d</i><sub>Co</sub> of 2Å at 250°C for one hour, the zero-bias anomaly decreased and the phonon spectrum appeared.

  182. NiFe/Co/Al2O3/Co/NiFe/FeMn接合のトンネル磁気抵抗効果 査読有り

    熊谷静似, 手束展規, 宮崎照宣

    日本応用磁気学会誌 22 (4) 561-564 1998年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.22.561  

    ISSN:0285-0192

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    Spin-valve-type ferromagnetic tunneling junctions using contact metal masks were fabricated, and the annealing effect and temperature dependence of the tunneling magnetoresistance (TMR) ratio and saturated resistance (<i>R</i><sub>s</sub>) were investigated. As-prepared NiFe/Co/Al<sub>2</sub>O<sub>3</sub>/Co/NiFe/FeMn junctions showed a spin-valve-like MR curve at room temperature. The effect of field annealing was investigated for two reasons: to increase the TMR ratio and: to create an orthogonal magnetic orientation in each of the two magnetic layers. The temperature dependence of the TMR ratio and <i>R</i><sub>s</sub> is affected by the annealing. For the annealed junction, the TMR ratio decreases slightly with increasing temperature and decreases rapidly around 418 K, because of the disappearance of the exchange bias in the FeMn layer.

  183. Spin-polarized tunneling magnetoresistive effect in ferromagnet/insulator/ferromagnet junctions 査読有り

    T Miyazaki, N Tezuka, S Kumagai

    PHYSICA B 237 256-260 1997年7月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0921-4526(97)00152-X  

    ISSN:0921-4526

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    Current status on the study of spin-polarized tunneling magnetoresistive effect was reviewed. Special emphasis was placed on the tunneling barrier height dependence of magnetoresistance ratio and interlayer exchange coupling in the microstructured junctions made by photolithography.

  184. 強磁性トンネル接合における絶縁障壁と磁気抵抗 査読有り

    手束展規, 安藤康夫, 宮崎照宣, H.G. Tompkins, S. Tehrani, H. Goronkin

    日本応用磁気学会誌 21 (4) 493-496 1997年

    出版者・発行元:The Magnetics Society of Japan

    DOI: 10.3379/jmsjmag.21.493  

    ISSN:0285-0192

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    The dependence of the tunneling magnetoresistive effect on the barrier height was investigated. The magnitude of the barrier height increased with increasing aluminum oxidation temperature and time from 0.3 to 2.3 eV in Fe/Al oxide/Fe junctions. However, those values are smaller than those reported for an Al<sub>2</sub>O<sub>3</sub> barrier. A possible reason for this is that the barrier is not pure Al<sub>2</sub>O<sub>3</sub>, but AIO<sub><i>x</i></sub>, or another oxide created by interface mixing between Fe and Al oxide. On the other hand, the magnetoresistance ratio in these junctions varied up to 18% at room temperature and up to 18% at 4.2 K. The dependence of the magnetoresistance ratio at 4.2 K on the barrier height is roughly the same as predicted by Slonczewski's theory. This result shows that the effective spin polarization of ferromagnetic electrodes changes according to the barrier height.

  185. Temperature Dependence of the Spin Tunneling Magnetoresistive Effects on NiFe/Co/Al2O3/Co/NiFe/FeMn Junctions 査読有り

    Seiji Kumagai, Nobuki Tezuka, Terunobu Miyazaki

    Japanese Journal of Applied Physics 36 L1498-L1500 1997年

    DOI: 10.1143/JJAP.36.L1498  

  186. Magnetic tunneling effect in Fe/Al2O3/Ni1-xFex junctions 査読有り

    N Tezuka, T Miyazaki

    JOURNAL OF APPLIED PHYSICS 79 (8) 6262-6264 1996年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.362028  

    ISSN:0021-8979

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    The dependence of the magnetoresistance ratio, Delta R/R(s), on the Ni content has been studied in Fe/Al2O3/Ni1-xFex (0 less than or equal to x less than or equal to 1) tunneling junctions. The value of Delta R/R(s) at 4.2 K increased with increasing x and exhibited a maximum of similar to 35% at x = 0.8. The result is discussed by taking into account the spin-polarization of ferromagnetic electrodes. (C) 1996 American Institute of Physics.

  187. Spin polarized tunneling in ferromagnet insulator ferromagnet junctions 査読有り

    T Miyazaki, N Tezuka

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 151 (3) 403-410 1995年12月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/0304-8853(95)00563-3  

    ISSN:0304-8853

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    Experimental data and theoretical explanation reported for spin polarized tunneling in ferromagnet/insulator/ferromagnet are reviewed. The magnetoresistance (MR) ratio due to the spin polarized tunneling is relatively smaller value than that of giant magnetoresistance in artificial superlattices. However, recent results reported by us are an order of magnitude larger than those reported in the past. We demonstrate that the magnetoresistance ratio is roughly proportional to the product of spin polarizations of both ferromagnets. The dependence of MR ratio, saturation resistance and conductance on temperature are also discussed.

  188. Giant magnetic tunneling effect in Fe/Al2O3/Fe junction 査読有り

    T. Miyazaki, N. Tezuka

    Journal of Magnetism and Magnetic Materials 139 L231-L234 1995年

    DOI: 10.1016/0304-8853(95)90001-2  

  189. 強磁性/Al2O3/強磁性接合の磁気トンネリング効果 査読有り

    手束展規, 安藤康夫, 宮崎照宣

    日本応用磁気学会誌 19 369-372 1995年

    DOI: 10.3379/jmsjmag.19.369  

  190. Fe,Ni,Co金属の結晶粒径と保磁力 査読有り

    佐藤文隆, 手束展規, 桜井伴明, 宮崎照宣

    日本応用磁気学会誌 17 886-891 1993年

    DOI: 10.3379/jmsjmag.17.886  

︎全件表示 ︎最初の5件までを表示

共同研究・競争的資金等の研究課題 3

  1. 高性能永久磁石に関する研究 競争的資金

    2000年9月 ~ 継続中

  2. 高周波磁性材料の開発 競争的資金

    2000年9月 ~ 継続中

  3. スピントランスポートデバイスに関する研究 競争的資金

    制度名:The Other Research Programs

    1994年4月 ~ 継続中

社会貢献活動 3

  1. イノベーションジャパン

    2004年9月28日 ~ 2004年9月30日

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    最新の研究成果を一般に広く伝え,専門外の人たちにも研究成果を共通の知識としてもらうことに協力

  2. リフレッシュ理科教室

    2001年8月6日 ~ 2001年8月7日

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    小・中学生,ならびに,先生に理科の面白さを知ってもらい,現場の先生方に基礎から最新の科学技術までを知る機会を提供

  3. 東北大学サイエンスカフェ

    2007年7月30日 ~

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    一般市民と研究者が,コーヒーカップを片手にサイエンスについて気軽に話し合い,サイエンスの楽しさと社会貢献の姿を知ってもらう場に協力.

その他 3

  1. 高スピン分極材料を用いた高出力磁気利用センサの開発

    詳細を見る 詳細を閉じる

    高スピン分極材料を開発し,磁気利用センサの高性能化を試みる

  2. 反平行結合膜を用いたナノサイズCPP-GMR素子の高再生出力に関する研究

    詳細を見る 詳細を閉じる

    反平行結合膜をフリー層に用いた,CPP-GMR素子の再生出力増大に関する研究.

  3. 低磁界・低電力駆動サブミクロン磁性素子の開発

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    サブミクロン磁性素子の低磁界磁化反転に関する研究