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Masakiyo Tsunoda

Section

Green Goals Initiative

Job title

Professor

Degree

博士(工学) (Tohoku University)

researchmap

https://researchmap.jp/read0180277

J-GLOBAL ID

200901082040310236

Committee Memberships 16

日本磁気学会　論文委員

2009/05 - Present
日本磁気学会　論文委員

2009/05 - Present
日本磁気学会　論文賞・内山賞選考委員

2013/06 - 2014/05
日本磁気学会　論文賞・内山賞選考委員

2013/06 - 2014/05
SPring-8 先端磁性材料研究会　代表

2009/03 - 2010/09
SPring-8 先端磁性材料研究会　代表

2009/03 - 2010/09
日本磁気学会表彰委員会　委員

2009/06 - 2010/05
日本磁気学会表彰委員会　委員

2009/06 - 2010/05
日本応用磁気学会　企画委員

2007/05 - 2009/04
日本応用磁気学会　企画委員

2007/05 - 2009/04
日本応用磁気学会　論文賞・内山賞選考委員

2007/04 - 2009/03
日本応用磁気学会　論文賞・内山賞選考委員

2007/04 - 2009/03
日本応用磁気学会企画委員　企画委員

2001/04 - 2005/03
日本応用磁気学会企画委員　企画委員

2001/04 - 2005/03
2009年度第17回 SPring-8 施設公開　科学講演会講師

2009/04 -
2009年度第17回 SPring-8 施設公開　科学講演会講師

2009/04 -

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Professional Memberships 4

日本真空協会
日本金属学会
The Japan Society of Applied Physics
日本応用磁気学会

Research Areas 1

Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering /

Awards 8

The 25th Outstanding Paper Award

2020/01　The Physical Society of Japan　Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe4N, and Half-Metallic Ferromagnet: A Systematic Analysis; J. Phys. Soc. Jpn. 79, 083711 (2010)
日本磁気学会論文賞

2015/09/09　日本磁気学会　Dependence of Magnetic Damping on Temperature and Crystal Orientation in Epitaxial Fe4N Thin Films
MSJ Distinguished Paper Award

2010/09/05　日本磁気学会　γ-Mn-Ir/Fe-Co-Ni積層膜の交換磁気異方性と強磁性層結晶構造との相関
MSJ Outstanding Research Award

2009/09/13　日本磁気学会　高性能交換磁気異方性材料の研究
MSJ Presentation Award

2006/11/22　日本応用磁気学会　"L12-Mn3X(X=Ir, Rh, Ru) / Co-Fe積層膜の交換磁気異方性"
MSJ Presentation Award

2004/11/29　（社）日本応用磁気学会　Al-N絶縁層を有するトンネル接合膜のTMR特性に及ぼす窒化種の影響
原田研究奨励賞

1999/11/04　財団法人金属研究助成会　極清浄雰囲気中で作製したスピンバルブ型GMR薄膜の微細構造と磁気特性に関する研究
MSJ Young Scientist Award

1996/09/21　日本応用磁気学会　薄膜初期成長過程に及ぼす金属シード層の効果

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Papers 245

Theoretical study on in-plane, out-of-plane, and transverse anisotropic magnetoresistance effects for Fe₄N film

Satoshi Kokado, Masakiyo Tsunoda

Japanese Journal of Applied Physics　2025/05/07
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/add5b3 　

ISSN： 0021-4922

eISSN： 1347-4065

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Abstract We theoretically study the in-plane, out-of-plane, and transverse anisotropic magnetoresistance (AMR) effects for Fe$_4$N film. We here use the electron scattering theory with an extrinsic mechanism, in which the conduction electron is scattered into the conduction state and the localized d states by impurities. The in-plane and out-of-plane AMR effects exhibit the negative AMR ratio of the twofold symmetry, while the transverse AMR effect shows the positive AMR ratio of the fourfold symmetry. The calculation results agree qualitatively well with the respective experimental results for Fe$_4$N film. In addition, the peak structures of the AMR ratios reflect probability densities of a current direction of single atomic d states.
Magnetic anisotropy and damping in epitaxial Fe-Co-Ni binary and ternary alloy thin films

Tomoya Ueno, Takafumi Nakano, Masakiyo Tsunoda, Shogo Yamashita, Takayuki Hojo, Mikihiko Oogane

Journal of Magnetism and Magnetic Materials　172841-172841　2025/01
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2025.172841 　

ISSN： 0304-8853
Fabrication of half-metallic Co<inf>2</inf>FeAl<inf>x</inf>Si<inf>1–</inf><inf>x</inf> thin film with small magneto-crystalline anisotropy constant K<inf>1</inf>

Takayuki Hojo, Hiromi Hamasaki, Masakiyo Tsunoda, Mikihiko Oogane

Journal of Magnetism and Magnetic Materials　601　2024/07/01

DOI： 10.1016/j.jmmm.2024.172144 　

ISSN： 0304-8853
Temperature and bias voltage dependences of magnetic tunnel junction with FeAlSi electrode

Shoma Akamatsu, Byung Hun Lee, Yasen Hou, Masakiyo Tsunoda, Mikihiko Oogane, Geoffrey S.D. Beach, Jagadeesh S. Moodera

APL Materials　12　(2)　2024/02/01

DOI： 10.1063/5.0189570 　

eISSN： 2166-532X
Investigation of deterministic and cumulative nature in helicity-dependent optical switching of ferrimagnetic Gd–Fe–Co films

Takuo Ohkochi, Ryunosuke Takahashi, Hidenori Fujiwara, Hirokazu Takahashi, Roman Adam, Umut Parlak, Kohei Yamamoto, Hitoshi Osawa, Masato Kotsugi, Arata Tsukamoto, Hiroki Wadati, Akira Sekiyama, Claus M. Schneider, Masakiyo Tsunoda, Shigemasa Suga, Toyohiko Kinoshita

Journal of Magnetism and Magnetic Materials　171854-171854　2024/02
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2024.171854 　

ISSN： 0304-8853
Enhanced sensitivity and thermal tolerance in tunnel magnetoresistance sensor using Ta-doped CoFeSiB soft magnetic layer

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

Applied Physics Letters　123　(7)　2023/08/14
Publisher: AIP Publishing
DOI： 10.1063/5.0162276 　

ISSN： 0003-6951

eISSN： 1077-3118

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

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

AIP Advances　13　(2)　025005　2023/02/01

DOI： 10.1063/9.0000440 　
Low magnetic damping constant in half-metallic Co2FeAl Heusler alloy thin films grown by molecular beam epitaxy Peer-reviewed

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

AIP Advances　13　(2)　025204　2023/02/01

DOI： 10.1063/9.0000419 　
Compositional dependence of anisotropic magnetoresistance effects in Weyl semimetal Co2MnAl Heusler alloy epitaxial thin films Peer-reviewed

T. Sato, S. Kokado, H. Shinya, M. Tsujikawa, A. Miura, S. Kosaka, T. Ogawa, M. Shirai, M. Tsunoda

Journal of Applied Physics　132　(22)　223907-1-223907-7　2022/12/12
Publisher: AIP Publishing
DOI： 10.1063/5.0128562 　

ISSN： 0021-8979

eISSN： 1089-7550

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Anisotropic magnetoresistance (AMR) effect on a Weyl semimetal Co₂MnAl Heusler alloy was experimentally and theoretically investigated by changing the Co content, the direction of electric current against the crystal axis, and the measurement temperature. The experimentally fabricated Co₂MnAl thin films epitaxially grown on a MgO single-crystal substrate showed the positive AMR ratios independent of the Co content, the direction of electric current, and the measurement temperature. The AMR ratios for the direction of electric current along Co₂MnAl[100] were larger than those along Co₂MnAl[110]. The maximum AMR ratios for Co₂MnAl[100] were 0.576% at 5 K and 0.349% at 300 K for a Co content of 47 at. %, which is close to the stoichiometric composition. Furthermore, the theoretical calculations of AMR ratios based on the s-d scattering process of the electrons at the Fermi energy, including the information on the density of states (DOS) obtained from first-principles calculations, exhibited trends similar to the experimental results. Compared with the AMR results of Co₂MnGa[110], we found that the magnitude relation between the partial DOS of the ε and γ orbitals of the d state of Co atoms determined the sign of the AMR ratios. These results suggest that the AMR effect of Weyl semimetal Co₂MnAl can be elucidated by the s-d scattering process of the electrons.
Magnetic tunnel junctions using epitaxially grown FeAlSi electrode with soft magnetic property

Shoma Akamatsu, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

AIP Advances　12　(7)　075021-075021　2022/07/01
Publisher: AIP Publishing
DOI： 10.1063/5.0094619 　

eISSN： 2158-3226

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Magnetic tunnel junctions (MTJs) with (001)-oriented D0₃-FeAlSi epitaxial films, which have both soft magnetic properties and surface flatness, were fabricated and characterized. A tunnel magnetoresistance (TMR) ratio of 121% was observed, and a relatively low switching field was also confirmed, reflecting the soft magnetic property of FeAlSi. However, the results of the cross-sectional TEM image of the MTJ and the bias dependence of the TMR ratio indicate that the FeAlSi/MgO interface is probably oxidized. Therefore, since an insertion layer at the interface can suppress oxidation and further improve the TMR ratio, MTJs using FeAlSi epitaxial films are promising structures suitable for applications such as MTJ-based magnetic sensors and worthy of further investigation.
Guidelines for attaining optimal soft magnetic properties in FeAlSi films

Shoma Akamatsu, Mikihiko Oogane, Masakiyo Tsunoda, Yasuo Ando

Applied Physics Letters　120　(24)　242406-242406　2022/06/13
Publisher: AIP Publishing
DOI： 10.1063/5.0086322 　

ISSN： 0003-6951

eISSN： 1077-3118

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Nm-order FeAlSi epitaxial films with a partially D0₃-ordered structure were grown on MgO substrates, and ideal soft magnetic properties were obtained. We found that the sign of the magnetocrystalline anisotropy constant K₁ changes with increasing annealing temperature for certain FeAlSi compositions. This is caused by a change in the volume balance of the ordered phases with the annealing process and the point at which K₁ ∼ 0 shifts to the Al-rich concentration as the degree of D0₃-ordering decreases. K₁ was precisely measured by ferromagnetic resonance under the optimal condition, and the value of 1.6 × 10² (erg/cc) was obtained, which is comparable to that of bulk. The uniaxial component of the magnetic anisotropy due to magnetostriction was small, and a fourfold symmetric component due to magnetocrystalline anisotropy was dominant.
Theoretical Study on Anisotropic Magnetoresistance Effects of Arbitrary Directions of Current and Magnetization for Ferromagnets: Application to Transverse Anisotropic Magnetoresistance Effect

Satoshi Kokado, Masakiyo Tsunoda

Journal of the Physical Society of Japan　91　(4)　2022/04/15
Publisher: Physical Society of Japan
DOI： 10.7566/jpsj.91.044701 　

ISSN： 0031-9015

eISSN： 1347-4073
Observation of unconventional spin-polarization induced spin–orbit torque in L1₂-ordered antiferromagnetic Mn₃Pt thin films

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

Applied Physics Express　15　(3)　033002-033002　2022/03/01
Publisher: IOP Publishing
DOI： 10.35848/1882-0786/ac52d7 　

ISSN： 1882-0778

eISSN： 1882-0786

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Abstract Non-collinear antiferromagnets exhibit richer magneto-transport properties compared to nonmagnetic materials due to the topological spin structure they possess, which allows us to manipulate the charge-spin conversion more freely by taking advantage of the chirality. In this work, we explore the unconventional spin–orbit torque of L1₂-ordered Mn₃Pt with a triangular spin structure. We observed an unconventional spin–orbit torque along the x-direction for the (001)-oriented L1₂ Mn₃Pt and found that it has a sign reversal behavior relative to the crystalline orientation. This generation of unconventional spin–orbit torque can be interpreted as stemming from the magnetic spin Hall effect.
Tunnel magnetoresistance in magnetic tunnel junctions with FeAlSi electrode

Shoma Akamatsu, Mikihiko Oogane, Zhenhu Jin, Masakiyo Tsunoda, Yasuo Ando

AIP Advances　11　(4)　2021/04/01
Publisher: American Institute of Physics Inc.
DOI： 10.1063/5.0041571 　

ISSN： 2158-3226
Theoretical study on anisotropic magnetoresistance effect for weak ferromagnets with a crystal field of tetragonal symmetry Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

Materials Today: Proceedings　33　1864-1868　2020/06
Publisher: Elsevier BV
DOI： 10.1016/j.matpr.2020.05.224 　

ISSN： 2214-7853
Large spin signals in n+ -Si/MgO/ Co2Fe0.4Mn0.6Si lateral spin-valve devices Peer-reviewed

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

Journal of Applied Physics　127　(8)　085306-1-085306-8　2020/02
Fabrication and evaluation of highly c-plane oriented Mn3Sn thin films Peer-reviewed

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

AIP Advances　10　015310-1-015310-5　2020/01
Fabrication of soft-magnetic FeAlSi thin films with nm-order thickness for the free layer of magnetic tunnel junction based sensors Peer-reviewed

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

AIP Advances　10　015302-1-015302-4　2020/01
Composition dependence of the secondorder interfacial magnetic anisotropy for MgO/CoFeB/Ta films Peer-reviewed

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

AIP Advances　9　125053-1-125053-5　2019/12
Polycrystalline Co2Fe0.4Mn0.6Si Heusler alloy thin films with high B2 ordering and small magnetic anisotropy for magnetic tunnel junction based sensors Peer-reviewed

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

AIP Advances　9　125036-1-125036-4　2019/12
Effect of second-order magnetic anisotropy on nonlinearity of conductance in CoFeB/MgO/CoFeB magnetic tunnel junction for magnetic sensor devices Peer-reviewed

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

Scientific Reports　9　17018-1-17018-9　2019/11
Composition dependence of exchange anisotropy in PtxMn100−x/CoyFe100-y films Peer-reviewed

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

IEEE Magnetics Letters　10　4505905-1-4505905-5　2019/10
Signs of anisotropic magnetoresistance in Co2MnGa Heusler alloy epitaxial thin films based on current direction Peer-reviewed

T. Sato, S. Kokado, M. Tsujikawa, T. Ogawa, S. Kosaka, M. Shirai, M. Tsunoda

Applied Physics Express　12　(10)　103005-1-103005-5　2019/09
Improvement of Large Anomalous Hall Effect in Polycrystalline Antiferromagnetic Mn3+xSn Thin Films Peer-reviewed

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

IEEE Transactions on Magnetics　55　2501704-1-2501704-4　2019/06
In-plane and perpendicular exchange bias effect induced by an antiferromagnetic D019 Mn2FeGa thin film Peer-reviewed

T. Ogasawara, E. Jackson, M. Tsunoda, Y. Ando, A. Hirohata

Journal of Magnetism and Magnetic Materials　484　307-312　2019/04
Composition dependence of exchange anisotropy in PtxMn1−x/Co70Fe30 films Peer-reviewed

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

Japanese Journal of Applied Physics　58　(4)　043001-1-043001-5　2019/03
Structure and magnetism of c-plane oriented Mn50(Te50-xSbx) epitaxial thin films with NiAs-type structure Peer-reviewed

Y. Ashizawa, S. Saito, M. Tsunoda, M. Takahashi

Journal of Magnetics Society of Japan　43　(2)　21-24　2019/03
Controlled growth and magnetic property of a-plane-oriented Mn3Sn thin films Peer-reviewed

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

AIP Advances　9　035109-1-035109-4　2019/03
Theoretical Study on Anisotropic Magnetoresistance Effects of I // [100], I // [110], and I // [001] for Ferromagnets with a Crystal Field of Tetragonal Symmetry Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

Journal of the Physical Society of Japan　88　(3)　034706-1-034706-17　2019/02
Erratum II: “Twofold and fourfold symmetric anisotropic magnetoresistance effect in a model with crystal field” (Journal of the Physical Society of Japan(2015)84 (094710)Doi:10.7566/JPSJ.84.094710)

Satoshi Kokado, Masakiyo Tsunoda

Journal of the Physical Society of Japan　88　(6)　2019
Publisher: Physical Society of Japan
DOI： 10.7566/JPSJ.88.068001 　

ISSN： 1347-4073 0031-9015
Anomalous Hall effect in polycrystalline Mn3Sn thin films Peer-reviewed

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

Applied Physics Letters　113　(22)　222405-1-222405-5　2018/11
Effects of annealing temperature on sensing properties of magnetic-tunnel-junction-based sensors with perpendicular synthetic antiferromagnetic Co/Pt pinned layer Peer-reviewed

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

Japanese Journal of Applied Physics　57　(11)　110308-1-110308-4　2018/10
Epitaxial L10-MnAl Thin Films With High Perpendicular Magnetic Anisotropy and Small Surface Roughness Peer-reviewed

M. S. Parvin, M. Oogane, M. Kubota, M. Tsunoda, Y. Ando

IEEE Transactions on Magnetics　54　(11)　3401704-1-3401704-4　2018/10
Large negative anisotropic magnetoresistance in Co2MnGa Heusler alloy epitaxial thin films Peer-reviewed

T. Sato, S. Kokado, S. Kosaka, T. Ishikawa, T. Ogawa, M. Tsunoda

Applied Physics Letters　113　(11)　112407-1-112407-5　2018/09
Large exchange coupling field in perpendicular synthetic antiferromagnetic structures with CoPt alloy Peer-reviewed

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

Japanese Journal of Applied Physics　57　(8)　088004-1-088004-3　2018/08

DOI： 10.1063/1.5027768 　
Low magnetic damping and large negative anisotropic magnetoresistance in half-metallic Co2-xMn1+xSi Heusler alloy films grown by molecular beam epitaxy Peer-reviewed

M. Oogane, A. P. McFadden, K. Fukuda, M. Tsunoda, Y. Ando, C. J. Palmstrøm

Applied Physics Letters　1112　(26)　262407-1-262407-5　2018/06
Fourfold symmetric anisotropic magnetoresistance in half-metallic Co2MnSi Heusler alloy thin films Peer-reviewed

M. Oogane, A. P. McFadden, Y. Kota, T. L. Brown-Heft, M. Tsunoda, Y. Ando, C. J. Palmstrøm

Japanese Journal of Applied Physics　57　(6)　063001-1-063001-4　2018/05
Determination of the element-specific complex permittivity using a soft x-ray phase modulator Peer-reviewed

Y. Kubota, Y. Hirata, J. Miyawaki, S. Yamamoto, H. Akai, R. Hobara, Sh. Yamamoto, K. Yamamoto, T. Someya, K. Takubo, Y. Yokoyama, M. Araki, M. Taguchi, Y. Harada, H. Wadati, M. Tsunoda, R. Kinjo, A. Kagamihata, T. Seike, M. Takeuchi, T. Tanaka, S. Shin, I. Matsuda

PHYSICAL REVIEW B　96　(21)　214417-1-214417-6　2017/12

DOI： 10.1103/PhysRevB.96.214417 　

ISSN： 2469-9950

eISSN： 2469-9969
Optical control pf magnetization dynamics in Ge-Fe-Co films with different compositions Peer-reviewed

Takuo Ohkochi, Hidenori Fujiwara, Masato Kotsugi, Hirokazu Takahashi, Roman Adam, Akira Sekiyama, Tetsuya Nakamura, Arata Tsukamoto, Claus M. Schneider, Hiroto Kuroda, Elvis F. Arguelles, Mamoru Sakaue, Hideaki Kasai, Masakiyo Tsunoda, Shigemasa Suga, Toyohiko Kinoshita

APPLIED PHYSICS EXPRESS　10　(10)　103002-1-103002-4　2017/10

DOI： 10.7567/APEX.10.103002 　

ISSN： 1882-0778

eISSN： 1882-0786
L-edge resonant magneto-optical Kerr effect of a buried Fe nanofilm Peer-reviewed

Y. Kubota, M. Taguchi, H. Akai, Sh. Yamamoto, T. Someya, Y. Hirata, K. Takubo, M. Araki, M. Fujisawa, K. Yamamoto, Y. Yokoyama, S. Yamamoto, M. Tsunoda, H. Wadati, S. Shin, I. Matsuda

PHYSICAL REVIEW B　96　(13)　134432-1-134432-6　2017/10

DOI： 10.1103/PhysRevB.96.134432 　

ISSN： 2469-9950

eISSN： 2469-9969
Polarization dependence of resonant magneto-optical Kerr effect measured by two types of figure-8 undulators Peer-reviewed

Y. Kubota, Sh. Yamamoto, T. Someya, Y. Hirata, K. Takubo, M. Araki, M. Fujisawa, K. Yamamoto, Y. Yokoyama, M. Taguchi, S. Yamamoto, M. Tsunoda, H. Wadati, S. Shin, I. Matsuda

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA　220　17-20　2017/10

DOI： 10.1016/j.elspec.2016.11.008 　

ISSN： 0368-2048

eISSN： 1873-2526
Correction to: Anisotropic magnetoresistance effect of a strong ferromagnet: magnetization direction dependence in a model with crystal field: Anisotropic magnetoresistance effect of a strong ferromagnet: magnetization direction dependence in a model with crystal field (physica status solidi (c), (2014), 11, 5-6, (1026-1032), 10.1002/pssc.201300736) Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

Physica Status Solidi (C) Current Topics in Solid State Physics　14　(9)　2017/09/01
Publisher: Wiley-VCH Verlag
DOI： 10.1002/pssc.201700218 　

ISSN： 1610-1642 1862-6351
Magneto-transport properties of pseudo-single-crystal Mn4N thin films Peer-reviewed

Kazuki Kabara, Masakiyo Tsunoda, Satoshi Kokado

AIP ADVANCES　7　(5)　056416-1-056416-6　2017/05

DOI： 10.1063/1.4974065 　

ISSN： 2158-3226
Negative anisotropic magnetoresistance resulting from minority spin transport in NixFe4-xN (x=1 and 3) epitaxial films Peer-reviewed

Fumiya Takata, Kazuki Kabara, Keita Ito, Masakiyo Tsunoda, Takashi Suemasu

JOURNAL OF APPLIED PHYSICS　121　(2)　023903-1-023903-5　2017/01

DOI： 10.1063/1.4974002 　

ISSN： 0021-8979

eISSN： 1089-7550
Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets Peer-reviewed

Satoshi Kokado, Yuya Sakuraba, Masakiyo Tsunoda

JAPANESE JOURNAL OF APPLIED PHYSICS　55　(10)　108004-1-108004-3　2016/10

DOI： 10.7567/JJAP.55.108004 　

ISSN： 0021-4922

eISSN： 1347-4065
Galvanomagnetic Effects of Antiperovskite-Type Transition Metal Nitride Thin Films Peer-reviewed

責任著者, 角田匡清, 共著者, 角田匡清, 鹿原和樹, 古門聡士

まぐね(Magnetics Japan)　11　(3)　125-132　2016/06
Publisher:
ISSN： 1880-7208
Anomalous Hall effects in pseudo-single-crystal gamma '-Fe4N thin films Peer-reviewed

Kazuki Kabara, Masakiyo Tsunoda, Satoshi Kokado

AIP ADVANCES　6　(5)　055801-1-055801-5　2016/05

DOI： 10.1063/1.4942550 　

ISSN： 2158-3226
Transverse anisotropic magnetoresistance effects in pseudo-single-crystal gamma '-Fe4N thin films Peer-reviewed

Kazuki Kabara, Masakiyo Tsunoda, Satoshi Kokado

AIP ADVANCES　6　(5)　055818-1-055818-5　2016/05

DOI： 10.1063/1.4943923 　

ISSN： 2158-3226
Perpendicular magnetic anisotropy in CoxMn4-xN (x=0 and 0.2) epitaxial films and possibility of tetragonal Mn4N phase Peer-reviewed

Keita Ito, Yoko Yasutomi, Kazuki Kabara, Toshiki Gushi, Soma Higashikozono, Kaoru Toko, Masakiyo Tsunoda, Takashi Suemasu

AIP ADVANCES　6　(5)　056201-1-056201-6　2016/05

DOI： 10.1063/1.4942548 　

ISSN： 2158-3226
Enhanced inverse spin-Hall voltage in (001) oriented Fe4N/Pt polycrystalline films without contribution of planar-Hall effect Peer-reviewed

Shinji Isogami, Masakiyo Tsunoda

JAPANESE JOURNAL OF APPLIED PHYSICS　55　(4)　043001-1-043001-5　2016/04

DOI： 10.7567/JJAP.55.043001 　

ISSN： 0021-4922

eISSN： 1347-4065
Magneto-optic effect of Fe based magnetic materials using polarization-modulated soft X-ray source

Kubota Y., Taguchi M., Hirata Y., Hobara R., Yamamoto Sh., Someya T., Yokoyama Y., Yamamoto K., Takubo K., Araki M., Yamamoto S., Miyawaki J., Fujisawa M., Harada Y., Tsunoda M., Wadati H., Shin S., Matsuda I.

Meeting Abstracts of the Physical Society of Japan　71　1273-1273　2016
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.71.2.0_1273 　
Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect in a Model with Crystal Field Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　84　(9)　094710-1-094710-18　2015/09

DOI： 10.7566/JPSJ.84.094710 　

ISSN： 0031-9015
Fabrication of a Current-Perpendicular to Plane Magneto-resistive Device with a Dry Ice Blasting Lift-off Process Peer-reviewed

K. Miyake, Y. Hisatsune, M. Tsunoda, M. Sahashi

Journal of Magnetics Society of Japan　39　(3)　107-110　2015/06

DOI： 10.3379/msjmag.1504R002 　
Perpendicular magnetic anisotropy of Mn4N films fabricated by reactive sputtering method Peer-reviewed

Kazuki Kabara, Masakiyo Tsunoda

JOURNAL OF APPLIED PHYSICS　117　(17)　17B512-1-17B512-4　2015/05

DOI： 10.1063/1.4913730 　

ISSN： 0021-8979

eISSN： 1089-7550
Mossbauer study on epitaxial CoxFe4-xN films grown by molecular beam epitaxy Peer-reviewed

Keita Ito, Tatsunori Sanai, Yoko Yasutomi, Toshiki Gushi, Kaoru Toko, Hideto Yanagihara, Masakiyo Tsunoda, Eiji Kita, Takashi Suemasu

JOURNAL OF APPLIED PHYSICS　117　(17)　17B717-1-17B717-4　2015/05

DOI： 10.1063/1.4914342 　

ISSN： 0021-8979

eISSN： 1089-7550
Fabrication of MgAl2O4 tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe4N ferromagnetic electrode Peer-reviewed

Masakiyo Tsunoda, Ryoichi Chiba, Kazuki Kabara

JOURNAL OF APPLIED PHYSICS　117　(17)　17D703-1-17D703-4　2015/05

DOI： 10.1063/1.4906762 　

ISSN： 0021-8979

eISSN： 1089-7550
16pCE-8 L-edge resonant magneto-optic effect of a Fe nanofilm by polarization-controlled soft X-ray source

Kubota Y., Taguchi M., Yamamoto Sh., Someya T., Tsuyama T., Ito S., Takubo K., Hirata Y., Yamamoto S., Miyawaki J., Araki M., Tsunoda M., Harada Y., Daimon H., Wadati H., Matsuda I.

Meeting Abstracts of the Physical Society of Japan　70　1174-1174　2015
Publisher: The Physical Society of Japan (JPS)
DOI： 10.11316/jpsgaiyo.70.2.0_1174 　

ISSN： 2189-079X
Anisotropic Magnetoresistance and Anomalous Hall Effects of pseudo single crystal Fe_4N thin films

TSUNODA Masakiyo, KABARA Kazuki, KOKADO Satoshi

ITE Technical Report　39　11-14　2015
Publisher: The Institute of Image Information and Television Engineers
DOI： 10.11485/itetr.39.37.0_11 　

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Fe_4N, a ferromagnetic inverse-perovskite-type transition-metal nitride with Curie temperature of 761 K, has attracted many attentions for its novel magneto-transport properties, originated from electron orbital hybridization between Fe and N atoms, and for its potential applications for spintronics as a highly spin-polarized material. In this talk, anomalous behaviors are reported for anisotropic magnetoresistance and anomalous Hall effects of pseudo single crystal Fe_4N thin films. We discuss the origin of these anomalous behaviors observed below 50 K through the analysis based on the electronic scattering theory.
Sign of the spin-polarization in cobalt-iron nitride films determined by the anisotropic magnetoresistance effect Peer-reviewed

Keita Ito, Kazuki Kabara, Tatsunori Sanai, Kaoru Toko, Yoji Imai, Masakiyo Tsunoda, Takashi Suemasu

JOURNAL OF APPLIED PHYSICS　116　(5)　053912-1-053912-7　2014/08

DOI： 10.1063/1.4892179 　

ISSN： 0021-8979

eISSN： 1089-7550
Dependence of Magnetic Damping on Temperature and Crystal Orientation in Epitaxial Fe4N Thin Films Peer-reviewed

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

Journal of Magnetics Society of Japan　38　(4)　162-168　2014/07
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1406R001 　

ISSN： 1882-2924

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In-plane and out-of-plane ferromagnetic resonance (FMR) were used to investigate the intrinsic magnetic damping constant (α) in epitaxial Fe₄N thin films deposited on MgO substrates. The dependence of α on temperature was evaluated from room temperature (RT) to 4 K. The external magnetic field (H) of FMR was applied in two directions, i.e., [100] and [110], of the Fe₄N lattice. Anisotropic α was observed from RT to 4 K. Moreover, the α for H // [100] exceeded the α for H // [110] at 180 K. Numerical calculations of α for bulk Fe₄N revealed the same behavior as that in the experiments. The temperature dependence of anisotropic α was explained by the changes in the electronic band structure depending on the directions of magnetization.
Annealing effects on nitrogen site ordering and anisotropic magnetoresistance in pseudo-single-crystal Y'-Fe4N films Peer-reviewed

Kazuki Kabara, Masakiyo Tsunoda, Satoshi Kokado

APPLIED PHYSICS EXPRESS　7　(6)　063003-1-063003-4　2014/06

DOI： 10.7567/APEX.7.063003 　

ISSN： 1882-0778

eISSN： 1882-0786
Observation of a giant Kerr rotation in a ferromagnetic transition metal by M-edge resonant magneto-optic Kerr effect Peer-reviewed

Sh. Yamamoto, M. Taguchi, M. Fujisawa, R. Hobara, S. Yamamoto, K. Yaji, T. Nakamura, K. Fujikawa, R. Yukawa, T. Togashi, M. Yabashi, M. Tsunoda, S. Shin, I. Matsuda

PHYSICAL REVIEW B　89　(6)　064423-1-064423-6　2014/02

DOI： 10.1103/PhysRevB.89.064423 　

ISSN： 1098-0121

eISSN： 1550-235X
Determination of Thermal Stability of Magnetic Tunnel Junction Using Time-Resolved Single-Shot Measurement Peer-reviewed

C. T. Chao, C. Y. Kuo, Lance Horng, M. Tsunoda, M. Takahashi, J. C. Wu

IEEE TRANSACTIONS ON MAGNETICS　50　(1)　1401204-1-1401204-4　2014/01

DOI： 10.1109/TMAG.2013.2276418 　

ISSN： 0018-9464

eISSN： 1941-0069
Anisotropic magnetoresistance effect of a strong ferromagnet: magnetization direction dependence in a model with crystal field Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 11, NO 5-6　11　(5-6)　1026-1032　2014

DOI： 10.1002/pssc.201300736 　

ISSN： 1862-6351
The Enhancement of Magnetic Damping in Fe4N Films with Increasing Thickness Peer-reviewed

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

JAPANESE JOURNAL OF APPLIED PHYSICS　52　(7)　073001-1-073001-3　2013/07

DOI： 10.7567/JJAP.52.073001 　

ISSN： 0021-4922
Enhancement of Spin Pumping Efficiency in Fe4N/Pt Bilayer Films Peer-reviewed

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

APPLIED PHYSICS EXPRESS　6　(6)　063004-1-063004-4　2013/06

DOI： 10.7567/APEX.6.063004 　

ISSN： 1882-0778
Studies on spintronics-related thin films using synchrotron-radiation-based Mossbauer spectroscopy Peer-reviewed

Ko Mibu, Makoto Seto, Takaya Mitsui, Yoshitaka Yoda, Ryo Masuda, Shinji Kitao, Yasuhiro Kobayashi, Edi Suharyadi, Masaaki Tanaka, Masakiyo Tsunoda, Hideto Yanagihara, Eiji Kita

HYPERFINE INTERACTIONS　217　(1-3)　127-135　2013/04

DOI： 10.1007/s10751-012-0734-0 　

ISSN： 0304-3843

eISSN： 1572-9540
Direction and Size of Ir Magnetic Moment Induced in MnIr/Co1-xFex Exchange Bias Bilayers from Resonant X-ray Magnetic Scattering Experiments at the Ir L-3 Absorption Edge Peer-reviewed

Nobuyoshi Hosoito, Kenji Kodama, Ryuichiro Yamagishi, Hirokazu Takahashi, Yohei Kota, Akimasa Sakuma, Masakiyo Tsunoda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　82　(3)　034711-1-034711-7　2013/03

DOI： 10.7566/JPSJ.82.034711 　

ISSN： 0031-9015
Anisotropic magnetoresistance effect: General expression of AMR ratio and intuitive explanation for sign of AMR ratio Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda

Advanced Materials Research　750-752　978-982　2013

DOI： 10.4028/www.scientific.net/AMR.750-752.978 　

ISSN： 1022-6680
Magnetotransport properties of dual MgO barrier magnetic tunnel junctions consisting of CoFeB/FeNiSiB/CoFeB free layers Peer-reviewed

D. K. Kim, J. U. Cho, B. S. Chun, K. H. Shin, K. J. Lee, M. Tsunoda, M. Takahashi, Y. K. Kim

APPLIED PHYSICS LETTERS　101　(23)　232401-1-232401-4　2012/12

DOI： 10.1063/1.4768931 　

ISSN： 0003-6951
Perpendicular Exchange Anisotropy in Mn-Ir/Fe-Co/[Pt/Co](4) Multilayers Peer-reviewed

Hirokazu Takahashi, Masakiyo Tsunoda, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　48　(11)　4347-4350　2012/11

DOI： 10.1109/TMAG.2012.2196760 　

ISSN： 0018-9464
Effect of Thermal Fluctuations of Magnetization on Perpendicular Exchange ANisotropy in Mn-Ir/[Co/Pt]n Multilayers Peer-reviewed

高橋宏和, 角田匡清, 高橋研

Journal of Magnetics Society of Japan　36　(5)　313-317　2012/09/01
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1207R001 　

ISSN： 1882-2924

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The dependence of perpendicular exchange anisotropy on the thickness of the ferromagnetic (FM) layer in Mn-Ir / [Co/Pt]_n multilayers was investigated. The dependencies on temperature of saturation magnetization, M_s, in [Co / Pt]_n multilayers having Co and Pt layers of various thicknesses were examined. The rate of decrease of M_s against temperature was large for thin-Co (< 1 nm) or thick-Pt layers ( > 1 nm), which indicates that thermal fluctuations in magnetization were significant. The unidirectional anisotropy constant, J_K, was reduced with the decreasing thickness of the interfacial Co layer in contact with the Mn-Ir layer. This suggested that perpendicular exchange bias was degraded by thermal fluctuations in FM magnetization during thermal annealing. The dependencies of J_K on the thicknesses of the Pt layer and inner Co layer could be also described by the thermal fluctuations in the magnetization of the FM layer.
An atomic model calculation of exchange anisotropy and uncompensated spin element in antiferromagnetic layer: An effect of exchange coupling with various ferromagnetic materials Peer-reviewed

C. Mitsumata, M. Tsunoda, H. Takahashi, A. Sakuma

EPL　99　(4)　47006-p1-47006-p4　2012/08

DOI： 10.1209/0295-5075/99/47006 　

ISSN： 0295-5075
Microscopic and Spectroscopic Studies of Light-Induced Magnetization Switching of GdFeCo Facilitated by Photoemission Electron Microscopy Peer-reviewed

Takuo Ohkochi, Hidenori Fujiwara, Masato Kotsugi, Arata Tsukamoto, Kuniaki Arai, Shinji Isogami, Akira Sekiyama, Jun'ichi Yamaguchi, Kazuaki Fukushima, Roman Adam, Claus M. Schneider, Tetsuya Nakamura, Kenji Kodama, Masakiyo Tsunoda, Toyohiko Kinoshita, Shigemasa Suga

JAPANESE JOURNAL OF APPLIED PHYSICS　51　(7)　073001-1-073001-5　2012/07

DOI： 10.1143/JJAP.51.073001 　

ISSN： 0021-4922

eISSN： 1347-4065
Disturbance-Free Observation of the Barkhausen Effet in Co/Pt Multilayer by X-ray Fourier Transform Holography Peer-reviewed

M. Suzuki, T. Nakamura, K. Nomura, S. Isogami, N. Awaji, M. Oura, E. Matsubara, T. Ishikawa, M. Tsunoda

Journal of Magnetics Society of Japan　36　(4)　304-307　2012/07

DOI： 10.3379/msjmag.1206R005 　
Negative Anisotropic Magnetoresistance in gamma '-Fe4N Epitaxial Films on SrTiO3(001) Grown by Molecular Beam Epitaxy Peer-reviewed

Keita Ito, Kazuki Kabara, Hirokazu Takahashi, Tatsunori Sanai, Kaoru Toko, Takashi Suemasu, Masakiyo Tsunoda

JAPANESE JOURNAL OF APPLIED PHYSICS　51　(6)　068001-1-068001-2　2012/06

DOI： 10.1143/JJAP.51.068001 　

ISSN： 0021-4922
Transport and switching behaviors in magnetic tunnel junctions consisting of CoFeB/FeNiSiB hybrid free layers Peer-reviewed

D. H. Kim, D. K. Kim, J. U. Cho, S. Y. Park, S. Isogami, M. Tsunoda, M. Takahashi, E. E. Fullerton, Y. K. Kim

JOURNAL OF APPLIED PHYSICS　111　(9)　093913-1-093913-4　2012/05

DOI： 10.1063/1.4709738 　

ISSN： 0021-8979

eISSN： 1089-7550
Current-induced switching of exchange bias in nano-scaled magnetic tunnel junctions with a synthetic antiferromagnetic pinned layer Peer-reviewed

C. T. Chao, C. Y. Kuo, Lance Horng, M. Tsunoda, M. Takahashi, J. C. Wu

JOURNAL OF APPLIED PHYSICS　111　(7)　07B103-1-07B103-3　2012/04

DOI： 10.1063/1.3673811 　

ISSN： 0021-8979

eISSN： 1089-7550
Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe4N, and Half-Metallic Ferromagnet: A Systematic Analysis Peer-reviewed

Satoshi Kokado, Masakiyo Tsunoda, Kikuo Harigaya, Akimasa Sakuma

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　81　(2)　024705-1-024705-17　2012/02

DOI： 10.1143/JPSJ.81.024705 　

ISSN： 0031-9015
Uncompensated antiferromagnetic moments in Mn-Ir/FM (FM =Ni-Co, Co-Fe, Fe-Ni) bilayers: Compositional dependence and its origin Peer-reviewed

Hirokazu Takahashi, Yohei Kota, Masakiyo Tsunoda, Tetsuya Nakamura, Kenji Kodama, Akimasa Sakuma, Migaku Takahashi

JOURNAL OF APPLIED PHYSICS　110　(12)　123920-1-123920-9　2011/12

DOI： 10.1063/1.3672450 　

ISSN： 0021-8979

eISSN： 1089-7550
Soft X-ray Magnetic Circular Dichroism of a CoFe/MnIr Exchange Bias Film under Pulsed High Magnetic Field Peer-reviewed

Tetsuya Nakamura, Yasuo Narumi, Toko Hirono, Misaki Hayashi, Kenji Kodama, Masakiyo Tsunoda, Shinji Isogami, Hirokazu Takahashi, Toyohiko Kinoshita, Koichi Kindo, Hiroyuki Nojiri

APPLIED PHYSICS EXPRESS　4　(6)　066602-1-066602-3　2011/06

DOI： 10.1143/APEX.4.066602 　

ISSN： 1882-0778
Current-in-plane Tunneling Measurement through Patterned Contacts on Top Surfaces of Magnetic Tunnel Junctions Invited Peer-reviewed

Ching-Ming Lee, Lin-Xiu Ye, Jia-Mou Lee, Yu-Cyun Lin, Chao-Yuan Huang, J. C. Wu, Masakiyo Tsunoda, Migaku Takahashi, Te-ho Wu

JOURNAL OF MAGNETICS　16　(2)　169-172　2011/06

DOI： 10.4283/JMAG.2011.16.2.169 　

ISSN： 1226-1750
Coupling strength with off-axial external field in magnetic tunnel junction cells Peer-reviewed

C. T. Chao, C. Y. Kuo, C. C. Chen, Lance Horng, Y. J. Chang, Te-Ho Wu, S. Isogami, M. Tsunoda, M. Takahashi, J. C. Wu

JOURNAL OF APPLIED PHYSICS　109　(7)　07B911-1-07B911-3　2011/04

DOI： 10.1063/1.3560047 　

ISSN： 0021-8979
Investigation on the Exchange Coupling Properties of Ring-Shaped MnIr/CoFe Bilayers Peer-reviewed

C. C. Chen, M. H. Shiao, Y. C. Lin, H. M. Tsai, C. Y. Kuo, Lance Horng, J. C. Wu, S. Isogami, M. Tsunoda, M. Takahashi

IEEE TRANSACTIONS ON MAGNETICS　47　(3)　620-623　2011/03

DOI： 10.1109/TMAG.2010.2100370 　

ISSN： 0018-9464
Development of Scanning-Type X-ray Fourier Transform Holography Peer-reviewed

K. Nomura, N. Awaji, S. Doi, S. Isogami, K. Kodama, T. Nakamura, M. Suzuki, M. Tsunoda

10TH INTERNATIONAL CONFERENCE ON X-RAY MICROSCOPY　1365　277-280　2011

DOI： 10.1063/1.3625358 　

ISSN： 0094-243X
Hard X-ray Fourier Transform Holography Using a Reference Scatterer Fabricated by Electron-Beam-Assisted Chemical-Vapor Deposition Peer-reviewed

M. Suzuki, Y. Kondo, S. Isogami, M. Tsunoda, S. Takahashi, S. Ishio

10TH INTERNATIONAL CONFERENCE ON X-RAY MICROSCOPY　1365　293-296　2011

DOI： 10.1063/1.3625362 　

ISSN： 0094-243X
X-ray Fourier transform holography using separated holography-mask Peer-reviewed

N. Awaji, K. Nomura, S. Doi, S. Isogami, M. Tsunoda, K. Kodama, M. Suzuki, T. Nakamura

Diamond Light Source Proceedings　1　({SRMS}-7)　2010/11
Publisher: Cambridge University Press ({CUP})
DOI： 10.1017/s204482011000047x 　

ISSN： 2044-8201
Influence of frequency and DC bias on magneto-impedance behaviors in double-MgO magnetic tunnel junctions Peer-reviewed

K. M. Kuo, C. Y. Lin, C. T. Lin, G. Chern, C. T. Chao, Lance Horng, J. C. Wu, Teho Wu, C. Y. Huang, H. Ohyama, S. Isogami, M. Tsunoda, M. Takahashi

SOLID STATE COMMUNICATIONS　150　(37-38)　1856-1859　2010/10

DOI： 10.1016/j.ssc.2010.06.008 　

ISSN： 0038-1098
Large Area Imaging by Fourier Transform Holography Using Soft and Hard X-rays Peer-reviewed

Naoki Awaji, Kenji Nomura, Shuuichi Doi, Shinji Isogami, Masakiyo Tsunoda, Kenji Kodama, Motohiro Suzuki, Tetsuya Nakamura

APPLIED PHYSICS EXPRESS　3　(8)　085201-1-085201-3　2010/08

DOI： 10.1143/APEX.3.085201 　

ISSN： 1882-0778
Linear correlation between uncompensated antiferromagnetic spins and exchange bias in Mn-Ir/Co100-xFex bilayers Peer-reviewed

Masakiyo Tsunoda, Hirokazu Takahashi, Tetsuya Nakamura, Chiharu Mitsumata, Shinji Isogami, Migaku Takahashi

APPLIED PHYSICS LETTERS　97　(7)　072501-1-072501-3　2010/08

DOI： 10.1063/1.3479500 　

ISSN： 0003-6951
Dependence of Magnetoresistance Effect in Fe4N/MgO/CoFeB-Magnetic Tunnel Junctions on Temperature Peer-reviewed

Y. Komasaki, M. Tsunoda, S. Isogami, C. C. Chen, M. Takahashi

Journal of Magnetics Society of Japan　34　(4)　524-528　2010/07
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1006R008 　

ISSN： 1882-2924

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We investigated the dependence of transport properties of Fe₄N/MgO/CoFeB-magnetic tunnel junctions (MTJs) on temperature. In antiparallel configurations of magnetizations of Fe₄N and CoFeB layers, a convex shaped peak was observed on the differential conductance curve as a function of bias voltage and it became clearer with decreasing temperature. The bias voltage (V_B) of ∼ -200 mV, where the peak was observed, corresponded to the energy where a sharp peak exists in the density of states (DOS) of the minority spin band of Fe₄N. The shape of the differential conductance curves suggested that the contribution of Δ₁ electron tunneling is not significant to total conductance in the Fe₄N/MgO/CoFeB-MTJs differently from that in CoFeB/MgO/CoFeB-MTJs, even though they have a similar crystallized MgO-barrier layer. The asymmetric shape of the dependence of the tunnel magnetoresistance (TMR) ratio on bias voltage did not change in a temperature range from 6 K to 300 K, but the absolute value of the maximum TMR ratio was monotonically increased from 76 % at 300 K to 103 % at 6K. Spin polarization of Fe₄N DOS at the Fermi level was estimated to be -0.5 from the present TMR ratio near zero bias and this was close to the theoretical value of -0.6.
Temperature Dependence of Electrical Transport and Magnetization Reversal in Magnetic Tunnel Junction Peer-reviewed

Chien-Tu Chao, Che-Chin Chen, Cheng-Yi Kuo, Cen-Shawn Wu, Lance Horng, Shinji Isogami, Masakiyo Tsunoda, Migaku Takahashi, Jong-Ching Wu

IEEE TRANSACTIONS ON MAGNETICS　46　(6)　2195-2197　2010/06

DOI： 10.1109/TMAG.2010.2045354 　

ISSN： 0018-9464
Correlation between Exchange Anisotropy and Crystal Structure of Ferromagnetic Layer in γ-Mn-Ir / Fe-Co-Ni Bilayers Peer-reviewed

H. Takahashi, M. Tsunoda, C. Mitsumata, M. Takahashi

Journal of Magnetics Society of Japan　34　(3)　285-288　2010/05
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1003R042 　

ISSN： 1882-2924

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The unidirectional anisotropy constant, J_K, of γ-Mn-Ir / FM (FM = Fe-Co-Ni) bilayers was investigated by systematically changing the composition of the Fe-Co-Ni layers. The FM layers were grown in the crystal structures corresponding to their composition on the (111)-oriented face centered cubic (fcc) Mn-Ir layer. J_K was significantly changed around the phase boundary of the FM layer between the body-centered cubic (bcc) phase and fcc-phase. The experimental results revealed a general feature where bcc-structured FM layers were more likely to induce stronger exchange anisotropy than fcc-structured FM layers. The J_K values and the lattice mismatch between the Mn-Ir layer and the FM layer were increased with increasing Co concentration in the bcc-FM region. The dependence of J_K on FM composition have been explained qualitatively with lattice distortion at the interface between the Mn-Ir and FM layers.
Time-resolved hard X-ray magnetic microprobe at SPring-8 Peer-reviewed

Motohiro Suzuki, Naomi Kawamura, Hitoshi Osawa, Masafumi Takagaki, Kanta Ono, Toshiaki Taniuchi, Shinji Isogami, Masakiyo Tsunoda

SRI 2009: THE 10TH INTERNATIONAL CONFERENCE ON SYNCHROTRON RADIATION INSTRUMENTATION　1234　129-+　2010

DOI： 10.1063/1.3463157 　

ISSN： 0094-243X
Inverse Current-Induced Magnetization Switching in Magnetic Tunnel Junctions with Fe4N Free Layer Peer-reviewed

Shinji Isogami, Masakiyo Tsunoda, Yosuke Komasaki, Akimasa Sakuma, Migaku Takahasi

APPLIED PHYSICS EXPRESS　3　(10)　103002-1-103002-3　2010

DOI： 10.1143/APEX.3.103002 　

ISSN： 1882-0778

eISSN： 1882-0786
Anomalous Anisotropic Magnetoresistance in Pseudo-Single-Crystal gamma '-Fe4N Films Peer-reviewed

Masakiyo Tsunoda, Hirokazu Takahashi, Satoshi Kokado, Yosuke Komasaki, Akimasa Sakuma, Migaku Takahashi

APPLIED PHYSICS EXPRESS　3　(11)　113003-1-113003-3　2010

DOI： 10.1143/APEX.3.113003 　

ISSN： 1882-0778
Influence of Diffused Boron Into MgO Barrier on Pinhole Creation in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions Peer-reviewed

Koujiro Komagaki, Masashi Hattori, Kenji Noma, Hitoshi Kanai, Kazuo Kobayashi, Yuji Uehara, Masakiyo Tsunoda, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　45　(10)　3453-3456　2009/10

DOI： 10.1109/TMAG.2009.2022189 　

ISSN： 0018-9464

eISSN： 1941-0069
Investigation on the Magnetization Reversal of Nanostructured Magnetic Tunnel Junction Rings Peer-reviewed

C. C. Chen, J. Y. Lin, Lance Horng, J. S. Yang, S. Isogami, M. Tsunoda, M. Takahashi, J. C. Wu

IEEE TRANSACTIONS ON MAGNETICS　45　(10)　3546-3549　2009/10

DOI： 10.1109/TMAG.2009.2023425 　

ISSN： 0018-9464
Antiferromagnet Thickness Dependence of the Training Effect in Exchange-Coupled CoFe/MnIr Bilayers Peer-reviewed

Dong Young Kim, Seok Soo Yoon, CheolGi Kim, M. Tsunoda, M. Takahashi

IEEE TRANSACTIONS ON MAGNETICS　45　(10)　3865-3868　2009/10

DOI： 10.1109/TMAG.2009.2022955 　

ISSN： 0018-9464

eISSN： 1941-0069
Systematic Study for Magnetization Dependence of Exchange Anisotropy Strength in Mn-Ir/FM (FM=Ni-Co, Co-Fe, Fe-Ni) Bilayer System Peer-reviewed

Masakiyo Tsunoda, Hirokazu Takahashi, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　45　(10)　3877-3880　2009/10

DOI： 10.1109/TMAG.2009.2024323 　

ISSN： 0018-9464
Negative Anisotropic Magnetoresistance in Fe4N Film Peer-reviewed

Masakiyo Tsunoda, Yosuke Komasaki, Satoshi Kokado, Shinji Isogami, Che-Chin Chen, Migaku Takahashi

APPLIED PHYSICS EXPRESS　2　(8)　083001-1-083001-3　2009/08

DOI： 10.1143/APEX.2.083001 　

ISSN： 1882-0778

eISSN： 1882-0786
Transport Properties of Magnetic Tunnel Junctions Comprising NiFeSiB/CoFeB Hybrid Free Layers Peer-reviewed

Ji Ung Cho, Do Kyun Kim, Reasmey P. Tan, Shinji Isogami, Masakiyo Tsunoda, Migaku Takahashi, Young Keun Kim

IEEE TRANSACTIONS ON MAGNETICS　45　(6)　2364-2366　2009/06

DOI： 10.1109/TMAG.2009.2018574 　

ISSN： 0018-9464

eISSN： 1941-0069
Effects of Field Cooling Direction on Magnetoresistance of Exchange-Biased Magnetic Tunnel Junction Rings Peer-reviewed

Che Chin Chen, Cheng Yi Kuo, Lance Horng, Shinji Isogami, Masakiyo Tsunoda, Migaku Takahashi, Jong Ching Wu

JAPANESE JOURNAL OF APPLIED PHYSICS　48　(5)　053001-1-053001-4　2009/05

DOI： 10.1143/JJAP.48.053001 　

ISSN： 0021-4922
75% inverse magnetoresistance at room temperature in Fe4N/MgO/CoFeB magnetic tunnel junctions fabricated on Cu underlayer Peer-reviewed

Yosuke Komasaki, Masakiyo Tsunoda, Shinji Isogami, Migaku Takahashi

JOURNAL OF APPLIED PHYSICS　105　(7)　07C928-1-07C928-3　2009/04

DOI： 10.1063/1.3072827 　

ISSN： 0021-8979
Current driven magnetization reversal in microstructured spin valve with current-in-plane configuration Peer-reviewed

C. Y. Kuo, C. T. Chao, J. Y. Ou, Lance Horng, J. C. Wu, Te-Ho Wu, M. Tsunoda, M. Takahashi

JOURNAL OF APPLIED PHYSICS　105　(7)　07D118-1-07D118-3　2009/04

DOI： 10.1063/1.3068483 　

ISSN： 0021-8979
Correlation between exchange bias field and domain size of ferromagnetic layer in Mn-Ir/Co-Fe bilayers Peer-reviewed

Hirokazu Takahashi, Masakiyo Tsunoda, Keiki Fukumoto, Tetsuya Nakamura, Kuniaki Arai, Toyohiko Kinoshita, Migaku Takahashi

JOURNAL OF APPLIED PHYSICS　105　(7)　07D720-1-07D720-3　2009/04

DOI： 10.1063/1.3073659 　

ISSN： 0021-8979

eISSN： 1089-7550
Tailor-made nano-structured materials for perpendicular recording media and head-precise control of direct/indirect exchange coupling Invited Peer-reviewed

Migaku Takahashi, Masakiyo Tsunoda, Shin Saito

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　321　(6)　539-544　2009/03

DOI： 10.1016/j.jmmm.2008.05.008 　

ISSN： 0304-8853

eISSN： 1873-4766
XFELによる極小デバイス磁化挙動解析のための回折スペックル計測技術の開発

角田匡清, 中村哲也, 鈴木基寛, 淡路直樹

日本結晶学会誌　51　s14　2009
Publisher: The Crystallographic Society of Japan
DOI： 10.5940/jcrsj.51.s14 　

ISSN： 0369-4585
27pPSA-44 Development of soft x-ray MCD measurement technique using pulsed high magnetic field Peer-reviewed

Nakamura Tetsuya, Narumi Yasuo, Hirono Toko, Kodama Kenji, Hayashi Misaki, Tsunoda Masakiyo, Kindo Koichi, Nojiri Hiroyuki, Kinoshita Toyohiko

Meeting Abstracts of the Physical Society of Japan　64　(0)　391-391　2009
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.64.2.3.0_391_2 　

ISSN： 1342-8349
Spin Polarization of Sub-monolayer Cu Embedded in Fe70Co30 Films Peer-reviewed

S. Isogami, M. Tsunoda, T. Nakamura, M. Takahashi

Journal of Magnetics Society of Japan　32　(6)　540-542　2008/11
Publisher: The Magnetics Society of Japan (MSJ)
DOI： 10.3379/msjmag.32.540 　

ISSN： 1882-2924

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Spin polarization of Cu embedded in Fe₇₀Co₃₀ films has been investigated by means of transmission x-ray magnetic circular dichroism (XMCD). [Fe₇₀Co₃₀(d_FeCo) / Cu(d_Cu)]_n multilayered films were fabricated on Si-N membrane substrate, fixing total thickness of Fe-Co and Cu layers. Magneto-optical sum-rules were applied to the measured absorption and XMCD spectra to determine quantitatively the spin and orbital moments of Cu. With decreasing the Cu layer thickness, the spin moment of Cu increases but exhibits to be saturated about 0.1 μ_B / atom. The small value of spin moment (0.1 μ_B), comparing to that of the 3d transition metals such as Fe and Co, implies that only the top part of 3d down-spin band of Cu is unoccupied in these specimens.
In situ heat treatment of ultrathin MgO layer for giant magnetoresistance ratio with low resistance area product in CoFeB/MgO/CoFeB magnetic tunnel junctions Peer-reviewed

Shinji Isogami, Masakiyo Tsunoda, Kojiro Komagaki, Kazuyuki Sunaga, Yuji Uehara, Masashige Sato, Toyoo Miyajima, Migaku Takahashi

APPLIED PHYSICS LETTERS　93　(19)　192109-1-192109-3　2008/11

DOI： 10.1063/1.3021372 　

ISSN： 0003-6951

eISSN： 1077-3118
Magnetoresistance Variation of Magnetic Tunnel Junctions with NiFeSiB/CoFeB Free Layers Depending on MgO Tunnel Barrier Thickness Peer-reviewed

Ji Ung Cho, Do Kyun Kim, Tian Xing Wang, Shinji Isogami, Masakiyo Tsunoda, Migaku Takahashi, Young Keun Kim

IEEE TRANSACTIONS ON MAGNETICS　44　(11)　2547-2550　2008/11

DOI： 10.1109/TMAG.2008.2003244 　

ISSN： 0018-9464

eISSN： 1941-0069
Enhanced Exchange Anisotropy by Ultra-Thin Cox Fe100-x(x > 80) Layer Insertion at the Interface of L1(2)-Ordered Mn3Ir/Co65Fe35 Bilayers Peer-reviewed

K. Komagaki, M. Tsunoda, H. Takahashi, K. Noma, H. Kanai, K. Kobayashi, Y. Uehara, M. Takahashi

IEEE TRANSACTIONS ON MAGNETICS　44　(11)　2832-2834　2008/11

DOI： 10.1109/TMAG.2008.2001334 　

ISSN： 0018-9464
Tunnel magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeB/MgO/CoFeB pseudo-spin-valves annealed at high temperature Peer-reviewed

S. Ikeda, J. Hayakawa, Y. Ashizawa, Y. M. Lee, K. Miura, H. Hasegawa, M. Tsunoda, F. Matsukura, H. Ohno

APPLIED PHYSICS LETTERS　93　(8)　082508-1-082508-3　2008/08

DOI： 10.1063/1.2976435 　

ISSN： 0003-6951

eISSN： 1077-3118
Compositional Dependence of Exchange Anisotropy in g-Mn-Ir-Rh-Ru / Co70Fe30 Bilayers Peer-reviewed

M. Tsunoda, T. Kato, Y. Ashizawa, Y. Suzuki, M. Takahashi

Journal of the Magnetics Society of Japan　32　(4)　445-446　2008/07
Publisher: The Magnetics Society of Japan (MSJ)
DOI： 10.3379/msjmag.32.445 　

ISSN： 1882-2924

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Exchange anisotropy of quaternary γ-Mn-Ir-Rh-Ru / Co₇₀Fe₃₀ bilayer has been investigated. Unidirectional anisotropy constant, J_K, exhibited gradual change against the chemical composition of the quaternary system. Contour map of J_K shows a broad peak at the compositional range from Mn₇₅Ir₂₅ to Mn₇₉Ir₁₅Rh₆. The J_K decreases mainly along the direction to which the Ru content increases. The thinnest critical thickness of the antiferromagnetic layer is obtained for Mn-Ir alloy among the respective terminal binary alloy systems. We concluded that Mn-Ir is the most promising antiferromagnetic material for exchange-biased bilayers in ultra-high density hard disk drives among the present γ-Mn-Ir-Rh-Ru quaternary system.
Critical thickness of antiferromagnetic layer in exchange biasing bilayer system Peer-reviewed

Chiharu Mitsumata, Akimasa Sakuma, Kazuaki Fukamichi, Masakiyo Tsunoda, Migaku Takahashi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　77　(4)　044602-1-044602-6　2008/04

DOI： 10.1143/JPSJ.77.044602 　

ISSN： 0031-9015
Correlation between spin dependent scattering and impurity polarization in CPP-GMR spin valves with ultra thin Cu inserted Fe-Co layers Peer-reviewed

S. Isogami, M. Tsunoda, K. Noguchi, T. Nakamura, H. Osawa, M. Takahashi

Physica Status Solidi (A) Applications and Materials Science　204　(12)　4033-4036　2007/12

DOI： 10.1002/pssa.200777306 　

ISSN： 1862-6300 1862-6319
Correlation between spin dependent scattering and impurity polarization in CPP-GMR spin valves with ultra thin Cu inserted Fe-Co layers Peer-reviewed

S. Isogami, M. Tsunoda, K. Noguchi, T. Nakamura, H. Osawa, M. Takahashi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE　204　(12)　4033-4036　2007/12

DOI： 10.1002/pssa.200777306 　

ISSN： 0031-8965
Enhancement of exchange bias by ultra-thin Mn layer insertion at the interface of Mn-Ir/Co-Fe bilayers Peer-reviewed

M. Tsunoda, S. Yoshitaki, Y. Ashizawa, D. Y. Kim, C. Mitsumata, M. Takahashi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS　244　(12)　4470-4473　2007/12

DOI： 10.1002/pssb.200777391 　

ISSN： 0370-1972
Large exchange bias and high blocking temperature of MgO-Barrier-MTjs with L1(2)-Ordered Mn(3)lr Peer-reviewed

Koujiro Komagaki, Kouji Yamada, Kenji Noma, Hitoshi Kanai, Kazuo Kobayashi, Yuji Uehara, Masakiyo Tsunoda, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　43　(8)　3535-3537　2007/08

DOI： 10.1109/TMAG.2007.893695 　

ISSN： 0018-9464
CoFeB/MgO/CoFeB強磁性トンネル接合におけるMgO障壁層の結晶配向制御および巨大トンネル磁気抵抗効果の導出 Peer-reviewed

Y. Ashizawa, H. Ohyama, K. Sunaga, Y. Watanabe, M. Tsunoda, M. Takahashi

Giant Magnetoresistance Effect Derived by Controlling Crystallographic Orientation of MgO Barrier in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions　31　(5)　411-415　2007/08
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.31.411 　

ISSN： 0285-0192

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Crystallographic orientation of the MgO barrier in sputter-deposited CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) and its effect on tunnel magnetoresistance (TMR) were investigated. The degree of MgO(001) orientation was estimated with the integral intensity ratio (I₍₂₀₀₎ /I₍₂₂₀₎) of diffraction lines from MgO(200) and MgO(220) planes obtained in grazing incident x-ray diffraction profiles. The main results are stated as follows. (1) I₍₂₀₀₎ /I₍₂₂₀₎ ∼ 4, meaning the (001) orientation of MgO, is realized when the underlaid CoFeB maintains amorphous structure, meanwhile MgO on bcc(110)-oriented CoFe shows (111) orientation (I₍₂₀₀₎ /I₍₂₂₀₎ = 0). (2) The prevention of epitaxial growth on hcp(00.1)-oriented Ru layer is effective to maintain amorphous structure of CoFeB. (3) The achievable TMR ratio after high temperature (280 °C − 450 °C) annealing is mainly dominated by the MgO orientation and giant TMR ratio exceeding 200% is only obtained with I₍₂₀₀₎ /I₍₂₂₀₎ ≥ 3.4, while the resistance area product is independent of I₍₂₀₀₎ /I₍₂₂₀₎. (4) Thin Mg layer inserted between CoFeB layer and MgO barrier is effective to obtain bcc(001)-oriented crystallization of CoFeB after high temperature annealing and results in a giant TMR ratio, because of its role to avoid surface oxidization of underlying ferromagnetic electrode during the deposition of MgO barrier.
Inverse tunnel magnetoresistance in magnetic tunnel junctions with an Fe4N electrode Peer-reviewed

Kazuyuki Sunaga, Masakiyo Tsunoda, Kojiro Komagaki, Yuji Uehara, Migaku Takahashi

JOURNAL OF APPLIED PHYSICS　102　(1)　013917-1-013917-4　2007/07

DOI： 10.1063/1.2753576 　

ISSN： 0021-8979
Controllable remanent states on microstructured magnetic tunnel junction rings Peer-reviewed

C. C. Chen, C. T. Chao, C. Y. Kuo, Lance Horng, Teho Wu, G. Chern, C. Y. Huang, S. Isogami, M. Tsunoda, M. Takahashi, J. C. Wu

IEEE TRANSACTIONS ON MAGNETICS　43　(6)　2824-2826　2007/06

DOI： 10.1109/TMAG.2007.894206 　

ISSN： 0018-9464
Oxidation process of Mg films by using high-concentration ozone for magnetic tunnel junctions Peer-reviewed

Satoru Yoshimura, Yosuke Narisawa, Yoshihiko Watanabe, Masakiyo Tsunoda, Migaku Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　312　(1)　176-180　2007/05

DOI： 10.1016/j.jmmm.2006.09.025 　

ISSN： 0304-8853

eISSN： 1873-4766
Uncompensated antiferromagnetic spins at the interface in Mn-Ir based exchange biased bilayers Peer-reviewed

M. Tsunoda, S. Yoshitaki, Y. Ashizawa, C. Mitsumata, T. Nakamura, H. Osawa, T. Hirono, D. Y. Kim, M. Takahashi

JOURNAL OF APPLIED PHYSICS　101　(9)　09E510-1-09E510-3　2007/05

DOI： 10.1063/1.2710216 　

ISSN： 0021-8979
Magnetic viscosity phenomena in exchange coupled CoFe/MnIr bilayers Peer-reviewed

Dong Young Kim, C. O. Kim, M. Tsunoda, M. Yamaguchi, S. Yabugami, M. Takahashi

JOURNAL OF APPLIED PHYSICS　101　(9)　09E511-1-09E511-3　2007/05

DOI： 10.1063/1.2710219 　

ISSN： 0021-8979
Size dependence of magnetization reversal of ring shaped magnetic tunnel junction Peer-reviewed

C. C. Chen, C. Y. Kuo, Y. C. Chang, C. C. Chang, Lance Horng, Teho Wu, G. Chern, Y. Huang, M. Tsunoda, M. Takahashi, J. C. Wu

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　310　(2)　1900-1902　2007/03

DOI： 10.1016/j.jmmm.2006.10.686 　

ISSN： 0304-8853
Formation of CCP-NOL in CPP-GMR spin valve structure for the enhancement of magnetoresistance Peer-reviewed

Y. M. Kang, S. Isogami, M. Tsunoda, M. Takahashi, S. I. Yoo

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　310　(2)　1911-1913　2007/03

DOI： 10.1016/j.jmmm.2006.10.922 　

ISSN： 0304-8853
Angular dependence of magnetoresistance during magnetization reversal on magnetic tunnel junction ring Peer-reviewed

C. C. Chen, C. C. Chang, Y. C. Chang, C. T. Chao, C. Y. Kuo, Lance Horng, J. C. Wu, Teho Wu, G. Chern, C. Y. Huang, M. Tsunoda, M. Takahashi

IEEE TRANSACTIONS ON MAGNETICS　43　(2)　920-922　2007/02

DOI： 10.1109/TMAG.2006.888511 　

ISSN： 0018-9464
Sputtering Target for Information Network Devices —Present and Future— Peer-reviewed

Migaku Takahashi, Shin Saito, Masakiyo Tsunoda

Shinku/Journal of the Vacuum Society of Japan　50　(1)　22-27　2007

DOI： 10.3131/jvsj.50.22 　

ISSN： 0559-8516
Annealing temperature dependence of microwave permeability in CoFe/MnIr bilayers Peer-reviewed

Dong Young Kim, B. Parvatheeswara Rao, Chong-Oh Kim, Masakiyo Tsunoda, Migaku Takahashi

PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 12　4　(12)　4388-+　2007

DOI： 10.1002/pssc.200777412 　

ISSN： 1862-6351
Soft x-ray magnetic circular dichroism study of Mn-Ir/Co-Fe bilayers with giant exchange anisotropy Peer-reviewed

M. Tsunoda, T. Nakamura, M. Naka, S. Yoshitaki, C. Mitsumata, M. Takahashi

APPLIED PHYSICS LETTERS　89　(17)　172501-1-172501-3　2006/10

DOI： 10.1063/1.2364116 　

ISSN： 0003-6951
Current-induced magnetization switching and CPP-GMR in 30 nm phi scale spin valves fabricated using EB-assisted CVD hard masks Peer-reviewed

Shinji Isogami, Masakiyo Tsunoda, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　42　(10)　2676-2678　2006/10

DOI： 10.1109/TMAG.2006.878858 　

ISSN： 0018-9464
Exchange anisotropy of L1(2)-Mn3X (X = Ir, Rh, Ru)/Co-Fe bilayers Peer-reviewed

Masakiyo Tsunoda, Mamiko Naka, Ken-Ichi Imakita, Shin-Ichiro Yoshitaki, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　42　(10)　2999-3001　2006/10

DOI： 10.1109/TMAG.2006.879153 　

ISSN： 0018-9464
Critical angle-behavior of exchange bias and coercivity in CoFe/MnIr bilayers Peer-reviewed

Dong Young Kim, CheolGi Kim, Chong-Oh Kim, M. Naka, M. Tsunoda, M. Takahashi

IEEE TRANSACTIONS ON MAGNETICS　42　(10)　3011-3013　2006/10

DOI： 10.1109/TMAG.2006.879756 　

ISSN： 0018-9464
Effect of axial ratio and atomic volume on magnetism of alpha ' and gamma '-Fe-N Peer-reviewed

Kazuyuki Sunaga, Masakiyo Tsunoda, Migaku Takahashi

IEEE TRANSACTIONS ON MAGNETICS　42　(10)　3020-3022　2006/10

DOI： 10.1109/TMAG.2006.878427 　

ISSN： 0018-9464
L1(2) phase formation and giant exchange anisotropy in Mn3Ir/Co-Fe bilayers Invited Peer-reviewed

M Tsunoda, K Imakita, M Naka, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　55-59　2006/09

DOI： 10.1016/j.jmmm.2006.02.007 　

ISSN： 0304-8853
Angular dependence of exchange bias and coercivity in polycrystalline CoFe/MnIr bilayers Peer-reviewed

Dong Young Kim, CheolGi Kim, Chong-Oh Kim, M. Tsunoda, M. Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E56-E58　2006/09

DOI： 10.1016/j.jmmm.2006.01.220 　

ISSN： 0304-8853
Tunable magnetic anisotropy of antiferromagnetic superlattice and resultant exchange bias of ferromagnetic layer on it Peer-reviewed

Masakiyo Tsunoda, Mamiko Naka, Dong Young Kim, Migaku Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E88-E90　2006/09

DOI： 10.1016/j.jmmm.2006.01.187 　

ISSN： 0304-8853
Magnetization switching of NiFeSiB free layers for magnetic tunnel junctions Peer-reviewed

B. S. Chun, S. P. Ko, B. S. Oh, J. Y. Hwang, J. R. Rhee, T. W. Kim, S. Saito, S. Yoshimura, M. Tsunoda, M. Takahashi, Y. K. Kim

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E258-E260　2006/09

DOI： 10.1016/j.jmmm.2006.02.052 　

ISSN： 0304-8853
Effect of surface roughness and field annealing on interlayer coupling in MnIr-based magnetic tunnel junction Peer-reviewed

Dong Young Kim, Cheol Gi Kim, Chong-Oh Kim, M. Tsunoda, M. Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E267-E269　2006/09

DOI： 10.1016/j.jmmm.2006.01.128 　

ISSN： 0304-8853
The switching characteristics of free layer of patterned magnetic tunnel junction device Peer-reviewed

C. C. Chen, Y. R. Wang, C. Y. Kuo, J. C. Wu, Lance Horng, Teho Wu, S. Yoshimura, M. Tsunoda, M. Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E285-E287　2006/09

DOI： 10.1016/j.jmmm.2006.02.020 　

ISSN： 0304-8853
Negative coercivity characteristics in antiferromagnetic coupled hard/soft multilayers Peer-reviewed

DongYoung Kim, CheolGi Kim, Chong-Oh Kim, Seok Soo Yoon, Mamiko Naka, Masakiyo Tsunoda, Migaku Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　304　(1)　E356-E358　2006/09

DOI： 10.1016/j.jmmm.2006.01.198 　

ISSN： 0304-8853
Magnetization switching of CoFeSiB free-layered magnetic tunnel junctions Peer-reviewed

Byong Sun Chun, Jae Youn Hwang, Jang Roh Rhee, Taewan Kim, Shin Saito, Satoru Yoshimura, Masakiyo Tsunoda, Migaku Takahashi, Young Keun Kim

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　303　(2)　E223-E225　2006/08

DOI： 10.1016/j.jmmm.2006.01.041 　

ISSN： 0304-8853
XMCD study of Mn-Ir/Co-Fe bilayers with giant exchange anisotropy Peer-reviewed

M. Tsunoda, T. Nakamura, M. Naka, S. Yoshitaki, C. Mitsumata, M. Takahashi

INTERMAG 2006 - IEEE International Magnetics Conference　410　2006

DOI： 10.1109/INTMAG.2006.376134 　
Current induced magnetization switching in 30nm√è? scale CPP-GMR spin valves fabricated using EB assisted CVD hard masks Peer-reviewed

S. Isogami, M. Tsunoda, M. Takahashi

INTERMAG 2006 - IEEE International Magnetics Conference　709　2006

DOI： 10.1109/INTMAG.2006.376433 　
Structure and magnetism of c-plane-oriented Mn50(Te 50-xSbx) pseudo-single crystal films Peer-reviewed

Y. Ashizawa, S. Saito, M. Tsunoda, M. Takahashi

INTERMAG 2006 - IEEE International Magnetics Conference　174　2006

DOI： 10.1109/INTMAG.2006.375674 　
Synthesis and magnetic moment of bct and fct-Fe-N Peer-reviewed

K. Sunaga, M. Tsunoda, M. Takahashi

INTERMAG 2006 - IEEE International Magnetics Conference　872　2006

DOI： 10.1109/INTMAG.2006.374903 　
Uncompensated spin elements in ferromagnetic and antiferromagnetic bilayer with non-collinear spin structure Invited Peer-reviewed

Chiharu Mitsumata, Akimasa Sakuma, Kazuaki Fukamichi, Masakiyo Tsunoda

Materials Transactions　47　(1)　11-14　2006/01

DOI： 10.2320/matertrans.47.11 　

ISSN： 1345-9678
Angular dependence of exchange bias and coercive field in CoFe/MnIr epitaxial bilayers Peer-reviewed

DY Kim, CG Kim, CO Kim, M Shibata, M Tsunoda, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　2712-2714　2005/10

DOI： 10.1109/TMAG.2005.854762 　

ISSN： 0018-9464
Intergranular tunneling magnetoresistance of mechanically alloyed (Cr-,M)O-2 powder compacts Peer-reviewed

M Tsunoda, T Sato, Q Zhang, B Jeyadevan, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　3400-3402　2005/10

DOI： 10.1109/TMAG.2005.855213 　

ISSN： 0018-9464
30-nm scale fabrication of magnetic tunnel junctions using EB assisted CVD hard masks Peer-reviewed

S Isogami, M Tsunoda, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　3607-3609　2005/10

DOI： 10.1109/TMAG.2005.854786 　

ISSN： 0018-9464
High-Concentration Ozone Oxidation Process of a Metal Al Film and Tunnel Magnetoresistance Properties of Magnetic Tunnel Junctions with Ozone-Oxidized Al-O Barriers Peer-reviewed

S. Yoshimura, Y. Narisawa, M. Tsunoda, M. Takahashi

Journal of Magnetic Society of Japan　29　(8)　820-825　2005/08/01
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.29.820 　

ISSN： 0285-0192

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The ozone oxidization process of metal Al film for the formation of barriers in magnetic tunnel junctions (MTJs) is investigated. The ozone exposure method, in which atomic oxygen in the ground state is an oxidizing species, is expected to oxidize ultra-thin Al films more mildly than the plasma oxidization method, since the energy level of atomic oxygen is ∼2 eV lower in the ozone method than in the plasma method. The main results were as follows: (1) In the case of ozone oxidation, the diffusion coefficient of oxygen in Al-O is much smaller than in the plasma oxidation case. (2) Ozone oxidation of Al films is spontaneously stopped at the interface to the bottom Co-Fe, regardless of the exposure amount. (3) In the case of plasma oxidation, the exposure condition in which the TMR ratio reaches its maximum shifts with increasing Al layer thickness. However, in the case of ozone oxidation, that exposure condition does not shift, regardless of the Al layer thickness. (4) In MTJs fabricated by ozone oxidation, a high TMR ratio is obtained without annealing. We conclude from all these findings that ozone oxidation of metal Al layers is a promising barrier formation process for realizing high-quality and very thin insulating layers.
Synthesis and Magnetic Moment of α' and γ'-Fe-N Phases with Various N Contents Peer-reviewed

K. Sunaga, M. Tsunoda, M. Takahashi

Journal of Magnetic Society of Japan　29　(5)　553-557　2005/05
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.29.553 　

ISSN： 0285-0192

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α' and γ'-Fe-N with various N contents were synthesized by using multilayer fabrication technique and the volume effect on magnetic moment for these phases was examined. The unit-cell volume of α' and γ' phases monotonously increases with increasing N content. In the case of α'-Fe-N, magnetic moment decreases with increasing unit-cell volume. This result is different from theoretical prediction. On the other hand, in the case of γ'-Fe-N, magnetic moment takes the maximum near the volume of bulk γ'-Fe₄N. In particular, the magnetic moment drops drastically near the volume of bulk γ'-Fe₄N, although unit-cell volume is almost same. This result is also different from the theory. Further experimental works including magnetic microstructural analysis are needed to answer these discrepancies.
Effect of ion bombardment to Al-N barrier in Magnetic Tunnel Junctions on their TMR properties Peer-reviewed

M. Tsunoda, Y. Watanabe, K. Umakita, S. Yoshimura, M. Takahashi

Journal of Magnetic Society of Japan　29　(6)　653-657　2005/05
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.29.653 　

ISSN： 0285-0192

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Effect of in-situ ion bombardment to Al-N barrier in magnetic tunnel junctions (MTJ) on their tunnel magnetoresistance (TMR) was investigated in correlation with the local conducting properties of Al-N barrier. Slight ion bombardment increased the barrier height of Al-N from 1.2eV to 1.8∼1.9eV, and resulted in the enhancement of TMR ratio from 34% to 37% in as-made MTJ. On the other hand, strong ion bombardment, longer bombardment duration than 10s, produced high conductive channels (pinholes) in the Al-N barrier, and deteriorated the TMR ratio down to 20% and more. Simple calculation for TMR ratio and resistance-area product of MTJs with using the pinhole density and the local conducting properties, determined from conducting-AFM measurement, well explained the experimental features.
Thickness dependence of exchange anisotropy of polycrystalline Mn3Ir/Co-Fe bilayers Peer-reviewed

K Imakita, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　97　(10)　10K106-1-10K106-3　2005/05

DOI： 10.1063/1.1850858 　

ISSN： 0021-8979
Surface flattening processes of metal layer and their effect on transport properties of magnetic tunnel junctions with Al-N barrier Peer-reviewed

S Yoshimura, T Nozawa, T Shoyama, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　97　(10)　10C920-1-10C920-3　2005/05

DOI： 10.1063/1.1854452 　

ISSN： 0021-8979
Radical nitridation of Al films for the barrier formation in ferromagnetic tunnel junctions Peer-reviewed

M Tsunoda, T Shoyama, S Yoshimura, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　286　162-166　2005/02

DOI： 10.1016/j.jmmm.2004.10.098 　

ISSN： 0304-8853
Magnetization reversal of ferromagnetic layer in exchange coupled Mn-Ir/Co-Fe epitaxial bilayers Peer-reviewed

T Sato, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　286　206-210　2005/02

DOI： 10.1016/j.jmmm.2004.09.052 　

ISSN： 0304-8853
Improved thermal stability of exchange bias of Mn-Ir/Co-Fe bilayers by novel in situ thermal annealing procedure Peer-reviewed

KI Imakita, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　286　248-252　2005/02

DOI： 10.1016/j.jmmm.2004.09.073 　

ISSN： 0304-8853
30 nm-scale-fabrication of magnetic tunnel junctions using electron beam assisted CVD hard masks

S. Isogami, M. Tsunoda, M. Takahashi

INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference　765　2005
Publisher: IEEE Computer Society
DOI： 10.1109/intmag.2005.1464196 　
Local transport properties of Co-Fe/Al-O/Co-Fe tunnel junctions with high thermal stability Peer-reviewed

TS Yoon, T Shoyama, YW Lee, M Tsunoda, M Takahashi, DY Kim, CO Kim

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　284　330-335　2004/12

DOI： 10.1016/j.jmmm.2004.07.032 　

ISSN： 0304-8853
Relation between exchange coupling and enhanced coercivity in the free layer of a patterned magnetic tunnel junction Peer-reviewed

CG Kim, CO Kim, M Tsunoda, M Takahashi, T Stobiecki

JOURNAL OF APPLIED PHYSICS　96　(12)　7399-7402　2004/12

DOI： 10.1063/1.1811776 　

ISSN： 0021-8979
Giant exchange anisotropy observed in Mn-Ir/Co-Fe bilayers containing ordered Mn3Ir phase Peer-reviewed

K Imakita, M Tsunoda, M Takahashi

APPLIED PHYSICS LETTERS　85　(17)　3812-3814　2004/10

DOI： 10.1063/1.1812597 　

ISSN： 0003-6951
Magnetotransport properties of Co-Fe/Al-N/Co-Fe tunnel junctions with large tunnel magnetoresistance ratio Peer-reviewed

TS Yoon, CO Kim, T Shoyama, M Tsunoda, M Takahashi

APPLIED PHYSICS LETTERS　85　(1)　82-84　2004/07

DOI： 10.1063/1.1765203 　

ISSN： 0003-6951
Nitridation process of Al layer by microwave-excited plasma and large magnetoresistance in Co-Fe/Al-N/Co-Fe tunnel junctions - As a comparison with oxidization process Peer-reviewed

S Yoshimura, T Shoyama, T Nozawa, M Tsunoda, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　40　(4)　2290-2292　2004/07

DOI： 10.1109/TMAG.2004.829824 　

ISSN： 0018-9464
Orientational dependence of exchange anisotropy of Mn-Ir/Co-Fe epitaxial bilayers Peer-reviewed

Takashi Sato, Masakiyo Tsunoda, Migaku Takahashi

Journal of Applied Physics　95　(11)　7513-7515　2004/06/01

DOI： 10.1063/1.1669116 　

ISSN： 0021-8979
Correlation between structure and exchange coupling parameters of IrMn based MTJ Peer-reviewed

T Stobiecki, J Kanak, J Wrona, M Czapkiewicz, CG Kim, CO Kim, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH　201　(8)　1621-1627　2004/06

DOI： 10.1002/pssa.200304661 　

ISSN： 0031-8965
Temperature dependence of tunnel magnetoresistance and magnetization of IrMn based MTJ Peer-reviewed

P Wisniowski, T Stobiecki, M Czapkiewicz, J Wrona, M Rams, CG Kim, CO Kim, YK Hu, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH　201　(8)　1648-1652　2004/06

DOI： 10.1002/pssa.200304595 　

ISSN： 0031-8965
Exchange anisotropy of polycrystalline Mn-Ir/Co-Fe bilayers enlarged by long-time annealing Peer-reviewed

M Tsunoda, T Sato, T Hashimoto, M Takahashi

APPLIED PHYSICS LETTERS　84　(25)　5222-5224　2004/06

DOI： 10.1063/1.1765739 　

ISSN： 0003-6951
Distribution of interlayer-exchange coupling on MTJ multilayer Peer-reviewed

CG Kim, VK Sankaranarayanan, CO Kim, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE　201　(8)　1635-1639　2004/06

DOI： 10.1002/pssa.200304596 　

ISSN： 1862-6300
Magnetization process and domains in MTJ Peer-reviewed

M Czapkiewicz, M Zoladz, J Wrona, P Wisniowski, R Rak, T Stobiecki, CG Kim, CO Kim, M Takahashi, M Tsunoda

PHYSICA STATUS SOLIDI B-BASIC RESEARCH　241　(7)　1477-1481　2004/06

DOI： 10.1002/pssb.200304668 　

ISSN： 0370-1972
Formability and thermal stability of alpha' phase in (Fe1-y Co-y)-(B, C, N) films Peer-reviewed

K Sunaga, S Kadowaki, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI B-BASIC RESEARCH　241　(7)　1701-1705　2004/06

DOI： 10.1002/pssb.200304622 　

ISSN： 0370-1972
Correlation among exchange coupling, surface roughness and junction size in magnetic tunnel junctions Peer-reviewed

VK Sankaranarayanan, YK Hu, C Kim, CO Kim, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　272　1965-1966　2004/05

DOI： 10.1016/j.jmmm.2004.01.019 　

ISSN： 0304-8853
The influence of NiFe thickness of top-electrode on exchange coupling parameters of IrMn based MTJ Peer-reviewed

T. Stobiecki, C. G. Kim, C. O. Kim, Y. K. Hu, M. Czapkiewicz, J. Kanak, J. Wrona, M. Tsunoda, M. Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　272　E1503-E1505　2004/05

DOI： 10.1016/j.jmmm.2003.12.311 　

ISSN： 0304-8853
Lateral Grain Size Enlargement and Surface Flattening of Cu Thin Films by using Adequate Underlayers and by Thermal Annealing in Ultra High Vacuum Peer-reviewed

Kenichi Imakita, Masakiyo Tsunoda, Migaku Takahashi

Journal of the Vaccum Society of Japan　47　(3)　124-127　2004/04
Publisher: The Vacuum Society of Japan
DOI： 10.3131/jvsj.47.124 　

ISSN： 0559-8516

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The effects of body centered cubic (BCC) solid solution underlayers on the metallurgical size and flatness of Cu thin films, fabricated on them, were investigated. As the underlayer materials, Cr₈₀Al₂₀, Cr₉₀Ni₁₀, Cr₈₀Fe₂₀, Fe₇₅Cr₂₅ and Fe were examined. Lateral grain size of the Cu films fabricated on the Cr-Al, Cr-Ni, Cr-Fe, Fe-Cr under layer was enlarged, comparing to that on the Fe underlayer. The difference between the surface energy (γ^X_S) and the interfacial energy (γ^X-Cu-_SL) of these underlayer is close to the surface energy of Cu at the melting point (γ^Cu_S (T_m)). However, the surface roughness of Cu films simultaneously increased with increasing the lateral grain size. In order to suppress the surface roughening of Cu films, post-thermal annealing procedure was applied under the ultra-high vacuum for the films fabricated on the Cr-Ni and Cr-Ni-Fe underlayers. We finally succeeded to enlarge the lateral grain diameter more than 100 nm for 50-nm-thick Cu films, maintaining a flat surface (R_a = 0.32 nm).
PMR Effect of (Cr-M)O_2 Powder Prepared by Mechanical Alloying Peer-reviewed

T. Sato, M. Tsunoda, Q. Zhang, B. Jeyadevan, M. Takahashi

Journal of Magnetic Society Japan　28　(3)　360-363　2004/03
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.28.360 　

ISSN： 0285-0192

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The powder magnetoresistance (PMR) effect of cold-pressed (Cr-M)O₂ mechanical-alloyed-powder was investigated. As additives, M, vanadium and iron were selected. The PMR ratio measured at 77 K increases from 2% to 6% with increasing iron content up to 5%, while the PMR ratio of (Cr-V)O₂ powder monotonically decreases with increasing vanadium content. Through measurement at 4.2 K, it was concluded that the changes in the PMR ratio are not due to changes in the Curie temperature of (Cr-M)O₂. The PMR effect of cold-pressed CrO₂ powder is stable up to 360°C.
Enlarged Lateral Grain Size and Reduced Surface Roughness in Metallic Thin Films Obtained by Thermal Annealing under Ultra-high Vacuum Peer-reviewed

K. Imakita, M. Tsunoda, M. Takahashi

Journal of Magnetic Society Japan　28　(3)　368-371　2004/03
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.28.368 　

ISSN： 0285-0192

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The effect of thermal annealing under ultra-high vacuum on the metallurgical microstructure of (111) -textured face-centered cubic (FCC) metal thin films was investigated. The surface morphology of 500-Å-thick metal films drastically changes with increasing annealing temperature. Regardless of the kind of metal, the morphological changes can be classified into four stages, when the annealing temperature, T_IR, is normalized by the respective melting point of the metals, T_M. In stage I , 0.15 ≤ T_IR/T_M < 0.3, the surface roughness, R_a, of metal films decreases to ∼ 3 Å. In stage II, 0.3 ≤ T_IR/T_M ≤ 0.35, remarkable grain growth occurs, and the lateral grain diameter exceeds 1000 Å. Small (∼ 200 Å) crystals appear on the large grains in the stage II', 0.35 < T_IR/T_M ≤ 0.45, and they grow large and coarsen the R_a in stage III, 0.45 < T_IR/T_M. We conclude that ultra-high vacuum annealing in stage II is effective in realizing large lateral grain size with small surface roughness in FCC metal films.
Magnetic distribution of the free layer on patterned MTJ multilayers Peer-reviewed

CG Kim, CO Kim, TS Yoon, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　268　(1-2)　271-276　2004/01

DOI： 10.1016/S0304-8853(03)00489-X 　

ISSN： 0304-8853
Correlation between Oxidization Process of Al Film for Magnetic Tunnel Junctions and Oxidizing Species in the Microwave-Excited Plasma Peer-reviewed

S. Yoshimura, M. Tsunoda, S. Ogata, M. Takahashi

Journal of Magnetic Society of Japan　27　(12)　1130-1134　2003/12
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.27.1130 　

ISSN： 0285-0192

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Langmuir probe diagnosis and optical emission spectroscopy were performed for microwave-excited plasma in order to clarify the physical factor in changing the transport properties of Co-Fe / AI-O / Co-Fe magnetic tunnel junctions (MTJs) fabricated with Ar+O₂, Kr+O₂, He+O₂ plasma. The main results were as follows: (1) Kr reduces the electron temperature of plasma at the substrate position, minimizing the ion irradiation damage during formation of an ultra-thin Al-O barrier. (2) The oxidizing species excited in plasma, such as O-radicals and O₂-ions, are drastically changed with changes in the inert gas species mixed with oxygen. The maximum energy of oxidizing species corresponds closely to the energy level of inert gas radicals. (3) O(2p)¹D radicals, which have a long life, are effectively produced in Kr+O₂ plasma and lead to a high oxidization rate of A1 films.
Thermal Stability of GMR in Co/Cu Multilayers Fabricated on bcc Solid Solution Buffer Layers Peer-reviewed

D. Takahashi, T. Sato, M. Tsunoda, M. Takahashi

Journal of Magnetics Society Japan　27　(8)　905-909　2003/08
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.27.905 　

ISSN： 0285-0192

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The thermal stability of the giant magnetoresistance (GMR) effect was examined in Co/Cu multilayers fabricated on various buffer layers with differing interfacial roughnesses and crystallographic orientations. In multilayers on body-centered cubic (BCC)-Cr₉₀Ni₁₀ and (BCC)-Cr₈₀Fe₂₀ buffer layers, the MR ratio is maintained at over 50% up to the annealing temperature of 300°C. On the other hand the MR ratio of the multilayer fabricated on δ-Cr₆₃(Ni-Fe)₃₇ buffer layer and that of the multilayer fabricated with introducing impurity oxygen into the sputtering atmosphere, decreased significantly after the thermal annealing at relatively lower temperature. Secondary ion mass spectroscopy (SIMS) analysis for the multilayer on (BCC)-Cr₉₀Ni₁₀ buffer layer shows a very small amount of atomic diffusion of buffer layer elements into the multilayer after thermal annealing, in comparison with data for multilayers fabricated on a δ-Cr₆₃(Ni-Fe)₃₇ buffer layer. Through detailed structural analysis of the multilayers, it was concluded that the interfacial flatness at grain boundaries should be improved to prevent atomic inter-diffusion and to achieve high thermal stability of the GMR effect in Co/Cu multilayers.
Body centered cubic buffer layers for enhanced lateral grain growth of Co/Cu multilayers Peer-reviewed

M Tsunoda, D Takahashi, M Takahashi

JOURNAL OF APPLIED PHYSICS　93　(10)　6513-6515　2003/05

DOI： 10.1063/1.1543877 　

ISSN： 0021-8979
Method for the synthesis of CrO2 at ambient pressure and temperature Peer-reviewed

H Ye, Q Zhang, F Saito, B Jeyadevan, K Tohji, M Tsunoda

JOURNAL OF APPLIED PHYSICS　93　(10)　6856-6858　2003/05

DOI： 10.1063/1.1555988 　

ISSN： 0021-8979
Direct synthesis of fct-FePt nanoparticles by chemical route Peer-reviewed

B Jeyadevan, K Urakawa, A Hobo, N Chinnasamy, K Shinoda, K Tohji, DDJ Djayaprawira, M Tsunoda, M Takahashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS　42　(4A)　L350-L352　2003/04

DOI： 10.1143/JJAP.42.L350 　

ISSN： 0021-4922
Material Problems in Soft-Magnetic Underlayers with High Stray-Field Stability Using Interlayer Magnetic Coupling Peer-reviewed

S. Saito, K. Hirai, A. Hashimoto, M. Tsunoda, M. Takahashi

Journal of Magnetic Society Japan　27　(4)　224-229　2003/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.27.224 　

ISSN： 0285-0192

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To reduce the spike noise caused by stray magnetic fields, we investigated layered stacking soft-magnetic underlayers (SULs) with interlayer magnetic coupling. To reduce SUL noise as well, nanocrystalline or amorphous materials are used in the large part of the soft-magnetic layer. Through investigation of material problems in ferromagnetic (FM)/nonmagnetic (NM) stacked SULs and antiferromagnetic (AFM)/ferromagnetic (FM) stacked SULs, the following points were clarified: (1) In the case of FM/NM stacked layers using Ru as the NM layer and CoZrNb as the FM layer, when the layer structure of CoZrNb (150 nm)/Ru (0.6 nm)/CoZrNb (150 nm) was adopted, the M-H loop was shifted due to RKKY interlayer exchange coupling. The value of the interlayer exchange coupling constant J was derived at a small value of 0.015 erg/cm². (2) In the above layer structure, by sputtering the Ru layer under At + O₂ atmosphere, or by introducing a Co₇₀Fe₃₀ layer which has high saturation magnetization M_s, between the Ru layer and CoZrNb layer, the value of H_ex and J were enhanced. The J value shows prospects of enhancement over one digit if appropriate materials and process are introduced. (3) In AFM/FM stacked SULs, the unidirectional anisotropy constant J_k between the AFM and FM layers was reduced by increasing the thickness of the FM layer. The principal problem is how to suppress the reduction of J_k by controlling the soft magnetic properties of the FM layer.
[INVITED] Microstructure Control Processes for Metallic Thin Films : Grain Size Control for Ultra High Density Magnetic Storage Devices

TSUNODA Masakiyo, TAKAHASHI Migaku

ITE Technical Report　27　1-6　2003
Publisher: The Institute of Image Information and Television Engineers
DOI： 10.11485/itetr.27.2.0_1 　

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The ultra-clean sputtering process (UC-process), which has been developed by the present authors, is an indispensable infrastructure for the precise control of the microstructure of metallic thin films. Developing new thin film fabrication techniques under the UC-process, the authors succeeded to control the grain size of the magnetic thin films for ultra-high-density magnetic storage devices. In the present paper, we demonstrate the enlarged in-plane grain diameter in Co/Cu mutilayers and the sharpened grain size distribution in magnetic recording media, by using novel buffer layers and ultra-thin seed layers, respectively. The guiding principles for the material design of such buffer and seed layers are also presented.
Magnetotransport Properties of Co-Fe/Al-O/Co-Fe Tunnel Junctions Oxidized with Microwave Excited Plasma Invited Peer-reviewed

K.Nishikawa, S.Ogata, T.Shoyama, W.-S.Cho, T.-S.Yoon, M.Tsunoda, M.Takahashi

Journal of Magnetics　7　(3)　63-71　2002/12
Local Variation of Magnetic Parameters of the Free Layer in TMR Junctions Invited Peer-reviewed

C.G.Kim, T.Shoyama, M.Tsunoda, M.Takahashi, T.H.Lee, C.-O.Kim

Journal of Magnetics　7　(3)　72-79　2002/12
Exchange Anisotropy of Polycrystalline Ferromagnetic / Antiferromagnetic Bilayers Invited Peer-reviewed

M.Tsunoda, M.Takahashi

Journal of Magnetics　7　(3)　80-93　2002/12
Magnetic anisotropy of antiferromagnet and its role on the exchange bias in ferromagnetic/antiferromagnetic bilayers Peer-reviewed

M Takahashi, M Tsunoda

JOURNAL OF PHYSICS D-APPLIED PHYSICS　35　(19)　2365-2376　2002/10

DOI： 10.1088/0022-3727/35/19/307 　

ISSN： 0022-3727
New plasma source with low electron temperature for fabrication of an insulating barrier in ferromagnetic tunnel junctions Peer-reviewed

K Nishikawa, M Tsunoda, S Ogata, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　38　(5)　2718-2720　2002/09

DOI： 10.1109/TMAG.2002.803167 　

ISSN： 0018-9464
Effect of an Fe-Si buffer layer on the magnetoresistance of a Co/Cu multilayer Peer-reviewed

S Miura, D Takahashi, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　91　(7)　4461-4467　2002/04

DOI： 10.1063/1.1459105 　

ISSN： 0021-8979
Effect of Interlayer Coupling on the Magnetization Process of a Free Layer in Spin-Valve Films Peer-reviewed

K. Imakita, M. Tsunoda, M. Takahashi

Journal of Magnetics Society of Japan　26　(4)　418-421　2002/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.26.418 　

ISSN： 0285-0192

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The effect of the interlayer coupling field (H_in) on the magnetization process of a free layer in spin valves (SVs) is discussed. SVs of the form Sub./Ta/Ni-Fe/Mn-Ir/Co-Fe/Cu/Ni-Fe/Cu/Ta, were used. The H_in was varied by changing the thicknesses of the free Ni-Fe and Cu spacer layers. The dynamic differential susceptibility (DDS) was measured to investigate the magnetic properties of the free layer, such as a uniaxial magnetic anisotropy field H_K and a structure constant S. As a result, it was found that even when H_in is compensated by an external applied field, S increases with the strength of the interlayer coupling, causing a deterioration of the magnetic softness of the free layer.
60% magnetoresistance at room temperature in Co-Fe/Al-O/Co-Fe tunnel junctions oxidized with Kr-O-2 plasma Peer-reviewed

M Tsunoda, K Nishikawa, S Ogata, M Takahashi

APPLIED PHYSICS LETTERS　80　(17)　3135-3137　2002/04

DOI： 10.1063/1.1475363 　

ISSN： 0003-6951
Magnetic Anisotropy of antiferromagnet in exchange coupled Ni-Fe/Mn-Ni epitaxial bilayers Peer-reviewed

M Tsunoda, M Konoto, M Takahashi

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH　189　(2)　449-457　2002/02

DOI： 10.1002/1521-396X(200202)189:2<449::AID-PSSA449>3.0.CO;2-0 　

ISSN： 0031-8965
Enhanced lateral grain growth and enlarged giant magnetoresistance in Co/Cu multilayer by Fe-Si buffer layer Peer-reviewed

D Takahashi, S Miura, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　239　(1-3)　282-284　2002/02

DOI： 10.1016/S0304-8853(01)00608-4 　

ISSN： 0304-8853
Extra large unidirectional anisotropy constant of Co-Fe/Mn-Ir bilayers with ultra-thin antiferromagnetic layer Peer-reviewed

M Tsunoda, K Nishikawa, T Damm, T Hashimoto, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　239　(1-3)　182-184　2002/02

DOI： 10.1016/S0304-8853(01)00519-4 　

ISSN： 0304-8853
Exchange anisotropy of ferromagnetic/antiferromagnetic bilayers: intrinsic magnetic anisotropy of antiferromagnetic layer and single spin ensemble model Peer-reviewed

M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　239　(1-3)　149-153　2002/02

DOI： 10.1016/S0304-8853(01)00574-1 　

ISSN： 0304-8853
Computational study in synthetic ferrimagnetic coupled media Peer-reviewed

T Michalke, DD Djayaprawira, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　239　(1-3)　22-24　2002/02

DOI： 10.1016/S0304-8853(01)00517-0 　

ISSN： 0304-8853
Interactive effect of impurities on giant magnetoresistance of Co-Fe/Cu multilayers Peer-reviewed

M Tsunoda, H Arai, D Takahashi, S Miura, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　240　(1-3)　189-191　2002/02

DOI： 10.1016/S0304-8853(01)00753-3 　

ISSN： 0304-8853
Correlation between the exchange bias and the degree of ordering of antiferromagnetic layer in PtMn/Co-Fe bilayers Peer-reviewed

T Sato, M Tsunoda, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　240　(1-3)　277-279　2002/02

DOI： 10.1016/S0304-8853(01)00827-7 　

ISSN： 0304-8853
Enhancement of exchange bias in Mn-Ir/Co-Fe based spin valves with an ultrathin Cu underlayer and in situ Mn-Ir surface modification Peer-reviewed

K Yagami, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　89　(11)　6609-6611　2001/06

DOI： 10.1063/1.1357146 　

ISSN： 0021-8979
Role of oxygen in the film growth and giant magnetoresistance of Co/Cu multilayers Peer-reviewed

S Miura, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　89　(11)　6308-6313　2001/06

DOI： 10.1063/1.1367877 　

ISSN： 0021-8979
Effects of Initial Growth of Ni-Fe Layer on Ta Film on the Structure and Magnetic Poperties of Spin Valves Grown on It Peer-reviewed

K. Yagami, K. Imakita, M. Tsunoda, M. Takahashi

Journal of Magnetics Society of Japan　25　(4-2)　811-814　2001/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.25.811 　

ISSN： 0285-0192

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The structure and magnetic properties of Mn-Ir/Co-Fe based bottom-type spin valves (SVs) were investigated as a function of the under-layer thickness. Surface morphology of Ta/Ni-Fe under layers was also investigated with in-situ STM. The SV characteristics, such as magnetoresistance (MR) ratio and interlayer ferromagnetic coupling field (H_in), strongly depend on the underlaid Ni-Fe thickness (d_Ni-Fe). The MR ratio gradually increases with decreasing d_Ni-Fe above 20 Å because of the reduction of shunting current in the Ni-Fe layer. On the contrary, the MR ratio decreases with decreasing d_Ni-Fe below 20 Å. The H_in drops below 20 Å of d_Ni-Fe and shows relatively small values (10 to 20 Oe). These changes of SV characteristics correspond closely to change in film structure: a strong fcc (111) texture of the SV is observed when d_Ni-Fe = 20 Å, but it vanishes when d_Ni-Fe < 20 Å, meaning the grain size is reduced. The surface morphology of a Ta/Ni-Fe under layer also changes drastically at d_Ni-Fe = 20 Å. Distinct grains are observed on the surface of the dNi-Fe under layer on Ta only when d_Ni-Fe = 20 Å. This indicates that inter-diffusion of the Ni-Fe layer is less than 20 Å thick with a Ta layer. We conclude that the drastic change of film structure resulting in the change of SV characteristics is due to the inter-diffused Ni-Fe-Ta layer, which promotes the grain growth of the remaining Ni-Fe layer and the SV grown on it.
GMR in Ci-Fe/Cu Multilayers Fabricated under Sputtering Atmosphere with a Small Oxygen Impurity Introduced Peer-reviewed

S. Miura, H. Arai, M. Tsunoda, M. Takahashi

Journal of Magnetics Society of Japan　25　(4-2)　815-818　2001/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.25.815 　

ISSN： 0285-0192

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Co-Fe/Cu multilayers having Cu layer thickness in the second peak of MR oscillation were fabricated under a sputtering atmosphere with a small amount of oxygen introduced as an impurity. Their giant magnetoresistance effect was investigated as a function of the partial pressure of oxygen introduction, P_O2, from 3×10^-10 Torr to 1×10^-6 Torr. Magnetoresistance (MR) ratio increased with increasing P_O2 up to 5×10^-8 Torr. The surface roughness decreased from 6 Å to 2 Å with increasing P_O2. Such changes of MR ratio and surface roughness versus P_O2 correspond closely to the changes in Co/Cu multilayers having Cu layer thickness in the first peak of MR oscillation. The maximum field sensitivity of 0.28 % / Oe was obtained at P_O2 = 1×10^-7 Torr.
Reversible Change of Direction of the Exchange Anisotropy of Polycrystalline Ferromagnetic/Antiferromagnetic Bilayers by Thermal Aneealing in Magnetic Field Peer-reviewed

M. Tsunoda, T. Hashimoto, M. Konoto, M. Takahashi

Journal of Magnetics Society of Japan　25　(4-2)　827-830　2001/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.25.827 　

ISSN： 0285-0192

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The magnetic torque of ferromagnetic/antiferromagnetic (F/AF) bilayers was analyzed to elucidate the single spin ensemble model (SSE model) as a mechanism of directional control of exchange anisotropy by thermal annealing in a magnetic field. An Ni-Fe 50 Å/Mn₇₄Ir₂₆ 50 Å polycrystalline bilayer, having a blocking temperature of 220°C, was annealed at 280°C for one hour, then cooled to room temperature under an external applied field, H_a = 1 kOe. This procedure was performed four times in succession on the same bilayer, changing the H_a direction. Exchange anisotropy was induced along the respective H_a directions, while their strength did not change at all. The reversible induction of the exchange anisotropy is well explained by the change of distribution of AF spin directions of the Mn-Ir grains, according to the SSE model. We conclude that the two-dimensional random distribution of magnetic anisotropy axes of the AF grains in the film plane, used in the SSE model, is an indispensable factor in controling the direction of exchange anisotropy of F/AF bilayers.
Ultra-clean sputtering process for magnetic thin films on hard disk drives Peer-reviewed

M Takahashi, M Tsunoda, H Shoji

VACUUM　59　(2-3)　814-824　2000/11

DOI： 10.1016/S0042-207X(00)00352-3 　

ISSN： 0042-207X
Magnetic anisotropy and rotational hysteresis loss in exchange coupled Ni-Fe/Mn-Ir films Peer-reviewed

M Tsunoda, Y Tsuchiya, T Hashimoto, M Takahashi

JOURNAL OF APPLIED PHYSICS　87　(9)　4375-4388　2000/05

DOI： 10.1063/1.373081 　

ISSN： 0021-8979
Magnetic anisotropy in antiferromagnetic layers affecting exchange bias of Ni-Fe/Mn-Ir bilayers Peer-reviewed

K Yagami, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　87　(9)　4930-4932　2000/05

DOI： 10.1063/1.373206 　

ISSN： 0021-8979
Single spin ensemble model for the change of unidirectional anisotropy constant by annealing on polycrystalline ferromagnetic/antiferromagnetic bilayers Peer-reviewed

M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　87　(9)　4957-4959　2000/05

DOI： 10.1063/1.373214 　

ISSN： 0021-8979
Field independent rotational hysteresis loss on exchange coupled polycrystalline Ni-Fe/Mn-Ir bilayers Peer-reviewed

M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　87　(9)　6415-6417　2000/05

DOI： 10.1063/1.372723 　

ISSN： 0021-8979
Extremely clean sputtering process for spin valves: exchange anisotropy and spin-dependent transport Peer-reviewed

M Takahashi, M Tsunoda, K Uneyama

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　209　(1-3)　65-70　2000/02

DOI： 10.1016/S0304-8853(99)00647-2 　

ISSN： 0304-8853
Epitaxial Growth of Ni-Fe/Mn-Ni Bilayers on MgO Single-Crystal Substrates by Facing Targets Sputtering Method. Peer-reviewed

M.Konoto, M.Tsunoda, M.Takahashi

Journal of the Magnetics Society of Japan　24　(4)　631-634　2000
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.24.631 　

ISSN： 0285-0192

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Ni-Fe / Mn-Ni bilayers were fabricated at room temperature on MgO{100} and MgO{110} single-crystal substrates by the facing-targets dc sputtering method. The Ni-Fe layer was deposited by applying a bias voltage. After the deposition of the Ni-Fe layer, an Mn-Ni layer was deposited on the Ni-Fe layer. The Ni-Fe and γ-Mn-Ni layers were grown by epitaxy and highly oriented in their crystal axes in the film plane. In the case of the MgO{100} substrate, the preferred orientations of Ni-Fe and γ-Mn-Ni were (001), and the directions of Ni-Fe[100] and γ-Mn-Ni[100] were parallel to MgO[100]. The crystal structure of γ-Mn-Ni was fct, and c/a decreased from 1.01 to 0.984 when the Mn-Ni layer thickness increased from 200 to 1000 Å. In the case of the MgO{110} substrate, the preferred orientations of Ni-Fe and γ-Mn-Ni were (110), and the directions of Ni-Fe[001] and γ-Mn-Ni[001] were parallel to the direction of MgO[001]. The crystal structure of γ-Mn-Ni was fct (c/a = 0.978).
Magnetic Anisotropy of the Antiferromagnetic Layer of Ni-Fe/Mn-Ni Exchange-Couplied Epitaxial Bilayers Determined by Magnetic Torque Analysis Peer-reviewed

M.Konoto, M.Tsunoda, M.Takahashi

Journal of the Magnetics Society of Japan　24　(4)　635-638　2000
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.24.635 　

ISSN： 0285-0192

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The magnetic anisotropy of the antiferromagnetic layer of Ni-Fe/Mn-Ni exchange-coupled bilayers was investigated by magnetic torque analysis. The Ni-Fe/Mn-Ni bilayers were highly oriented in their crystal-lographical axes in the film plane by epitaxial growth on MgO{110} single-crystal substrate. The magnetic anisotropy energy estimated from the saturated amplitude of torque curves is 6.4 x 10⁵ erg/cm³. The symmetry of the magnetic anisotropy reflects the crystallographic symmetry of the antiferromagnetic layer. The easy axis of the magnetic anisotropy is independent of the direction of the applied field during the film deposition. We conclude that the origin of the magnetic anisotropy of the antiferromagnetic layer is magnetocrystalline anisotropy.
Structure and Exchange Anisotropy of Evaporated Ni-Fe/Mn-(Ni-Fe) Films Peer-reviewed

M.Konoto, T.Sato, M.Tsunoda, M.Takahashi

Journal of the Magnetics Society of Japan　24　(4)　639-642　2000
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.24.639 　

ISSN： 0285-0192

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The correlation between the microstructure of the antiferro-magnetic (AF) layer and the unidirectional anisotropy constant (J_k) measured at room temperature was investigated for Ni-Fe 500 Å/Mn_1-x(Ni-Fe)_x 500 Å (x = 0.2-0.5) bilayers. The bilayers were fabricated on the glass substrate with and without a 60-Å-thick Ti buffer layer by the vacuum evaporation method. In the bilayers fabricated directly on the glass substrate, the grain size of the AF layer was about 120 Å and J_k was about 0.02 erg/cm² in the as-deposited state, when x = 0.2-0.3. On the other hand, when the Ti bufffer layer was used, the grain size of the AF layer was enlarged to 200 Å, and J_k was enhanced to 0.06 erg/cm². After annealing at 280°C, the J_k value of the bilayer using the Ti buffer layer reached 0.18 erg/cm², which is 1.5 times larger than without the Ti buffer layer. We concluded that enlargement of the AF grain is one of key factors for enhancing the exchange anisotropy of a ferromagnetic/AF bilayer.
Effect of Ir content and sputtering conditions on unidirectional anisotropy of Ni-Fe/Mn-Ir films fabricated under the extremely clean sputtering process Peer-reviewed

K Yagami, M Tsunoda, S Sugano, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　35　(5)　3919-3921　1999/09

DOI： 10.1109/20.800708 　

ISSN： 0018-9464
Extremely Clean Sputtering Process for Spin-Valve GMR Films Invited Peer-reviewed

M. Takahashi, M.Tsunoda

Journal of Magnetic Society of Japan　23　(7)　1841-1847　1999/07
Publisher:
ISSN： 0285-0192

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To induce adequate magnetic properties in metallic thin-film devices such as recording media and heads, it is becoming more and more important to control their microstructure. Since impurities in the sputtering atmosphere strongly affect the initial film growth, a highly purified atmosphere is required for thin-film device fabrication, in order to improve the microstructural controllability of the sputter-deposition process. In the present study, we developed a specialized multi-sputtering and used it to fabricate ultrathin spin-valve GMR films. The newly developed sputtering system makes it possible a 10^<-12> Torrvacuum condition and to supply ultra-clean processing gases. An MR ratio of 9.7% was achieved in an optimized spin-valve, sub./Ta/Ni-Fe/Co/Cu/Co/Mn-Ir/Ta, even with a total thickness of only 148Å except for the capping Ta layer. When the same structure was fabricated by degrading the base pressure of chamber to 10^<-7> Torr, the exchange-biasing effect was no longer observed, and the MR ratio suddenly dropped to 0.9%. The extremely clean sputtering process is concluded to be highly effective for realizing ultra-thin-film devices with excellent magnetic properties.
Drastic change of giant magnetoresistance of Co/Cu multilayer by decreasing residual impurities in sputtering atmosphere Peer-reviewed

S Miura, M Tsunoda, T Nagatsuka, S Sugano, M Takahashi

JOURNAL OF APPLIED PHYSICS　85　(8)　4463-4465　1999/04

DOI： 10.1063/1.370375 　

ISSN： 0021-8979
Enhanced exchange anisotropy of Ni-Fe/Mn-Ni bilayers fabricated under the extremely clean sputtering process Peer-reviewed

M Tsunoda, K Uneyama, T Suzuki, K Yagami, M Takahashi

JOURNAL OF APPLIED PHYSICS　85　(8)　4919-4921　1999/04

DOI： 10.1063/1.369142 　

ISSN： 0021-8979
Orientational dependence of the exchange biasing in Ni-Fe/Mn1-xNix (x = 0.11, 0.18, 0.23) bilayers Peer-reviewed

M Konoto, M Tsunoda, M Takahashi

JOURNAL OF APPLIED PHYSICS　85　(8)　4925-4927　1999/04

DOI： 10.1063/1.369144 　

ISSN： 0021-8979
Effect of antiferromagnetic grain size on exchange anisotropy in Ni-Fe/25at%Ni-Mn films Peer-reviewed

Masakiyo Tsunoda, Migaku Takahashi

Journal of the Magnetic Society of Japan　23　(1)　173-175　1999
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.23.173 　

ISSN： 0285-0192

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The correlation between the antiferromagnetic (AF) grain volume, ν_AF and the exchange anisotropy is discussed for Ni-Fe/25 at% Ni-Mn system. In spite of various thickness combination of ferromagnetic (F) and AF layers, the unidirectional anisotropy constant, J_k commonly became large and saturated with increasing ν_AF. The substantial coercivity originated from the AF layer decreased and became constant with increasing ν_AF. These experimental results were well explained by a simple model based on Meiklejohn's single spin model. We concluded that increasing ν_AF is key to induce the exchange anisotropy effectively in F/AF bilayers.
Initial Growth of Cu Films Fabricated by Sputtering and Evaporation Peer-reviewed

M. Tsunoda, M. Ashino, M. Takahashi, T. Shiba

Journal of the Magnetics Society of Japan　23　(4)　1233-1236　1999
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.23.1233 　

ISSN： 0285-0192

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Microstructural changes in the initial growth stage of Cu films fabricated by sputtering and evaporation are discussed. During and after deposition, the amplitude V of surface acoustic waves (SAWs) propagated on the piezoelectric substrate through the films deposited on it, and the electrical sheet resistivity of the films, R_sq, were measured. The surface morphology of the films was examined by using an atomic force microscope. As a result, it was found that (1) the critical thicknesses d_p, at which the islands of a film begin to percolate, and d_c, at which the film becomes two-dimensionally continuous, are smaller in sputter-deposited films than in evaporated ones; (2) the surface roughness of sputter-deposited films is smaller than that of evaporated films; and (3) microstructural change that increases the average inter-island spacing is harder to achieve in sputter-deposited films than in evaporated ones.
Microstructure and Giant Magnetoresistance of Ag-Co Films Fabricated by Means of an Extremely Clean Sputtering Process (Compared with Cu-Co Films) Peer-reviewed

M. Tsunoda, D. Takahashi, H. Okahara, M. Takahashi

Journal of the Magnetics Society of Japan　23　(4)　1341-1344　1999
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.23.1341 　

ISSN： 0285-0192

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The influence of impurities in the sputtering atmosphere on the microstmcture and giant magnetoresistance (GMR) of Ag_100-xCo_x (x = 0-62 at%) thin films was investigated Ag-Co films were prepared on quartz substrates at room temperature, varying the purity of the sputtering atmosphere by changing the base pressure, with 10^-11 Torr for an extremely clean process (XC-process) and 10^-7 Torr for a lower-grade process (LG-process). The correlation between the microstructure and the GMR of Ag-Co films after annealing is discussed It was found that (1) the precipitation of Co particles progressed in the as-deposited films, and the degree of supersaturantion of the matrix phase in the LG-processed films was higher than that in the XC-processed films; (2) the size of the Co particles precipitated in the as-deposited LG-processed films was larger than that in the XC-processed films, and resulted in a higher MR ratio of the as-deposited LG-processed films than that of the XC-processed ones under a maximum applied field of 14 kOe; (3) the magnitude of the MR ratio in the XC-processed films after annealing above 300°C was larger than that in the LG-processed ones, apparently because of the homogeneity of the Co particles of the precipitate.
Influence of impurity gas in the sputtering atmosphere on the microstructure and the GMR in Co/Cu multilayers Peer-reviewed

S Miura, D Takahashi, M Tsunoda, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　34　(4)　936-938　1998/07

DOI： 10.1109/20.706319 　

ISSN： 0018-9464
Microstructure and giant magnetoresistance of Co-Cu granular films fabricated under the extremely clean sputtering process Peer-reviewed

M Tsunoda, K Okuyama, M Ooba, M Takahashi

JOURNAL OF APPLIED PHYSICS　83　(11)　7004-7006　1998/06

DOI： 10.1063/1.367625 　

ISSN： 0021-8979
Percolation and Continuation Thickness of Ag Films on the Initial Growth Stage Peer-reviewed

M.Tsunoda, T.Ito, M.Takahashi, T.Shiba

J. Magn. Soc. Jpn.　22　(4-2)　453-456　1998/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.22.453 　

ISSN： 0285-0192

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Growth of vapor-deposited Ag films by the coalescence process in the post-nucleation stage is discussed. During and after deposition, the amplitude V of surface acoustic waves (SAW) propagated on the piezoelectric substrate through the films deposited on it, and the electric sheet resistivity of the films, R_sq, were measured. The microstructures of films with various thicknesses d were examined with a scanning electron microscope. As a result, it was found that (1) the thickness d_p at which V reaches a minimum value corresponds to the critical thickness at which the islands of a film begin to percolate, (2) the thickness d_c at which 1/R_sq begins to be proportional to the film thickness corresponds to the critical thickness at which the film becomes two-dimensionally continuous, (3) d_p and d_c become larger with decreasing deposition rate, and (4) in the early coalescence stage (d<d_p), the microstructural change progresses, increasing the average inter-island spacing. From these results, we can conclude that a higher deposition rate is necessary to suppress the microstructural change of islands and to allow fabrication of continuous ultra-thin films.
Structural Changes in Ultra-thin Ag Films Evaporated on a Cr Seed Layer Peer-reviewed

M.Tsunoda, T.Ito, M.Takahashi, T.Shiba

J. Magn. Soc. Jpn.　22　(4-2)　457-460　1998/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.22.457 　

ISSN： 0285-0192

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Structural change in vapor-deposited Ag films on a ultra-thin (< 10 Å) Cr seed layer during the coalescence process is discussed. During and after the deposition, the amplitude of surface acoustic waves (SAW) propagated on the piezoelectric substrate through the films deposited on it and the electric sheet resistivity of the films were measured. The microstructures of films with various thicknesses, d were examined with a scanning electron microscope. As a result, we found that (1) the critical thick-nesses d_p at which the islands of film begin to percolate and d_c at which the film becomes two-dimensionally continuous drastically decreased with increasing seed layer thickness, but (2) Ag films flattened by the Cr seed layer spontaneously tore when the deposition was interrupted at a thickness between d_p and d_c. We conclude that two-dimensionally continuous ultra-thin Ag films thinner than 120Å can be prepared on a 3-Å-thick Cr seed layer by continuous deposition.
Structure and GMR in Ni-Fe/Cu Multilayers Fabricated by an Ultra-clean Sputtering Process Peer-reviewed

M.Tsunoda, T.Miyata, S.Miura, M.Takahashi

J. Magn. Soc. Jpn.　22　(4-2)　545-548　1998/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.22.545 　

ISSN： 0285-0192

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The relation between the dry-etching time of the substrate and the magnetoresistance (MR) is discussed for Ni-Fe/Cu multilayers fabricated by a facing-targets sputtering method. The role of the underlying, Ta, Fe, Ni-Fe, or Ni-Fe fabricated in an N₂ mixed sputtering atmosphere (Ni-Fe (N₂)), is also discussed from the viewpoint of the relation between the microstructure and the GMR properties. Dry etching of the substrate surface with RF plasma before film deposition results in a remarkable increase in the MR ratio. An underlying 30-Å-thick Ta layer increased the MR ratio, while a 5-Å-thick Ni-Fe (N₂) underlayer decreased it From an analysis of the structure and magnetic properties of the multilayers, it is concluded that enlargement of the grain diameter in the multilayers led to an enhancement of the interlayer magnetic coupling, and resulted in the remarkable increase in the MR ratio
Effect of surface cleaning of substrate on the exchange coupling field in Ni-Fe/25at%Ni-Mn films Peer-reviewed

M Tsunoda, M Konoto, K Uneyama, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　33　(5)　3688-3690　1997/09

DOI： 10.1109/20.619539 　

ISSN： 0018-9464
Influence of gas adsorption at the interface on the exchange coupling field of Ni-Fe/25at%Ni-Mn/Ni-Fe films Peer-reviewed

K Uneyama, M Tsunoda, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　33　(5)　3685-3687　1997/09

DOI： 10.1109/20.619538 　

ISSN： 0018-9464
Microstructure of antiferromagnetic layer affecting on magnetic exchange coupling in trilayered Ni-Fe/25 at% Ni-Mn/Ni-Fe films Peer-reviewed

M Tsunoda, Y Tsuchiya, M Konoto, M Takahashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　171　(1-2)　29-44　1997/07

DOI： 10.1016/S0304-8853(97)00054-1 　

ISSN： 0304-8853
(Effect of gas adsorption onto the interface on the exchange-coupling field of Ni-Fe/25at%Ni-Mn Film Peer-reviewed

釆山和弘, 角田匡清, 甲野藤真, 高橋研

J. Magn. Soc. Jpn.　21　(4-2)　517-520　1997/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.21.517 　

ISSN： 0285-0192

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The effect of gas adsorption onto the interface on the exchange-coupling field of Ni-Fe/25 at%Ni-Mn film was investigated. Ni-Fe/25 at%Ni-Mn/Ni-Fe trilayer films were prepared on an Si(100) substrate by a facing-targets sputtering method. The lower interface of trilayer films was exposed for 1 hour in various atmospheres controlled by introducing air or N₂ through a variable leak valve. The strength of the exchange coupling, J_k, decreased rapidly when the air pressure during exposure exceeded 1×10^-7 Torr. From the temperature dependence of J_k and cross-sectional TEM observation, it was found that γ-Ni-Mn became easy to separate into α-Mn+θ-NiMn with increasing air pressure, leading to the decrease in J_k at R.T. This structural change in Ni-Mn layer was considered to be caused by the H₂O/O₂ gas adsorption or partial oxidation on the lower Ni-Fe surface, preventing epitaxial growth of γ-Ni-Mn grain on it.
(Effect of substrate surface cleaness on GMR in Co/Cu multilayers) Peer-reviewed

M.Tsunoda, S.Miura, K.Uneyama, M.Takahashi

J. Magn. Soc. Jpn.　21　(4-2)　553-556　1997/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.21.553 　

ISSN： 0285-0192

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The correlation between the cleanness of the substrate and the magnetoresistance (MR) is discussed for Co/Cu multilayers fabricated by a facing-targets sputtering method. Dry-etching of the substrate surface with RF plasma before film deposition results in a remarkable increase in the MR ratio, especially in multilayers whose Cu space layer thickness (d_cu) is from 9Å to 11Å. From an analysis of the structure and magnetic properties of multilayers, it was concluded that an enlargement of the grain diameter in the multilayers led to an enhancement of the interlayer magnetic coupling, and resulted in the remarkable increase in the MR ratio. An exposing study of dry-etched substrates under various atmospheres, confirmed that dry-etching desorbed H₂O and/or O₂ gases from the surface and enhanced the mobility of sputtered adatoms on it.
Effect of the surface cleaning of the substrate on the exchange-coupling field of an Ni-Fe/25at%Ni-Mn film Peer-reviewed

M.Tsunoda, M.Konoto, K.Uneyama, M.Takahashi

J. Magn. Soc. Jpn.　21　(4)　513-516　1997
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.21.513 　

ISSN： 0285-0192

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The effect of gas adsorption onto the substrate on the exchange-coupling field of an Ni-Fe/25 at%Ni-Mn/Ni-Fe film was investigated. Trilayer films were prepared on an Si(100) substrate by the facing-targets sputtering method. The strength of the exchange coupling, J_k, at R.T. increased rapidly when the substrate surface was etched with RF plasma. From analysis of the structure of films, and in view of the temperature dependence of J_k, it was concluded that the increase in J_k was caused by enlargement of the in-plane diameter of γ-Ni-Mn grains epitaxially grown on underlaid Ni-Fe grains. From an exposing study of dry-etched substrate in various atmospheres, dry- etching was considered to desorb H₂O and/or O₂ gasses from the surface and to enhance the mobility of sputtered adatoms, thus causing enlargement of the underlaid NiFe grain size.
Magnetic Properties of Exchange-Coupled Ni-Fe/25at% Ni-Mn Films Peer-reviewed

M.Tsunoda, Y.Tsuchiya, M.Takahashi, T.Wakiyama

J. Magn. Soc. Jpn.　20　(2)　393-396　1996/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.20.393 　

ISSN： 0285-0192

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Ni-Fe/25 at%Ni-Mn/Ni-Fe trilayer films were prepared on Si(100) substrate by the facing-targets sputtering method. Unidirectional magnetic anisotropy, induced by exchange coupling at the interface between the Ni-Fe and Ni-Mn layers, was observed in the Ni-Fe layer. The strength of the exchange coupling, J_k, was about 0.07 erg/ cm² at R. T. and fell to 0 when the film was heated above 170°C (blocking temperature, T_B). As a result of field cooling in the direction opposite to the easy direction initially induced, the sign of J_k changed from positive to negative, even at temperatures less than T_B. This change in J_k suggests that the Néel temperatures of grains at the interface were broadly distributed.
Influence of Metal Seed Layers on Initial Film Growth Peer-reviewed

M.Tsunoda, M.Takahashi, N.Yamada, T.Wakiyama, T.Shiba

Journal of Magnetic Society Japan　20　(2)　321-324　1996/02
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.20.321 　

ISSN： 0285-0192

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Ag and Cu films were deposited by vacuum evaporation on a LiNbO₃ single-crystal substrate on which surface acoustic waves (SAW) at 45 MHz were propagating. Prior to the deposition, ultra-thin Ti, Cr, Cu, and Ag films were fabricated as seed layers. The coalescence processes in an earlier stage of the film growth were investigated by measuring the SAW amplitudes during deposition. The critical thickness, at which the film structure changes from islandlike to continuous, was found to decrease with increasing seed thickness, except in the case of Cu films deposited on Ag seed layers. Ag films deposited on ultra-thin seed layers had topologically smooth surfaces in comparison with films directly deposited on the substrate. These results suggest that islands of the seed layer capture the adatoms diffused over the substrate surface and become the growth centers for the subsequent film deposition.
Initial Growth of Metal Films Fabricated on a Substrate Excited by SAW Peer-reviewed

M.Tsunoda, N.Yamada, M.Takahashi, T.Wakiyama, T.Shiba

J. Magn. Soc. Jpn.　19　(2)　317-320　1995/04

DOI： 10.3379/jmsjmag.19.317 　
GIANT MAGNETO-OPTICAL TRANSITION FOR Pt SUBSTITUTED MnSb FILMS WITH NiAs STRUCTURE (Invited) Peer-reviewed

M.TAKAHASHI, H.SHOJI, M.TSUNODA, S.SAITO, T.WAKIYAMA, Y.TAKEDA, Y.ITAKURA

Journal of the Magnetic Society of Japan　19, S1　(1)　23-28　1995
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.19.S1_23 　

ISSN： 0285-0192

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MnSbPt films (thickness of 1000Å) with the concentration of 50at%Mn. 44at%Sb and 6at%Pt annealed 300°C showed giant Kerr rotation angle of about 0.9° at short wavelength of λ=500nm. The results of structural analysis with X-ray and NMR revealed that the giant Kerr rotation angle observed in present films is closely related to the MnSb compound including Pt atom in NiAs structure. The experiments using powder alignment samples prepared under external magnetic field showed that the direction of the easy axis of magnetization of present MnSbPt with NiAs structure was found to change from c-plane to c-axis with increasing Pt concentration.
RECENT NEW EXPERIMENTS IN MAGNETIC THIN-FILM FABRICATION - PLASMA NITRIDING AND SAW EXCITING SUBSTRATE Invited Peer-reviewed

M TAKAHASHI, H SHOJI, M TSUNODA

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　134　(2-3)　403-418　1994/06

DOI： 10.1016/0304-8853(94)00151-0 　

ISSN： 0304-8853
Fabrication and Structure Controllability of Metal Films with a Substrate Excited by SAW Peer-reviewed

M.Tsunoda, M.Takahashi, S.Sakakibara, T.Wakiyama, T.Shiba

J. Magn. Soc. Jpn.　18　(2)　289-294　1994/04

DOI： 10.3379/jmsjmag.18.289 　
Giant Magnetoresistance in Co/Cu Multilayers Prepared by Vacuum Evaporation and Sputtering Methods Peer-reviewed

M. Tsunoda, M. Takahashi, T. Miyazaki

IEEE Translation Journal on Magnetics in Japan　9　(3)　133-140　1994

DOI： 10.1109/TJMJ.1994.4565870 　

ISSN： 0882-4959
SURFACE-TOPOLOGY OF METALLIC-FILMS FABRICATED ONTO SUBSTRATES EXCITED BY SURFACE ACOUSTIC-WAVES Peer-reviewed

M TAKAHASHI, S SAKAKIBARA, M TSUNODA, H SHOJI, T WAKIYAMA

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　126　(1-3)　62-64　1993/09

DOI： 10.1016/0304-8853(93)90546-E 　

ISSN： 0304-8853
Giant Magnetoresistance in Co/Cu Multilayers Prepared by Vacuum Evaporation and Sputtering Methods. Peer-reviewed

M.Tsunoda, M.Takahashi, T.Miyazaki

J. Magn. Soc. Jpn.　17　(5)　826-831　1993
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.17.826 　

ISSN： 0285-0192

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Co/Cu multilayers were prepared on a glass substrate by both vacuum evaporation and sputtering methods. Pure Cu films were also prepared by the same methods. The surface morphology and resistivity were investigated in order to determine the influence of the preparation methods on the film structure. The MR ratio oscillates with the Cu layer thickness, d_Cu, in sputtered multilayers prepared at low Ar pressure (15 mTorr), whereas it increases monotonically with d_Cu in sputtered multilayers prepared at high Ar pressure (50 mTorr). On the other hand, the MR ratio oscillates with d_Cu only beyond 20Å in evaporated multilayers prepared at a high deposition rate (2Å/s). The MR ratio of the samples prepared at a low deposition rate (0.5Å/s) almost disappears. The AFM investigation of the multilayers and Cu films indicates the existence of a rumpling of the layered structure, with a waving period of 100Å～500Å. The fluctuation of the rumpling is large in multilayers evaporated at a low rate (0.5Å/s) and small in multilayers sputtered at low pressure (15 mTorr). The difference in the MR ratio between the samples prepared by the two methods and in the different conditions is mainly due to the difference of the multilayer stacking structures.
SYNTHESIS OF METAL HYDROXIDE-LAYER SILICATE INTERCALATION COMPOUNDS (METAL = MG(II), CA(II), MN(II), FE(II), CO(II), NI(II), ZN(II), AND CD(II)) Peer-reviewed

K OHTSUKA, M SUDA, M TSUNODA, M ONO

CHEMISTRY OF MATERIALS　2　(5)　511-517　1990/09

DOI： 10.1021/cm00011a009 　

ISSN： 0897-4756
EPITAXIAL-GROWTH OF NICKEL(II) HYDROXIDE ON LAYER SILICATE AND DERIVED NICKEL (LAYER SILICATE) NANOCOMPOSITE Peer-reviewed

K OHTSUKA, J KOGA, M TSUNODA, M SUDA, M ONO

JOURNAL OF THE AMERICAN CERAMIC SOCIETY　73　(6)　1719-1725　1990/06

DOI： 10.1111/j.1151-2916.1990.tb09819.x 　

ISSN： 0002-7820

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Misc. 109

Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect in A Model with Crystal Field (vol 84, 094710, 2015)

Satoshi Kokado, Masakiyo Tsunoda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　86　(10)　2017/10

DOI： 10.7566/JPSJ.86.108001 　

ISSN： 0031-9015
19aAU-10 Gigantic spin waves in perpendicularly magnetized ferrimagnetic GdFeCo thin film induced by pulsed light excitation

Ohkochi T, Schneider C. M, Kuroda H, Arguelles E. F, Sakaue M, Kasai H, Suga S, Kinoshita T, Fujiwara H, Kotsugi M, Adam R, Takahashi H, Tsunoda M, Tsukamoto A, Sekiyama A, Nakamura T

Meeting Abstracts of the Physical Society of Japan　71　(0)　1005-1005　2016
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.71.1.0_1005 　

ISSN： 2189-079X
招待講演 Fe₄N擬単結晶薄膜の異方性磁気抵抗効果と異常ホール効果 (磁気記録・情報ストレージ)

角田匡清, 鹿原和樹, 古門聡士

電子情報通信学会技術研究報告 = IEICE technical report : 信学技報　115　(263)　11-14　2015/10/22
Publisher: 電子情報通信学会
ISSN： 0913-5685
21pPSA-33 Composition- and temperature-dependence of laser-induced magnetization reversal of ferrimagnetic GdFeCo studied by soft X-ray photoemission microscopy

Yagi T, Osawa H, Schneider Claus M, Sekiyama A, Suga S, Kinoshita T, Ohkochi T, Fujiwara H, Kotsugi M, Adam Roman, Takahashi H, Tsunoda M, Tsukamoto A, Nakamura T

Meeting Abstracts of the Physical Society of Japan　70　(0)　1106-1106　2015
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.70.1.0_1106 　

ISSN： 2189-079X
27aPS-121 Development of measurement system for magneto-optical effect with a vacuum ultraviolet High harmonic Generation laser

Yamamoto Sh., Someya T., Itatani J., Hobara R., Fujisawa M., Yoshida R., Yamamoto T., Nakamura T., Tsunoda M., Yamamoto S., Shin S., Matsuda I.

Meeting abstracts of the Physical Society of Japan　69　(1)　503-503　2014/03/05
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
7pPSA-26 Laser-induced magnetization reversal of ferrimagnetic GdFeCo studied by soft X-ray photoemission microscopy

Yagi T, Osawa H, Schneider Claus M, Sekiyama A, Suga S, Kinoshita T, Ohkochi T, Fujiwara H, Kotsugi M, Adam Roman, Takahashi H, Tsunoda M, Tsukamoto A, Nakamura T

Meeting Abstracts of the Physical Society of Japan　69　(0)　279-279　2014
Publisher: The Physical Society of Japan
ISSN： 1342-8349
Anisotropic Magnetoresistance Effect in Ferromagnet :Magnetization Direction Dependence in A Model with Crystal Field

Kokado S., Tsunoda M.

Meeting abstracts of the Physical Society of Japan　68　(2)　365-365　2013/08/26
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
26pEJ-10 Development of measurement system for magneto-optical effect with a vacuum ultraviolet SASE free electron laser

Yamamoto S., Fujisawa M., Hobara R., Yamamoto S., Nakamura T., Fujikawa K., Yukawa R., Taguchi M., Oura M., Togashi T., Tsunoda M., Shin S., Matsuda I.

Meeting abstracts of the Physical Society of Japan　68　(1)　801-801　2013/03/26
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
18pPSA-10 Theoretical Study of Anisotropic Magnetoresistance Effects is Ferromagnets : Magnetization Direction Dependence in A System with Crystal Field of Cubic Symmetry

Kokado S., Tsunoda M., Harigaya K., Sakuma A.

Meeting abstracts of the Physical Society of Japan　67　(2)　402-402　2012/08/24
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
21aPS-19 Theoretical Study of Anisotropic Magnetoresistante Effects in Various Ferromagnets

Kokado S., Tsunoda M., Harigaya K., Sakuma A.

Meeting abstracts of the Physical Society of Japan　66　(2)　376-376　2011/08/24
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
Fe₄N薄膜の放射光メスバウアー分光測定

壬生攻, 角田匡清, 瀬戸誠, 駒崎洋亮, 田中雅章, 北尾真司, 小林康浩, 依田芳卓

日本物理学会講演概要集　66　(1)　485-485　2011/03/03
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
28aHE-4 Light induced magnetization switching of perpendicularly magnetized GdFeCo film using pulsed Laser

大河内拓雄, 福島和亮, 山口淳一, 磯上慎二, 中村哲也, 児玉謙司, 藤原秀紀, 菅滋正, 木下豊彦, 小嗣真人, 角田匡清, 塚本新, 関山明, 新井邦明

Meeting Abstracts of the Physical Society of Japan　66　(0)　938-938　2011
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.66.1.4.0_938_2 　

ISSN： 1342-8349
23pJB-12 Light induced magnetization switching of perpendicularly magnetized CdFeCo film using pulsed Laser

大河内拓雄, 福島和亮, 山口淳一, 磯上慎二, 中村哲也, 児玉謙司, 藤原秀紀, 菅滋正, 木下豊彦, 小嗣真人, 角田匡清, 塚本新, 関山明, 新井邦明

Meeting Abstracts of the Physical Society of Japan　66　(0)　936-936　2011
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.66.2.4.0_936_3 　

ISSN： 1342-8349
パルスマグネットを用いた強磁場軟X線MCD測定技術の開発

中村哲也, 鳴海康雄, 広野等子, 児玉謙司, 林美咲, 磯上慎二, 高橋宏和, 角田匡清, 伊東航, 梅津理恵, 金道浩一, 貝沼亮介, 野尻浩之, 木下豊彦

日本磁気学会学術講演概要集　34th　83　2010/09/04

ISSN： 1882-2959
22pGL-11 Sign of the interface exchange coupling and the direction of Ir magnetization induced in Co_<1-x>Fe_x/MnIr exchange bias films by resonant magnetic scattering at the Ir L_3 absorption edge

Hosoito Nobuyoshi, Yamagishi Ryuichiro, Kodama Kenji, Takahashi Hirokazu, Tsunoda Masakiyo

Meeting abstracts of the Physical Society of Japan　65　(1)　955-955　2010/03/01
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
Development of High Performance Mn-Ir based Exchange Anisotropy Materials

M. Tsunoda

Magnetics Japan　5　(3)　115-126　2010/03
Publisher: Magnetic Society of Japan
ISSN： 1880-7208
20aHS-8 Observation of Co/Pt magnetic dots by hard X-ray Fourier transform holography

Suzuki M, Kondo Y, Takahashi S, Isogami S, Tsunoda M, Ishio S

Meeting Abstracts of the Physical Society of Japan　65　(0)　968-968　2010
Publisher: The Physical Society of Japan
ISSN： 1342-8349
23pRG-8 Development of soft x-ray MCD measurement technique using pulsed high magnetic field

Nakamua Tetsuya, Umetsu Rie, Kindo Koichi, Kainuma Ryosuke, Nojiri Hiroyuki, Kinoshita Toyohiko, Narumi Yasuo, Hirono Toko, Kodama Kenji, Hayashi Misaki, Isogami Shinji, Takahashi Hirokazu, Tsunoda Masakiyo, Ito Wataru

Meeting Abstracts of the Physical Society of Japan　65　(0)　683-683　2010
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.65.2.4.0_683_3 　

ISSN： 1342-8349
CS-8-1 Materials and Processes for Reproducing Heads of Ultra-high Density Hard Disk Drives

Tsunoda Masakiyo, Takahashi Migaku

Proceedings of the IEICE General Conference　2009　(2)　"S-59"-"S-60"　2009/03/04
Publisher: The Institute of Electronics, Information and Communication Engineers
28pRE-8 Development of hard X-ray Fourier transform holography

Suzuki M., Isogami S., Tsunoda M., Nomura K., Awaji N., Nakamura T.

Meeting Abstracts of the Physical Society of Japan　64　(0)　955-955　2009
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.64.1.4.0_955_4 　

ISSN： 1342-8349
Extreme Nano-structure Control by Sputtering for the High Density Perpendicular Recording Media and Head

Migaku Takahashi, Masakiyo Tsunoda, Shin Saito

ECS Transactions　16　(45)　19-35　2009

DOI： 10.1149/1.3140007 　
Orientational Control of Barrier Layer with Interfacial Modification and Its Effect on Tunnel Magnetoresistance in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

M. Tsunoda, M. Takahashi

Journal of the Vacuum Society of Japan　51　(9)　583-588　2008/10
Publisher: The Vacuum Society of Japan
DOI： 10.3131/jvsj2.51.583 　

ISSN： 1882-2398

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Crystallographic orientation of the MgO barrier in sputter-deposited CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) and its effect on tunnel magnetoresistance (TMR) were investigated. The degree of MgO(001) orientation was estimated with the integral intensity ratio (I₍₂₀₀₎/I₍₂₂₀₎) of diffraction lines from MgO(200) and MgO(220) planes obtained in grazing incident x-ray diffraction profiles. The main results are stated as follows. (1) I₍₂₀₀₎/I₍₂₂₀₎~4, meaning the (001) orientation of MgO, is realized when the underlaid CoFeB maintains amorphous structure, meanwhile MgO on bcc(110)-oriented CoFe shows (111) orientation (I₍₂₀₀₎/I₍₂₂₀₎=0). (2) The prevention of epitaxial growth on hcp(00.1)-oriented Ru layer is effective to maintain amorphous structure of CoFeB. (3) The achievable TMR ratio after high temperature (280°C-450°C) annealing is mainly dominated by the MgO orientation and giant TMR ratio exceeding 200% is only obtained with I₍₂₀₀₎/I₍₂₂₀₎≥3.4, while the resistance area product is independent of I₍₂₀₀₎/I₍₂₂₀₎.
22aPS-22 Feasibility study of magnetic imaging using the Fourier transformed holography method

Nakamura T., Suzuki M., Awaji N., Doi S., Nomura K., Isogami S., Tsunoda M.

Meeting Abstracts of the Physical Society of Japan　63　(0)　655-655　2008
Publisher: The Physical Society of Japan
DOI： 10.11316/jpsgaiyo.63.2.4.0_655_1 　

ISSN： 1342-8349
24pWK-9 Measurement of induced spin polarization of Ir at an interface of an exchange biased CoFe/Mnlr bilayer by resonant x-ray magnetic reflectivity

Kodama K, Hosoito N, Yamagishi R, Tsunoda M, Isogami S

Meeting Abstracts of the Physical Society of Japan　63　(0)　482-482　2008
Publisher: The Physical Society of Japan
ISSN： 1342-8349
Facile synthesis, phase transfer, and magnetic properties of monodisperse magnetite nanocubes

J. U. Cho, D. K. Kim, T. X. Wan, S. Isogami, M. Tsunoda, M. Takahashi, Y. K. Kim

IEEE Transaction on Magnetics　44　(11)　2547-2550　2008

DOI： 10.1109/TMAG.2008.2001786 　
交換バイアス反強磁性材料

角田匡清

KINZOKU Materials Science & Technology　77　(9)　58-65　2007/09
Publisher: アグネ技術センター
21pWD-2 Investigation of an gigantic magnetic moment of Fe_<16>N_2 thin layer using polarized neutron diffraction measurements

Takeda Masayasu, Kakurai Kazuhisa, Sunaga Kazuyuki, Tsunoda Masakiyo, Takahashi Migaku

Meeting abstracts of the Physical Society of Japan　62　(2)　436-436　2007/08/21
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
機能性薄膜作製のためのスパッタリングターゲット―技術課題と今後への指針―

高橋研, 斉藤伸, 角田匡清

真空　50　(1)　22-27　2007/01
Publisher: 日本真空協会
Mn3Ir反強磁性合金による巨大交換バイアス

角田匡清, 三俣千春, 中村哲也, 高橋研

日本応用磁気学会第150回研究会資料　19-28　2006
超高密度ストレージ用極薄磁性膜の微細組織・界面制御

高橋研, 角田匡清, 斉藤伸

表面技術　56　(10)　558-564　2005/11
Publisher: The Surface Finishing Society of Japan
DOI： 10.4139/sfj.56.558 　

ISSN： 0915-1869
Giant Exchange Anisotropy of Mn₃Ir/Co-Fe Bilayers

M. Tsunoda, K. Imakita, M. Takahashi

Journal of Magnetic Society of Japan　29　(7)　722-731　2005/07
Publisher: 日本応用磁気学会
ISSN： 0285-0192

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The exchange anisotropy of Mn_<1-x>Ir_x/Co_<70>Fe_<30> bilayers fabricated on a Cu or Ru underlayer while changing the substrate temperature (T_) during the deposition of the Mn-Ir layer was investigated in relation to the crystallographic structure of the Mn-Ir layer. The unidirectional anisotropy constant (J_K) of bilayers with x=0.27 varied markedly as a function of T_. After thermal annealing of the bilayers at 320℃ in a magnetic field of 1 kOe, J_K increased steeply from 0.3erg/cm^2 to 1.3erg/cm^2 as T_ was raised from room temperature to 170℃. The blocking temperature was simultaneously enhanced from 270℃ to 360℃. X-ray diffraction profiles showed that ordered Mn_3Ir phase was formed in the antiferromagnetic layer as T_ was increased. Giant J_K and the formation of Mn_3Ir phase were observed in bilayers within the range 0.22≤x≤0.32. The coincidence of the enhanced J_K and the increased degree of order of the Mn-Ir layer strongly suggests that the Mn_3Ir phase is the origin of the giant J_K and the high blocking temperature. The dependence of the exchange anisotropy of polycrystalline Mn_3Ir/Co_<70>Fe_<30> bilayers on the antiferromagnetic layer thickness (d_<AF>) was also investigated, and the following findings were obtained. A maximum unidirectional anisotropy constant (J_K) of 1.3erg/cm^2 is obtained at d_<AF>=10nm. The critical thickness of d_<AF>, where J_K becomes half of its maximum value, is less than 5nm, and is comparable to that of a bilayer containing disordered Mn-Ir. The blocking temperature (T_B) is enhanced by several tens of degrees as a result of the ordering of the Mn-Ir layer.
Mn-Ir / Co-Fe積層膜の巨大交換磁気異方性

角田匡清, 今北健一, 高橋研

日本応用磁気学会第140回研究会資料　11-19　2005
Interface flattening of giant magnetoresistance (GMR)/tunnel magnetoresistance (TMR) multilayers by oxygen addition in their sputter-deposition process

Masakiyo Tsunoda, Migaku Takahashi

Shinku/Journal of the Vacuum Society of Japan　48　(1)　34-38　2005
Publisher: Vacuum Society of Japan
DOI： 10.3131/jvsj.48.34 　

ISSN： 0559-8516
Magnetization reversal of the ferromagnetic layer in exchange-coupled Mn-Ir/Co-Fe epitaxial bilayers

SATO T., TSUNODA M., SHIBATA M., NAKA M., TAKAHASHI M.

28　424-424　2004/09/21
Giant exchange anisotropy observed in polycrystalline Mn-Ir/Co-Fe bilayers

IMAKITA K., TSUNODA M., TAKAHASHI M.

28　426-426　2004/09/21
Temperature Dependence of Magnetic Anisotropy of Antiferromagnetic Layer of Exchange-Coupled Mn-Ir/Ni-Fe Epitaxial Bilayers

TSUNODA M., SHIBATA M., SATO T., TAKAHASHI M.

28　425-425　2004/09/21
Synthesis and magnetic moment of γ'-Fe-N/Cu multilayer with various N contents

SUNAGA K., TSUNODA M., TAKAHASHI M.

28　503-503　2004/09/21
Ferromagnetic tunnel junctions fabricated with high concentration ozone oxidization method

YOSHIMURA S., NARISAWA Y., TSUNODA M., TAKAHASHI M.

28　118-118　2004/09/21
Effect of nitriding species in plasma on TMR properties of magnetic tunnel junctions with Al-N barrier

TSUNODA M., SHOYAMA T., YOSHIMURA S., TAKAHASHI M.

28　114-114　2004/09/21
Fabrication of Polycrystalline Ferromagnetic Tunnel Junctions with Mg-O barrier

YOSHIMURA S., NOZAWA T., NARISAWA Y., TSUNODA M., TAKAHASHI M.

28　119-119　2004/09/21
Surface morphologies and magnetotransport properties of ferromagnetic tunnel junctions by using bottom electrode with large lateral grain size

IMAKITA K., TSUNODA M., TAKAHASHI M.

28　117-117　2004/09/21
Surface flattening of metal layer by oxygen-additive sputtering method and its effect on TMR properties of magnetic tunnel junctions

YOSHIMURA S., SHOYAMA T., NOZAWA T., TSUNODA M., TAKAHASHI M.

28　116-116　2004/09/21
Effect of ion irradiation of Al-N barrier on TMR properties of Magnetic Tunnel Junctions

TSUNODA M., WATANABE Y., IMAKITA K., YOSHIMURA S., TAKAHASHI M.

28　115-115　2004/09/21
Development of exchange bias in IrMn3 based tunnel junctions

VK Sankaranarayanan, YK Hu, CG Kim, CO Kim, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH　201　(8)　1688-1691　2004/06

DOI： 10.1002/pssa.200304540 　

ISSN： 0031-8965
Temperature dependence of exchange coupling in Mn75Ir25/Co70Fe30/AlOx/Co70Fe30/Ni80Fe20 MTjs

YK Hu, SM Yoon, JJ Lim, VK Sankaranarayanan, CG Kim, CO Kim, M Tsunoda, M Takahashi

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH　201　(8)　1700-1703　2004/06

DOI： 10.1002/pssa.200304651 　

ISSN： 0031-8965
Barrier Layer Materials for Magnetic Tunnel Junctions

M. Tsunoda, S. Yoshimura, M. Takahashi

Materia　43　(3)　492-497　2004/06
Publisher: The Japan Institute of Metals and Materials
DOI： 10.2320/materia.43.492 　

ISSN： 1340-2625
Exchange Anisotropy of Ferromagnetic/Antiferromagnetic Bilayers - Magnetic Anisotropy of Antiferromagnetic Layer and Its Role in Exchange Anisotropy -

M. Tsunoda, M. Takahashi

Journal of Magnetic Society of Japan　28　(2)　55-65　2004/02
Publisher: 日本応用磁気学会
ISSN： 0285-0192

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The origin of magnetic anisotropy of the antiferromagnetic layer and its role in the magnetization process of exchange-coupled ferromagnetic(F)/antiferromagnetic(AF) bilayers are discussed. Magnetic torque analysis of pseudo-single crystalline F/AF bilayers strongly suggests that the magnetocrystalline anisotropy of the antiferromagnet is the origin of magnetic anisotropy of the AF layer. According to the simple exchange anisotropy model established by Meiklejohn and Bean (1957), magnetic torque curves were analyzed for pseudo-single crystalline Ni-Fe/Mn-Ni and Mn-Ir/Ni-Fe bilayers, the AF layer thicknesses of which are less than the critical value necessary to induce an exchange bias field. The anisotropy energies of Mn_<82>Ni_<18> and Mn_<75>Ir_<25> were determined in (110)-(001)-, (111)-planes from the saturation torque amplitude of the pseudo-single crystalline bilayers with the respective crystallographic orientation. We introduce a single spin ensemble model for polycrystalline bilayers, taking into account the two-dimensional random distribution of the magnetic anisotropy axes of AF grains. We also successfully elucidate the exchange anisotropy features, such as blocking temperature, reversible directional control by field cooling, critical AF layer thickness, and changes of unidirectional anisotropy constant by thermal annealing, with a single spin ensemble model, in relation to the role of the magnetic anisotropy of the AF layer.
強磁性トンネル接合膜用バリア層材料とその形成プロセス

角田匡清

日本金属学会セミナー・テキスト最先端スピンエレクトロニクス技術の基礎と応用　19-27　2004
微量酸素添加成膜による極薄金属膜の平坦化技術

角田匡清, 高橋研

日本真空協会Ｈ16.6 研究例会資料　12-18　2004
Oxidation Process of Al Film by Using Microwave-Excited Plasma

YOSHIMURA S., SHOYAMA T., NOZAWA T., YOON T. S., TSUNODA M., TAKAHASHI M.

27　426-426　2003/09/01

ISSN： 1340-8100
Enhanced Lateral Grain Growth in Cu Films Fabricated on BCC Solid Solution Under Layers

IMAKITA K., TSUNODA M., TAKAHASHI M.

27　457-457　2003/09/01

ISSN： 1340-8100
Oxidization of Various Metal Films with Using Microwave-Excited Plasma

YOSHIMURA S., SHOYAMA T., TSUNODA M., TAKAHASHI M.

27　427-427　2003/09/01

ISSN： 1340-8100
Ferromagnetic Tunnel Junctions Fabricated with Microwave Exicited Plasma Nitridation Method (II)

TSUNODA M., SHOYAMA T., YOSHIMURA S., NOZAWA T., TAKAHASHI M.

27　428-428　2003/09/01

ISSN： 1340-8100
Reduced Surface Roughness and Increased Lateral Grain Size in Metallic Thin Films by Post IR-heat Treatment

IMAKITA K., TSUNODA M., TAKAHASHI M.

27　456-456　2003/09/01

ISSN： 1340-8100
Exchange anisotropy of Mn-Ir/Co-Fe epitaxial bilayers with different crystallographic orientation

SATO T., TSUNODA M., TAKAHASHI M.

27　17-17　2003/09/01

ISSN： 1340-8100
Changes of exchange anisotropy of polycrystalline Mn-Ir/Co-Fe bilayers by long-time anneal

SATO T., TSUNODA M., TAKAHASHI M.

27　16-16　2003/09/01

ISSN： 1340-8100
Enhancement of lateral grain growth by novel buffer layer and fabrication process of tunnel barriers by using microwave-excited plasma

TSUNODA M., IMAKITA K., YOSHIMURA S., TAKAHASHI M.

132　33-41　2003

ISSN： 1340-7562
Enhancement of lateral grain growth by novel buffer layer and fabrication process of tunnel barriers by using microwave-excited plasma

角田匡清, 今北健一, 吉村哲, 高橋研

日本応用磁気学会第132回研究会資料　33-41　2003
金属磁性薄膜の微細組織制御プロセス―超高密度ストレージ用薄膜の粒径制御

角田匡清, 高橋研

信学技報　MR2002　74　2003
Recent trends and prospects of magnetic thin films for ultrahigh-density data storage - Control of microstructure and interface under the ultraclean process -

M. Takahashi, M. Tsunoda

OYO BUTSURI　71　(10)　1214-1226　2002/10
Publisher: 応用物理学会
ISSN： 0369-8009
Effect of Inert Gas on Magnetoresistance of Ferromagnetic Tunnel Junctions Fabricated with Microwave Excited Plasma Oxidization Method

TSUNODA M., NISHIKAWA K., YOON T. S., OGATA S., TAKAHASHI M.

26　3-3　2002/09/01

ISSN： 1340-8100
Plasma Diagnostics and Optical Emission Spectroscopy of Microwave-Excited Plasma using a RLSA

YOSHIMURA S., OGATA S., TSUNODA M., TAKAHASHI M.

26　4-4　2002/09/01

ISSN： 1340-8100
Evaluation of magnetic anisotropy of antiferromagnetic grain in Mn-Ir/Co-Fe polycrystalline bilayers

SATO T., TSUNODA M., AKIIKE T., TAKAHASHI M.

26　198-198　2002/09/01

ISSN： 1340-8100
Enhanced Lateral Grain Growth in Co/Cu Multilayers Fabricated on Fe-Si Buffer Layers

TSUNODA M., TAKAHASHI D., MIURA S., TAKAHASHI M.

26　191-191　2002/09/01

ISSN： 1340-8100
Structure and GMR effect of Co/Cu Multilayers Fabricated on BCC Solid Solution Buffer Layers

TAKAHASHI D., TSUNODA M., TAKAHASHI M.

26　192-192　2002/09/01

ISSN： 1340-8100
Effect of interlayer coupling on the magnetization process of free layer in spin-valve films

IMAKITA K., TSUNODA M., TAKAHASHI M.

25　35-35　2001/09/01

ISSN： 1340-8100
Correlation between the exchange bias and the degree of ordering of antiferromagnetic layer in PtMn/Co-Fe bilayers

SATO T., TSUNODA M., TAKAHASHI M.

25　30-30　2001/09/01

ISSN： 1340-8100
Compositional dependence of exchange anisotropy of Co_<1-x>Fe_x/Mn-Ir bilayers

TSUNODA M., NISHIKAWA K., DAMM Thorsten, HASHIMOTO T., TAKAHASHI M.

25　28-28　2001/09/01

ISSN： 1340-8100
Fablication of Ferromagnetic Tunnel Junctions Using High Density and Low Electron Temperature Plasma

NISHIKAWA K., OGATA S., TSUNODA M., TAKAHASHI M.

25　340-340　2001/09/01

ISSN： 1340-8100
高性能スピンバルブの極薄膜化に関するクリーンプロセスの意義

角田匡清, 高橋研

日本応用磁気学会研究会資料　27-33　2001
Realization of Desirable Microstructure in Functional Magnetic Thin Films by Controlling the Impurities in Sputtering Process

Migaku Takahashi, Masakiyo Tsunoda, David D. Djayaprawira

Shinku/Journal of the Vacuum Society of Japan　44　(7)　631-638　2001

DOI： 10.3131/jvsj.44.631 　

ISSN： 0559-8516
High sensitive GMR in Co-Fe/Cu multilayers fabricated under the modified sputtering atmosphere by regulating amount of impurity

MIURA S., OHNISHI H., TSUNODA M., TAKAHASHI M.

24　316-316　2000/09/01

ISSN： 1340-8100
Effect of impurities in the sputtering atmosphere on thermal stability of GMR in Co/Cu multilayers

TAKAHASHI D., MIURA S., TSUNODA M., TAKAHASHI M.

24　318-318　2000/09/01

ISSN： 1340-8100
Influence of Fe-Si buffer layer on GMR in Co/Cu multilayers

MIURA S., TAKAHASHI D., TSUNODA M., TAKAHASHI M.

24　317-317　2000/09/01

ISSN： 1340-8100
Magnetic anisotropy of antiferromagnetic layer of Ni-Fe/Mn-Ni epitaxial bilayer

KONOTO M., TSUNODA M., TAKAHASHI M.

24　406-406　2000/09/01

ISSN： 1340-8100
Enhancement of H_<ex> in Mn-Ir/Co-Fe exchange-coupled films by controlling seed layers

YAGAMI K., TSUNODA M., TAKAHASHI M.

24　409-409　2000/09/01

ISSN： 1340-8100
Reduction of ferro-coupling between pin/free layers in SV fabricated under extremely clean process

YAGAMI K., IMAKITA K., TSUNODA M., TAKAHASHI M.

24　418-418　2000/09/01

ISSN： 1340-8100
Effect of under layers on the structure and magnetic properties of spin-valve films : Examination of the morphology of Ta/Ni-Fe under layers with in-situ STM

YAGAMI K., IMAKITA K., TSUNODA M., TAKAHASHI M.

24　419-419　2000/09/01

ISSN： 1340-8100
Direction control of exchange anisotropy of polycrystalline Ni-Fe/Mn-Ir bilayers by thermal annealing in magnetic field

TSUNODA M., HASHIMOTO T., TAKAHASHI M.

24　407-407　2000/09/01

ISSN： 1340-8100
Effect of Ir content and sputtering conditions on unidirectional anisotropy of Ni-Fe/Mn-Ir films fabricated under the extremely clean sputtering process (vol 35, pg 3919, 1999)

K Yagami, M Tsunoda, S Sugano, M Takahashi

IEEE TRANSACTIONS ON MAGNETICS　36　(3)　612-612　2000/05

ISSN： 0018-9464
Structure and exchange anisotropy of Ni-Fe/Mn-Ir bilayers -Correlation between magnetic anisotropy of antiferromagnetic films and J_k-

YAGAMI K., TSUNODA M., TAKAHASHI M.

23　24-24　1999/10/01
Single spin ensemble model for reduction of unidirectional anisotropy constant of polycrystalline ferro/antiferro bilayers

TSUNODA M., TAKAHASHI M.

23　25-25　1999/10/01
Field independent rotational hysteresis loss on exchange coupled Ni-Fe/Mn-Ir bilayers

TSUNODA M., TAKAHASHI M.

23　22-22　1999/10/01
Dependence of exchange anisotropy and microstructure of Ni-Fe/Mn-Ir bilayers on deposition rate and Ir content of Mn-Ir films

YAGAMI K., TSUNODA M., SUGANO S., TAKAHASHI M.

23　23-23　1999/10/01
Exchange ansiotropy of Ni-Fe/Mn-Ni bilayers highly orientated in the film plane (II) -Magnetic torque analysis of mahnetic anisotropy of antiferromagnet-

KONOTO M., TSUNODA M., TAKAHASHI M.

23　15-15　1999/10/01
Exchange ansiotropy of Ni-Fe/Mn-lr bilayers fabricated under the extremely clean sputtering process -Change of magnetic torque curve as a function of antiferromagnetic layer thickness-

TSUNODA M., HASHIMOTO T., TSUCHIYA Y., TAMAHASHI M.

23　21-21　1999/10/01
Structure and exchange ansiotropy of evaporated Ni-Fe/Mn-(Ni-Fe)films

KONOTO M., SATO T., TSUNODA M., TAMAHASHI M.

23　16-16　1999/10/01
Influence of substrate and buffer layer on GMR in Co/Cu multilayers

MIURA S., OONISHI H., TSUNODA M., TAKAHASHI M.

23　432-432　1999/10/01
Influence of impurity gas on GMR in Co/Cu multilayers

MIURA S., TSUNODA M., TAKAHASHI M.

23　431-431　1999/10/01
Microstructure and magnetic properties of M-Co(M=Au, Ag, Cu) granular films -Influence of impurities in sputtering atmosphere on formation of solid solution-

TAKAHASHI D., OONISHI H., TSUNODA M., TAKAHASHI M.

23　375-375　1999/10/01
Exchange ansiotropy of Ni-Fe/Mn-Ni bilayers highly oriented in the film plane (I) -Epitaxial growth on MgO single crystal substrate-

KONOTO M., TSUNODA M., TAKAHASHI M.

23　14-14　1999/10/01
磁気トルク法によるNi-Fe/Mn-Ir積層膜の交換磁気異方性評価

角田匡清

日本応用磁気学会学術講演概要集　1999
極清浄雰囲気中で作製したNi-Fe/Mn-Ir積層膜の交換磁気異方性

角田匡清

第23回日本応用磁気学会学術講演概要集　1999
Microstructure and giant magnetoresistance of Ag-Co films fabricated under the extremely clean sputtering process

TSUNODA M., TAKAHASHI D., OKAHARA H., TAKAHASHI M.

22　251-251　1998/09/01
Effect of change in the crystal orientation on the exchange coupling field of Ni-Fe/Mn_<1-x>Ni_x film

KONOTO M., TSUNODA M., TAKAHASHI M.

22　193-193　1998/09/01
Influence of residual impurities in Sputtering atmosphere on GMR of Co/Cu multilayer

MIURA S., TSUNODA M., NAGATSUKA T., SUGANO S., TAKAHASHI M.

22　42-42　1998/09/01
Effect of change in the crystal orientation on the exchange coupling field of Ni-Fe/Ni-Mn film.

TSUNODA M., KONOTO M., TSUCHIYA Y., TAKAHASHI M.

21　27-27　1997/10/01
Effect of substrate surface cleaning on GMR in Co/Cu multilayers (Temperature dependence on GMR)

MIURA S., TAKAHASHI D., TSUNODA M., TAKAHASHI M.

21　441-441　1997/10/01
Influence of impurity gas in the sputtering atmosphere on GMR in Co/Cu multilayers

MIURA S., TAKAHASHI D., TSUNODA M., TAKAHASHI M.

21　442-442　1997/10/01
Structure and GMR in NiFe/Cu multilayers fabricated under ultra clean sputtering process

TSUNODA M., MIYATA T., MIURA S., TAKAHASHI M.

21　440-440　1997/10/01
Structural change in initial growth stage of Ag films evaporated on Cr seed layer

TSUNODA M., ITO T., TAKAHASHI M., SHIBA T.

21　323-323　1997/10/01
Percolation and continuation thickness of Ag films on initial growth stage

TSUNODA M., ITO T., TAKAHASHI M., SHIBA T.

21　322-322　1997/10/01
Effect of substrate surface cleanness on GMR in Co/Cu multilayers

TSUNODA M., MIURA S., UNEYAMA K., TAKAHASHI M.

20　395-395　1996/09/01
Effect of gas adsorption onto the interface on the exchange coupling field of Ni-Fe/Ni_<25>Mn_<75> film

UNEYAMA K., TSUNODA M., KONOTO M., TAKAHASHI M.

20　145-145　1996/09/01
Effect of surface cleanness of substrate on the exchange coupling field of Ni-Fe/Ni_<25>Mn_<75> film

TSUNODA M., KONOTO M., UNEYAMA K, TAKAHASHI M.

20　144-144　1996/09/01
Magnetic properties and structures of exchange-coupled Ni-Fe/Ni_5Mn_<75> films

TSUNODA M., TSUCHIYA Y., TAKAHASHI M.

20　143-143　1996/09/01
Magnetic properties of exchange coupled Ni-Fe/Ni-Mn films

TSUNODA M., TSUCHIYA Y., TAKAHASHI M., WAKIYAMA T.

19　349-349　1995/09/01
Evaluation of Seed layer effect for initial film growth(Evaluated by surface acoustic waves)

TSUNODA M., TAKAHASHI Migaku, WAKIYAMA T., SHIDA T.

19　515-515　1995/09/01
Initial growth of Ag films(Observation by using the substrate excited by SAW)

TSUNODA M., ITO T., TAKAHASHI M., WAKIYAMA T., SHIBA T.

19　512-512　1995/09/01

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Books and Other Publications 3

磁気便覧

日本磁気学会

丸善　2016/01
薄膜ハンドブック第２版

角田匡清

オーム社　2008/03

ISBN: 9784274205194
Thin Film Engineering

金原粲, 監修, 白木靖寛, 吉田貞史, 著

2003/03

Presentations 17

AMR and XMCD Study of Pseudo Single Crystal γ’-Fe4N Films International-presentation

M. Tsunoda, H. Takahashi, S. Kokado, T. Nakamura, Y. Komasaki, M. Takahashi

International Conference of AUMS, 2010　2010/12/05
Magnetic Imaging with Coherent X-rays International-presentation

M. Suzuki, T. Nakamura, N. Awaji, M. Tsunoda

International Conference of AUMS, 2010　2010/12/05
Lensless Holographic Imaging Using Hard X-rays International-presentation

Motohiro Suzuki, Yuji Kondo, Shinji Isogami, Shingo Takahashi, Shunji Ishio, Tetsuya Nakamura, Kenji Nomura, Naoki Awaji, Masakiyo Tsunoda

The 6th International Workshop on Nano-scale Spectroscopy and Nanotechnology　2010/10/25
High Performance MgO Magnetic Tunnel Junctions - Materials and Processes - International-presentation

M. Takahashi

The 4th Taiwan International Conference on Spintronics　2008/10/02
Tailor-Made Nano Structured Materials for Highly Qualified Spin Related Devices – Exchange Coupling and Spin Dynamics – International-presentation

M. Takahashi, M. Tsunoda, S. Saito, T. Ogawa

The 7th IEEE International Conference on Nanotechnology (IEEE-NANO 2007)　2008/08/02
Formation of MgO(001) barrier on amorphous CoFeB layer and giant magnetoresistance in CoFeB/MgO/CoFeB magnetic tunnel junctions International-presentation

M. Tsunoda, Y. Ashizawa, S. Isogami, H. Ohyama, K. Sunaga, M. Takahashi

The 4th Asian Conference on Crystal Growth and Crystal Technology　2008/05/21
Process and materials for high performance spintronics devices International-presentation

M. Takahashi, M. Tsunoda

The 3rd Taiwan International Conference on Spintronics　2007/07/31
Microscopic origin and a role of uncompensated antiferromagnetic spins in Mn-Ir based exchange biased bilayers International-presentation

M. Tsunoda, T. Nakamura, C. Mitsumata, M. Takahashi

1st International Symposium on Advanced Magnetic Materials and Apllications (ISAMMA 2007)　2007/05/28
Crystallographic structure and giant TMR of CoFeB/MgO/CoFeB MTJs International-presentation

M. Tsunoda, Y. Ashizawa, H. Ohyama, K. Sunaga, M. Takahashi

The 2nd RIEC International Workshop on Spintronics　2007/02/05
GIANT EXCHANGE ANISOTROPY AND HIGH BLOCKING TEMPERATURE OF Mn₃Ir/Co-Fe BILAYERS International-presentation

M. Tsunoda, M. Takahashi

6TH International Symposium on physics of Magnetic Materials (ISPMM 2005)　2005/09/14
GIANT EXCHANGE ANISOTROPY OF Mn₃Ir/Co-Fe BILAYERS International-presentation

M. Tsunoda, K. Imakita, M. Takahashi

International Symposium on Spintronics and Advanced Magnetic Technologies and International Symposium on Magnetic Materials and Applications 2005 (ISAMT/SOMMA 2005)　2005/08/24
Controlled oxidization process for ultra-thin aluminium films in high-performance magnetic tunnel junctions by using microwave-excited plasma with radial line slot antenna International-presentation

International Symposium on Magnetic Materials and Applications (SOMMA)　2003/12/03
Exchange anisotropy of ferromagnetic/antiferromagnetic bilayers -magnetic anisotropy of antiferromagnet and its role on the exchange bias - International-presentation

18th International Colloquium on Magnetic Films and Surfaces (18th ICMFS)　2003/07/22
Magnetic Anisotropy of Antiferromagnet in Exchange Coupled Ni-Fe/Mn-Ni Epitaxial Bilayers International-presentation

First Seeheim Conference on Magnetism (SCM2001)　2001/09/07

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(プロシーディング) physica. status solidi WILEY-VCH 2002 449 457
Exchange anisotropy of ferromagnetic/antiferromagnetic bilayers:intrinsic magnetic anisotropy of antiferromagnetic layer and single spin ensemble mode International-presentation

International Symposium on Physics of Magnetics 2001/International Symposium on Advanced Magnetic Technologies2001 (ISPMM/ISAMT2001)　2001/05/13

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(プロシーディング) Journal of Magnetism and Magnetic Materials elsevier 2002 149 153
Ultra clean spttering process for magnetic thin films of hard disk drives International-presentation

The Fifth International Symposium on Sputtering & Plasma Processes (ISSP'99)　1999/06/16

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(プロシーディング) VACUUM elsevier 2000 814 824
Extremely Clean Sputtering Process for Spin Valves:Exchange Anisotropy and Spindependent Transpoet International-presentation

International Symposium on Advanced Magnetic Technologies (ISAMT'99)　1999/05/24

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(プロシーディング) Journal of Magnetism and Magnetic Materials elsevier 2000 65 70

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Industrial Property Rights 8

サーミスタ

特許3622853

Property Type: Patent
サーミスタの製造方法

特許3622852

Property Type: Patent
導電性チップ型セラミック素子及びその製造方法

3036567

Property Type: Patent
酸化物半導体組成物

2658581

Property Type: Patent
チップ型サーミスタおよびその製造方法

2765237

Property Type: Patent
チップ部品の電極ペースト塗布方法

2836225

Property Type: Patent
負特性サーミスタ

2623881

Property Type: Patent
サーミスタ

2591205

Property Type: Patent

Show all Show first 5

Research Projects 31

Study on Magnetic Thin Films Competitive

System: Grant-in-Aid for Scientific Research

1991/10 - Present
量子系ワイヤレス給電に向けたスピン・分子回転・分子振動－電気伝導変換の理論研究

古門聡士, 角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(C)

Institution: 静岡大学

2024/04/01 - 2027/03/31
Development of anomalous Hall effect materials with high spin polarization for high efficiency spin-orbit-torque magnetization switching

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2024/04/01 - 2027/03/31
ナノサイズ高感度磁気再生素子を実現するＣＰＰ－ＡＭＲ単結晶薄膜材料の開発

角田匡清, 古門聡士

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(B)

Institution: 東北大学

2020/04/01 - 2023/03/31

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本年度は、昨年度検討を行ったNi-Co合金薄膜に引き続き、酸化マグネシウム単結晶基板上に、種々の組成をもつNi-Fe, Fe-Co合金薄膜をエピタキシャル成長させ、同薄膜の異方性磁気抵抗（AMR）効果の電流方位依存性について検討を行った。AMR効果の計測には、試料回転機構を有する超電導マグネット物理特性計測装置（PPMS）を用い、in-plane AMR、out-of-planeAMR、およびtransverse AMRの３種類について、室温から5Kの範囲で測定を行った。得られたAMR効果の結果を用いて、現象論的表式（W. Doring）の磁気抵抗定数（AMR係数）を算出し、Ni-Fe, Fe-Co合金薄膜の同定数の組成ならびに温度依存性を決定した。磁気抵抗定数の算出には、付加的効果が重畳しやすいと考えられるin-plane AMRの実験結果を用いない表式を導出して用いた。 Ni-Fe合金薄膜では、インバー合金組成付近のNi30～40at%の試料でAMR効果が小さくなることが判った。これはfcc, bccの相境界付近でフェルミ準位のアップスピン電子、ダウンスピン電子のd軌道の状態密度の差が小さくなることと対応しており、Kokadoらが構築した電子散乱理論と定性的に一致する。また、Fe-Co合金では、電流方向//Fe-Co[100]と電流方向//Fe-Co[110]の場合で、AMR効果に差があることが判った。これはZengら（PRL125(2020)097201）の報告に一致しており、磁化方向変化によるバンド構造変化による効果である可能性があることが判った。理論の側面からは、in-plane AMR, out-of-plane AMR, transverse AMRの測定結果に対応すべく、厳密対角化の手法を用いて各方位のAMR効果の数値解析を行った。
超高周波ワイヤレス給電に向けたスピンを介した分子運動－電気伝導変換の理論的研究

古門聡士, 角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(C)

Institution: 静岡大学

2019/04/01 - 2023/03/31

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本研究は局在スピンを介した分子運動－伝導電子間相互作用Vに関する理論的研究である．このVの構築には，Vに大きな影響を与える伝導(s)電子からd軌道への遷移確率(s-d散乱)を詳細に調べる必要がある．s-d散乱を調べる手法として，電気抵抗が磁化方向に依存する現象である異方性磁気抵抗(AMR)効果がある．今回我々は「1. 電流と磁化が任意の方向の場合の強磁性体の電気抵抗率ρの式の導出」及びそれを用いた「2. Strong ferromagnetのFe4NのIn-plane AMR効果とTransverse AMR効果の計算」を行った．主な結果は次の通りである． 1. 以前我々が開発した不純物による電子の散乱理論を用いて，電流と磁化が任意の方向の場合の強磁性体のρの式を導出した．特にStrong ferromagnetではρ∝PεDε+PγDγとして表された．ただし，Dε(Dγ)はフェルミ準位上のdown spinのdε(dγ)軌道の部分状態密度，Pε(Pγ)はdown spinのdε(dγ)軌道の電流方向の確率密度を表し，Pε+Pγ=一定を満たす．Dε=Dγのときρは磁化方向に依らず一定であり，Dε≠Dγのときρは磁化方向に依った． 2. 上記ρを用いて，立方対称結晶場を持つFe4NのIn-plane AMR効果とTransverse AMR効果を調べた．ここでは以前Fe4Nに対して評価されたDε/Dγ=1.22を用いた．電流(x方向)と磁化の相対角をθとするとき，In-plane AMR効果は2回対称(cos2θ)成分を持つ負のAMR, Transverse AMR効果は4回対称(cos4θ)成分を持つ正のAMRが得られた．これらの結果はT=50KでのFe4Nの実験結果と定性的によく合うことが確認された．
Nitride based coherent heterostructures for efficient spin-orbit torque magnetization switching

ISOGAMI Shinji

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: National Institute for Materials Science

2019/04/01 - 2022/03/31

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To achieve remarkable reduction of critical current density (Jc) for magnetization switching in magnetic thin films, the Mn-based nitrides (Mn-N) were examined and the switching demonstration was performed in this study. In addition to the switching in heterostructures with Pt layers, magnetization switching was succeeded even in the Mn-N single layer, which was the significant results beyond the earlier expectation. The Jc of Mn-N was one order of magnitude smaller than that of CoFeB conventional magnetic thin films. These results show the great significance on the prospect that neither heterostructure nor magnetic tunnel junctions might be necessary for magnetic memories, resulting in the enhancement of high integration with simple architectures that has not been demonstrated.
Theoretical Study on Transformation between Electric Power and Motive Power Mediated by Spin for Electricity Self-Generation Type Nanomachine

Kokado Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: Shizuoka University

2016/10/21 - 2020/03/31

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"Electric generation type nanomachine", in which motions can be properly remote-controlled and travel motions are performed by the self-generated electric power, needs the mutual transformation between electron conduction and molecular motions. We proposed an idea that interactions between electrons and molecular motions mediated by localized spins can be used in the transformation. To formulate this V, we must find properties of s-d scatterings from the conduction (s) electron to the localized d orbitals. In this study, we theoretically studied the s-d scattering and anisotropic magnetoresistance (AMR) effect, which directly reflects the s-d scattering. We first developed the s-d scattering theory for a model with the crystal field, and then qualitatively explained experimental results of the AMR effects for Ni, Fe, and half-metal, which had not been explained by conventional theories.
Development of ferromagnetic tunnel junctions with a ferroelectric barrier layer and the control of their spin-transport by electric field effects

TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2014/04/01 - 2017/03/31

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This study is aimed to control the spin-transport in Fe4N-based ferromagnetic tunnel junctions through the electric field effect by spontaneous polarization of a ferroelectric tunnel barrier. Various kinds of anti-perovskite-type transition-metal nitride thin films were successfully synthesized and their magnetic and magneto-transport properties were examined. The spin-polarized transport theory was newly constructed taking into account the spin-orbit interaction and crystal field effects, and successfully evaluated the spin-polarization of conduction electrons in ferromagnets with its sign through the anisotropic magnetoresistance effects. Epitaxial growth technique of thin films was developed for complex oxides as perovskite-type ferroelectrics. Electric field effects of ferromagnetic tunnel junctions with a ferroelectric barrier layer were investigated by the first-principles calculation.
Theoretical Study on Generation and Control of Molecular Motion by Spin for Magnetic Molecular Machine

KOKADO SATOSHI

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: Shizuoka University

2013/04/01 - 2017/03/31

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Toward generation and remote control of the motion "molecular oscillation and rotation" in a magnetic molecular machine, we performed a theoretical study on a relaxation of an excited spin. Here, the relaxation is considered to originate from a spin-molecular motion (oscillation and rotation) interaction V. For this V, spin direction dependence of 3d orbitals with spin-orbit interaction and crystal field plays an important role. In addition, a phenomenon to observe such dependence is the anisotropic magnetoresistance (AMR) effect. In this study, we theoretically investigated the spin-direction dependence of the 3d orbitals and the AMR effect. As a result, we obtained new insights about the spin-direction dependence of shape of the 3d orbitals and the crystal field effect on the AMR ratio.
Magnetic damping control of ferromagnetic thin films with negative spin polarization and development of highly efficient spin-current generator

ISOGAMI Shinji, TSUNODA Masakiyo, OOGANE Mikihiko, SAKUMA Akimasa

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Young Scientists (B)

Institution: Fukushima National College of Technology

2012/04/01 - 2015/03/31

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Highly efficient spin-current generator was developed using Fe4N thin films with negative spin polarization. The high quality Fe4N/Pt bilayer films were fabricated by the reactive sputtering with Ar and N2 gas mixture during thermal treatment using the focused IR heating system. The electromotive force due to inverse spin-Hall effect generated by spin-pumping from the Fe4N films exhibited one order larger value, compared with the NiFe conventional films. The results implied that our developed Fe4N/Pt systems provided highly spin-current generator.
Development of spintronics devices with using negative spin polarization materials

TSUNODA Masakiyo, KOKADO Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2011/04/01 - 2014/03/31

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We succeeded for the single phase synthesis of Mn4N and Co3FeN thin films that have isomorphic structure to Fe4N showing negative spin polarization. The Mn4N thin films exhibited perpendicular magnetic anisotropy. We constructed a theory for anisotropic magnetoresistance (AMR) effects, which takes into account the spin-orbit interaction and the crystal field splitting. Negative AMR ratio observed for the Co3FeN thin films indicated a possibility of them to be half-metals. Inverse tunnel magnetoresistance effects were observed for Fe4N-based magnetic tunnel junctions with a spinel tunnel barrier. High efficiency for spin current generation under ferromagnetic resonance was suggested for Fe4N/Pt bilayers by their large inverse spin Hall signals.
Creation of Spin-Nanostructure with Extreme High Magnetic Moment

TAKAHASHI Migaku, TSUNODA Masakiyo, OGAWA Tomoyuki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (S)

Institution: Tohoku University

2009/05/11 - 2014/03/31

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In order to obtain a new magnetic material with high saturation magnetization, establishment of synthesis method of alpha"-Fe16N2 nanoparticles and fabrication method of Fe-based nanoparticle assembly. By synthesizing new precursors and optimizing process conditions, single-phase of alpha"-Fe16N2 nanoparticles was successfully synthesized for the first time, whose saturation magnetization was 234emu/g. By applying Fe nanoparticles with 10nm in diameter, newly developed coagulation method of nanoparticles could control a volume fraction from 0.5% to 40% of the Fe nanoparticle assembly.
Fabrication of full metal CPP-spin valves with atomic order spacer layer and their magnetoresistance effect

TSUNODA Masakiyo, TAKAHASHI Hirokazu

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Tohoku University

2011 - 2012

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In order to develop a multilayer material in which magnetic moments steeply change their direction within atomic-order thickness, current-perpendicular to plane (CPP) magnetoresistance thin-film devices, consisted of Co based ferromagnetic layer and Ru spacer layer, were fabricated with UHV-sputtering method, and their transport properties were investigated. The interfacial uncompensated spins of Mn-Ir/ ferromagnetic bilayerswere also investigated with changing the ferromagnetic material. As a result, the exchange interaction at the interface and crystal structure of the ferromagnet were found to be important for large exchange anisotropy.
窒化鉄薄膜を用いた高効率スピン源の開発

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 特定領域研究

Institution: 東北大学

2009 - 2010

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理論研究によれば、Fe_4Nはいわゆるハーフメタルではないが、その電気伝導度のスピン偏極率は-1であり、小数スピンの電子が伝導を担っている。また、Fe_4N/MgO/CoFeBの構造を有する強磁性トンネル接合(MTJ)では、室温で最大-75%のインバースTMR効果が観測されており、Fe_4N中での少数スピン伝導がその起源と考えられている。また、平成21年度までの研究により、Fe_4N薄膜で観測される負のAMR効果は、伝導電子の負のスピン分極を反映したものであることが明らかとなっている。そこで、本年度は、引き続きFe_4N単結晶薄膜のAMR効果ならびにFe_4N/MgO/CoFeB-MTJの電流誘起磁化反転(CIMS)について検討を行った。スパッタ法により、MgO単結晶基板上に100nm厚のFe_4N単結晶膜を作製しAMR効果の結晶方位依存性を調べた。その結果、AMR比は電流を[100]方向に流した場合に低温で負に大きく増大するのに対して、[110]方向に流した場合には増大は見られないことが判った。これは、Fe_4Nの軌道磁気モーメントが磁化結晶方位依存性をもつとする理論計算の結果を勘案し、スピンー軌道相互作用を介して軌道磁気モーメントがAMR効果に影響を及ぼした結果であることが示唆された。Fe_4N/MgO/CoFeB-MTJのCIMSは、正のスピン分極を有する強磁性層を両電極とした通常のCoFeB/MgO/CoFeB-MTJのそれとは異なり、亀流方向と磁化反転の方向が逆転するインバースCIMS効果を示すことが判った。また、本インバースCIMS効果はFe_4Nをフリー層とした場合に観測されており、従来の理論では説明できない現象であることも併せて明ちかとなった。
Hard-X-ray magnetic holographic imaging using coherence and polarization properties of synchrotron radiation

SUZUKI Motohiro, KONDO Yuji, TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: Japan Synchrotron Radiation Research Institute

2008 - 2010

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Lensless Fourier transform holography measurement using hard X-rays was developed to observe the magnetic domain structure in bit-patterned media for ultradense data recording, with a sub-10-nm spatial resolution. This technique used the coherence and polarization properties of synchrotron X-rays. A charge density image of the magnetic dots made of Co/Pt multilayer was successfully obtained with a 30-nm resolution. Magnetic imaging has been done but the statistical accuracy should be improved. Refinements in the experimental arrangement and analysis method are ongoing.
Development of High Performance Exchange Bias Materials by Analyzing and Controlling Interfacial Induced Uncompensated Antiferromagnetic Spins

TSUNODA Masakiyo, NAKAMURA Tetsuya, MISTUMATA Chiharu, TAKAHASHI Hirokazu

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2008 - 2010

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A correlation between uncompensated (UC)antiferromagnetic (AF)spins and exchange bias (E. B.)strength was investigated for Mn_<74> Ir_<26>/Co_<100-x> Fe_x bilayers. The E. B. strength had a maximum at x=25 at.%, and the x-ray magnetic circular dichroism of Mn, representing the UC-AF spins, changed systematically in sign and magnitude with respect to x. A linear correlation was found between the E. B. strength and the root mean square magnitude of the UC-Mn spins. The hidden parameter connecting these two quantities might be exchange coupling energy at the hetero-interface, which varies as a function of the ferromagnetic layer composition. Based on the above findings, we succeeded to induce large (> 1. 2 erg/cm^2)E. B. strength on L1_2-Mn_3Ir/Co_<65> Fe_<35> bilayers with inserting an ultra-thin Co-Fe layer which induces large Mn-XMCD.
物質のフェムト秒物理・化学現象解析のためのX線散乱計測技術

松原英一郎, 西野吉則, 守友浩, 田中義人, 北川進, 高田昌樹, 角田匡清, 中村哲也, 鈴木基寛, 淡路直樹

Offer Organization: 文部科学省

System: Ｘ線自由電子レーザー装置の開発利用

2010 -
非磁性金属と接合した窒化鉄薄膜を用いた高効率スピン源の開発

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 特定領域研究

Institution: 東北大学

2008 - 2009

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最近の理論研究によれば、Fe_4Nはフェルミ準位における状態密度の分極は0.6程度であり、いわゆるハーフメタルではないが、各電子軌道の電気伝導性まで考慮に入れた計算では、伝導率のスピン偏極率は-1となり、高効率のスピン源となることが期待できる。本研究では、Fe_4Nを用いた高効率スピン源の開発を目的として研究を行った。良質なFe_4N薄膜を形成するために、新たに(001)配向したエピタキシャルCu下地膜を開発してFe_4N薄膜を作成した結果、Fe_4Nの結晶品質が格段に向上し、従来の磁気抵抗変化率に比較して3倍以上の性能向上が得られ、室温において最大-75%の負のトンネル磁気抵抗変化率を得た。このことから、トンネル注入法によれば、Fe_4N内の伝導電子の大きなスピン偏極率を保ったままスピン源として機能させることができることが明らかとなった。一方で、非磁性金属(Cu)薄膜と接合したFe_4N/Cu/Fe_4N/MnIrもしくはFe_4N/Cu/CoFe/MmIr型のスピンバルブGMR薄膜を形成し、電子ビーム描画法により微細加工したCPP-GMR素子においては、期待に反して大きな磁気抵抗変化率が得られなかった。このことはFe_4N内部を伝導している高スピン偏極した伝導電子が、非磁性金属(Cu)層にそのスピン偏極率を保ったまま注入されていないことを示唆している。今後、金属伝導型の高効率スピン源としてFe_4N薄膜を機能させるためには、接合する非磁性金属種を変化させ、ヘテロ接合界面においてスピン反転が生じないような材料系を開発する必要があることが明らかとなった。
STUDY FOR MECHANISM OF GIANT EXCHANGE ANISOTROPY AND DEVELOPMENT OF HIGH PERFORMANCE Mn BASED ANTIFERROMAGNETIC MATERIALS

TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2006 - 2007

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The exchange anisotropy is a phenomenon to fix the spins in ferromagnet and utilized in spintronics devices such as magnetic random access memories and spin valve type reproducing head element in ultrahigh density magnetic recording system. The purpose of the present study is to understand the mechanism of exchange anisotropy and to develop the high performance antiferromagnetic materials, through the study of inducing mechanism of giant exchange anisotropy (J_K=1.3 erg/cm^2) that has been discovered by the present authors group. In this research project, following terms have been investigated. 1. Correlation between the microstructure and exchange anisotropy of the exchange biased bilayers. 2. Spin structure and magnetization process of antiferromagnetic layer by soft x-ray magnetic circular dichroism (XMCD). 3. Development of microscopic model for exchange biased bilayers and theoretical calculations. 4. Fabrication and estimation of theoretically designed practical exchange biased bilayers. Main results obtained are summarized as follows. Uncompensated antiferromagnetic spin induced at the interface was quantitatively investigated by XMCD technique. The uncompensated antiferromagnetic spins change their sign and magnitude, as the ferromagnetic Co-Fe layer composition is changed. While, the exchange biasing strength is also changed as a function of the Co-Fe composition, close correlation has been suggested between them. Standing on the above finding, ultra-thin Mn layer insertion at the interface has been designed to enhance the exchange anisotropy and experimentally confirmed the doubling strength of exchange anisotropy. From a dependence of exchange anisotropy on the antiferromagetic layer composition, it is suggested that the inserted Mn layer has 3Q spin structure differently from the bulk Mn, in order to trace the fcc structure of the underlying Mn-Ir layer.
Magnetic Structural Analysis of Magnetic Thin Films Artificially Modulated on a Monatomic Layer scale by Polarized Neutron Scattering Technique

TAKEDA Masayasu, ASAOKA Hidehito, KAKURAI Kazuhisa, TSUNODA Masakiyo, TAKANASHI Koki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Japan Atomic Energy Agency

2005 - 2007

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1. Polarized neutron options for a triple-axis neutron spectrometer, TAS-1, and a neutron reflectometer, SUIREN, have been improved. The spectrometer and reflectometer are installed at research reactor JRR-3 of Japan Atomic Energy Agency (JAEA) and are now capable of the detailed magnetic structural analysis of the thin magnetic films whose scattering volumes are very tiny. 2. Spherical polarization analysis of an artificially confined spin-density wave in Cr/Sn multilayer has been successfully given using combination of TAS-1 and CRYOPAD (CRYOgenic Polarization Analysis Device). CRYOPAD can measure the three components of the polarization of scattered neutrons, and consequently can determine complicated spin structures in antiferromagnetic specimen. 3. Magnetic films synthesized by the investigators and the other collaborators have been investigated using TAS-1 and SUIREN. For example it has been revealed that no giant magnetic moment exists in α"-Fe_<16>N_2 thin films with an optimum nitrization using TAS-1. The giant magnetic moment in α"-Fe_<16>N_2 had been a long term issue. 4. Deposition of Ruthenium (Ru) has been succeeded using the Knudsen Cell with the rate of 0.001nm/sec. at 1985 C. Ru is a key material for improvement of the performance of magnetic recoding read-head. The deposition using K cell had never been tried because of the high melting point of Ru although high-quality epitaxial growth was generally expected using the K cell. We are now going to the next step to synthesize high-quality epitaxial films using the K cell and the van der Waals epitaxy method.
ポリオールプロセスを用いた多目的用均一粒径ナノ粒子合成技術の確立

B Jeyadevan, 角田匡清, 篠田弘造, 佐藤義倫, 田路和幸, 松本高利

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(A)

Institution: 東北大学

2005 - 2007

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本研究における具体的な研究開発要素は、ポリオールプロセスにおけるナノ粒子の化学合成プロセスの機構解明とそれに基づくナノ粒子の組成・構造の精密制御プロセスの確立し、様々な目的にあったナノ粒子の材料設計ならびに単分散ナノ粒子の製造を行うものである。その目的の達成を目指して次の項目について研究を行った。 1.ポリオールプロセスの反応機構解明-X線吸収微細構造測定および紫外可視光吸収分光法を用い、コバルト粒子生成系を対象として本プロセスの反応機構解明を試みた。 2.反応速度の促進-ポリオールプロセスの反応速度の促進あるいは制御が得られる精製物質の物性、たとえば粒子サイズ、結晶構造などの制御に必要不可欠である。したがって、反応速度に影響及ぼす因子であるポリオール類意、金属塩類、反応促進剤などの有効性について検討した。ポリオール類の還元力の評価において分子軌道法および電気化学手法を用いた評価し、有効性を実験的に確認した。また、金属塩類や反応促進剤についても実験的な検討を行った。 3.金属及び合金ナノ粒子の合成-ポリオールプロセスを用いた合成においてはじめて純粋なFe及びFeCoナノ粒子の合成に成功した。また、導電性ナノ粒子合成においても銀および銅ナノ粒子の合成やそれらの酸化安定性に優れた被覆膜形成技術の開発に成功した。 4.金属および合金応用技術開発-20nm以下のFeCo合金微粒子の合成に成功しそれら高周波特性を評価しFeCo微粒子はGHz帯での周波数応答を示し、電磁波吸収体用材料としてのポテンシャルを確認した。また、電極触媒としてのFePt微粒子の活性評価について-本プロセスにより作成したFePt微粒子の燃料電池用アノード触媒としの活性評価を行った結果、Ptと比較して高い耐CO被覆性が確認され、アノード触媒材料としての有用性が示された。
電子ビーム選択CVDによるナノメートル級ハードマスクの作製とパターンニング

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 萌芽研究

Institution: 東北大学

2005 - 2006

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電子伝導に及ぼす磁性の影響は存外に大きく、いわゆるスピンエレクトロニクス分野では、巨大磁気抵抗(GMR)効果、トンネル磁気抵抗(TMR)効果、スピンアキュムレーション、スピントルク磁化反転など、ここ十数年の間に数々の新物理現象の発見が相次いでいる。これらスピンエレクトロニクスの発展には素子サイズの超微細化が重要な役割を果たしており、90年代の薄膜技術の進展による膜厚方向のナノスケール化と、主に今世紀に入って以降の微細加工技術による薄膜面内方向でのサブミクロン化が必要欠くべからざる要素であった。本研究では、面内方向のナノスケール化を実現すべく、電子ビームの極小フォーカス機能を利用した、選択CVD法による面内寸法10nm以下のハードエッチングマスクの形成と、それによる機能性磁性多層薄膜のパターンニングを目指した。本年度は、Al-N層をバリア層にもつTMR膜ならびに膜面垂直通電型(CPP-)GMR膜上に、電子ビーム援用選択CVD法によって形成したW(タングステン)製のナノピラーをマスクとしたイオンミリング法により、極小スピントロニクス素子の形成を行った。その結果、最小寸法径34nmの極小CPP-GMR素子を得た。得られたCPP-GMR素子の磁気抵抗効果を評価した結果、通常のフォトリソグラフィー法により加工した素子と同程度のMR特性を保持していること、ならびに電流誘起磁化反転現象の観測に成功した。また、比較対照として電子線リソグラフィー法によるリング形状のTMR素子加工を行い、その磁化反転過程を明確化した。さらにCPP-GMR素子における電流通電面積の更なる狭小化を目指し、積層膜構造中に1nm程度の通電領域を有する極薄酸化膜(NOL)の形成・評価技術についても検討を行い、島状成長させたAl-O膜により効率的に通電領域の制限が可能であることを明らかとした。
Development of New Magnetic Sensor Utilizing the PMR Effect of Half-Metallic Ferromagnetic Powders

TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: TOHOKU UNIVERSITY

2004 - 2005

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Chromium dioxide (CrO_2) is expected to be a strong spin polarizer in forthcoming spinelectronics devices, since it has been theoretically predicted as a half-metallic material on one hand and nearly perfect spin polarization has been experimentally demonstrated on the other. In cold-pressed CrO_2 powder compacts, large magnetoresistance (MR) that originates due to the intergranular spin dependent tunneling was observed at low temperatures. However, the relatively low Curie temperature of CrO_2 (T_c 〜 400 K) prevents it from being used in device applications. Elevating the Curie temperature of CrO_2 is indispensable factor to realize powder magnetoresistance (PMR) sensors for room temperature application. The present authors have succeeded in synthesizing CrO_2 powders through mechanochemical method, and doping was easily achieved by introducing the dopant as raw material. Thus, in the present study, we investigated the influence of doping elements and their concentration on the magnetic and magnetotransport properties of CrO_2 powder compacts. The (Cr-M)O_2 (M=V,Mn,Fe,Co) powders were synthesized by the mechanochemical method and the magnetoresistance (MR) effect of their powder compacts was investigated as a function of the type and content of the dopant. The findings are summarized below. Substituting limit of M for Cr in CrO_2 was 30 at% for V, Mn, and Co, and 5 at% for Fe. Doping with V effectively decreases the T_c, while Fe significantly elevates the same (420 K with 5 at% Fe). Furthermore, the changes observed in the cases of Co and Mn was marginal. MR ratio was significantly enhanced up to 22% at 4.2 K with the doping of 5 at% of Fe, however, decreased in the cases of V and Co doping. The reason for the MR enhancement in (Cr-Fe)O_2 powder compacts is due to the change in the barrier characteristics.
スピンバルブ型バリスティックMR薄膜の作製

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 萌芽研究

Institution: 東北大学

2003 - 2004

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2つの強磁性体のナノコンタクトで観測されるバリスティック磁気抵抗(BMR)効果を解明・実用化するためには、電子伝導の量子化が発現するナノメートルオーダーの電流の絞込み領域を完全に制御して形成することが最も重要な技術である。本研究の第一目的は、極薄絶縁膜面内へのナノメートルオーダーの導電領域(ナノコンタクトホール:NCH)の均一形成手法を開発し、強磁性層/NCH絶縁層/強磁性層/反強磁性層の基本4層構成からなるスピンバルブ型バリスティックMR薄膜を作製することにある。NCHを有するスピンバルブ素子において、BMR効果を観測するためには、素子面積内にNCHの存在数を1〜数個のオーダーとするために、素子サイズを数十nmのサイズに加工する必要がある。同時に、そのような微細素子においても反磁界に抗して2枚の強磁性層の磁化の平行/反平行配列を確実に制御する必要がある。本年度は数十nmサイズの素子加工を行うためのハードマスクとしての30nm径のC(カーボン)ピラーの成長技術を、電子ビーム援用CVD法によって確立した。また、数十nmサイズのスピンバルブ素子の固定層磁化の固着能力を確保するために、巨大な一方向異方性定数を発現できるMn_3Ir合金を新たな反強磁性層材料として開発した。さらにNCH形成のために、MgO絶縁膜の初期成長過程をconductive AFM法を用いて詳細に検討を行い、膜厚0.8nmを境にMgO膜が二次元連続状に変化するために、強磁性ピンホールが消失することを明らかにした。現時点ではスピンバルブ素子でのBMR効果の観測には至っていないが、本研究成果を統合した数十nmサイズのスピンバルブ型MR素子の実現によって、再現性の高いBMR効果の観測が期待できる。
Development of spin funneling magnetic field sensor devices for high sensitive and high space-resolution magnetic imaging plates

TAKAHASHI Migaku, TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2002 - 2004

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In order to realize a high sensitive and high space-resolution magnetic imaging plate, we investigated fabrication processes of spin tunneling magnetic field sensor devices. With the microwave excited plasma oxidizatioin or nitridation method using radial line slot antenna (RLSA) irradiator, ferromagnetic tunnel junctions (MTJs) in stack of bottom-electrode/Mn-Ir/Co-Fe/barrier/Co-Fe/Ni-Fe/upper-electrode were fabricated on a thermally oxidized Si wafer. The barrier was formed by the plasma oxidization or nitridation process with X+O_2 or X+N_2 (X=He,Ar,Kr) mixed gases, immediately after the deposition of 0.8-1.5 nm-thick metal Al films. In the case of MTJs with Al-O barrier oxidized from 1.5-nm-thick Al film, the maximum TMR ratio was achieved to 58.8%, which was the world record at the time. In the case of MTJs with Al-N barrier nitrided from 1.0-nm-thick Al film, the maximum TMR ratio overcame the conventional record of 33% and reached 49%. It was also found that plasma nitridation of metal Al films progresses more mildly than the plasma oxidization of them. This means that the plasma nitridation is suitable for the formation process of ultra-thin barrier layers. High concentration ozone oxidization process of ultra-thin metal films and magnetotransport properties of MTJs fabricated with this process were also investigated. As results followings were found. The oxidization process of metal films are different between the ozone exposure method and the plasma exposure method. The oxidizing rate (parabolic rate constant, k_p), dominated by the diffusion velocity of oxidizing species in the oxide layer, is smaller by two-orders in magnitude for the ozone process than that for the plasma process, while the thickness of oxide layer, immediately formed on the surface at the very early stage of oxidization, is almost same. This means that the high concentration ozone oxidization method is suitable for the precise control of oxidization of ultra-thin metal films.
GIANT EXCHANGE ANISOTROPY OF FERROMAGNETIC/ANTIFERROMAGNETIC BILAYERS INDUCED BY THE CONTROLE OF THEIR MICROSTRUCTURE AND INTERFACE

TSUNODA Masakiyo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: TOHOKU UNIVERSITY

2002 - 2003

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The exchange anisotropy of pseudo-single crystalline Mn-Ir/Co-Fe bilayers with different crystallographic orientations, such as (110), (001), and (111), was investigated. As results, we found that the unidirectional anisotropy constant, J_K, strongly depends on the crystallographic orientation, while the critical thickness of the AF layer, d_<AF>^<cr>, is similarly 〜 3 nm. As a notable result, the J_K of the (110)-epitaxial bilayer with d_<AF> = 4 nm shows extra large value of 0.73 erg/cm^2. The magnetic anisotropy of the Mn-Ir layer determined from the saturation torque amplitude was 8.5×10^5 erg/cm^3 for (110)-, 5.0×10^4 erg/cm^3 for (001)-, and 10^3 〜 10^4 erg/cm^3 for (111)-bilayer, respectively. From the correlation between the exchange anisotropy and the magnetic anisotropy of the Mn-Ir layer, we conclude that the domain wall model is inadequate to explain these experimental results and the single spin model can do it qualitatively, assuming that the interfacial exchange coupling energy differs in the respective crystallographic orientation. The effect of long-time annealing on the exchange anisotropy of polycrystalline Mn_<75>Ir_<25> d_<AF>/Co_<70>Fe_<30> 4 nm bilayers was also investigated to induce large unidirectional anisotropy constant, J_K, with very thin antiferromagnetic layer. As a notable result, extra large value of J_K = 0.87 erg/cm^2 was obtained in the bilayer with d_<AF> = 5 nm after 200-h-annealing at 250℃, which is larger than the twice of the maximum value of PtMn/Co-Fe system. According to the single spin ensemble model, established by the investigator, the enlargement of J_K by the long-time annealing is explained as a result of the change of the distribution of antiferromagnet spin directions. The magnetic anisotropy energy of Mn-Ir grains was determined as 7×10^3 erg/cm^3 from the activation energy of the enlarging J_K process, experimentally obtained.
磁気トルクロス解析による強磁性/反強磁性積層膜の交換磁気異方性発現機構の解明

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 奨励研究(A)

Institution: 東北大学

1999 - 2000

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スピンバルブ型GMR薄膜に不可欠な界面物理事象の一つである、強磁性層/反強磁性層積層膜の交換磁気異方性は、その発現メカニズムが完全に理解されているとは言いがたい状況にある。1956年の現象の発見以来、定性的なモデルとして用いられてきたMeiklejohnのSingle spin model(SSM)による実験結果の説明は十分でなく、現象理解の大きな壁であった。本研究では、磁気トルクロス解析を中心として、積層膜の微細構造と交換磁気異方性との相関について詳細に検討を行い、交換磁気異方性発現のメカニズム解明を図ることを目的とした。超清浄雰囲気スパッタ法を用いて、反強磁性層厚を変化させたNi-Fe/Mn-Ir積層膜を作製し、その微細構造評価ならびに磁気トルク曲線の印加磁界に対する変化を測定した。X線回折法による構造解析の結果、積層膜構造が設計通りによく制御されていることが判った。積層膜断面像および平面像の電子顕微鏡観察結果からは、積層膜が多結晶構造を有し、膜面に対して強く(111)配向し、膜面内に対してはランダムな配向を有するシートテクスチャであることが判った。磁気トルク曲線の測定結果と、SSMによる計算結果とは、定性的に良く一致するものの、反強磁性層厚が臨界膜厚以下の場合には、高印加磁界下において、回転ヒステリシス損失が、印加磁界依存性を持たず、計算結果との不一致を示した。これは、SSMで仮定している反強磁性層膜全体にわたるマクロな一軸磁気異方性に起因しており、反強磁性粒子の結晶磁気異方性が膜面内にランダムな方向を向いて分散している状態を取り入れたSingle spin ensemble model(SSEM)によって説明が可能であることを明らかとした。SSEMに従えば、磁界中冷却による交換磁気異方性の可逆的方向制御のメカニズムが、薄膜微細構造の変化を伴わずに説明可能であり、経験的に良く知られた実験事実と相容れることが明らかとなった。
DEVELOPMENT OF HIGH SENSITIVE THIN-FILM MAGNETIC SENSORS BY APPLYING THE IMPURITY REDULATED SPUTTERING PROCESS

TSUNODA Masakiyo, UNEYAMA Kazuhiro, TAKAHASHI Migaku

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B).

Institution: TOHOKU UNIVERSITY

1999 - 2000

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The giant magnetoresistance(GMR)effect in metallic multilayer has been actively investigated to be applied to magnetic sensors. Key technical factors to obtain sensitive MR response are 1)flat interfaces of multilayers to retain large MR ratio and 2)soft magnetic properties of ferromagnetic layers, such as Co iud Co-Fe. These two factors are realized with controlling impurities in fabrication process. Introducing oxygen into the sputtering atmosphere during the deposition is an effective way to improve the interfacial flatness, which has been demonstrated for Co/Cu multilayers by the present authors. Nitrogen and boron are well-know additives to make magnetic softering of Co-Fe films. In the present study, in order to clarify the role of oxygen on GMR more precisely, Co/Cu multilayers were fabricated under different sputtering atmospheres in which the impurity oxygen content was changed dramatically from 0.1 ppm to 0.1 % within processing Ar gas. The correlation between the MR ratio and microstructure of the multilayers, especially the interfacial roughess, was investigated as a function of the partial pressure of oxygen introduced into the sputtering chamber. The MR ratio drastically increased from less than 20 % to 54 % when the content of impurity oxygen was slightly increased from 20 ppm to 80 ppm, then nearly varished when the content become more than 200 ppm. In the former region where the MR ratio steeply increased, the root mean square rougtness of the multilayers decreased from 6.5 Å to 4.5 Å accompanied by a reduction of in grain size as the oxygen content was increased. The partial oxidation of the multilayers is the most probable mechanism by which the flattening of the interfaces in the multilayer can be explained.
MICROSTRUCTURAL CONTROL OF THE INTERFACE FOR SPIN-VALVE GMR THIN-FILMS BY APPLYING THE ULTRA CLEAN SPUTTERING PROCESS

TAKAHASHI Migaku, KIRA Tooru, TSUNODA Masakiyo, SHOJI Hiroki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (A)

Institution: TOHOKU UNIVERSITY

1997 - 1999

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The extremely clean sputtering process (XC process) was newly introduced in the fabrication of ultra-thin spin valves to control the microstructure and to establish the excellent magnetic properties. The relation between cleanness during film deposition process and the magnetic properties of spin valve elements has been discussed in connection with their microstructure. Sub./Ta/Ni-Fe/Mn-Ni/Ni-Fe and Sub./Ta/Ni-Fe/Mn-Ir/Ta quadrilayers were fabricated under the different purity of the sputtering atmospheres. Strength of the exchange anisotropy measured at room temperature was enhanced in very thin F/AF bilayer fabricated under the XC-process, comparing with the bilayer fabricated under a lower graded (LG-) process, which only differed in the base pressure of the sputtering chamber : 10ィイD1-7ィエD1 Torr order. From a structural analysis and a temperature dependence of the exchange anisotropy of the bilayers, grains in the bilayers fabricated under the XC-process were found to be enlarged and that the enhancement of exchange anisotropy was caused by the enlargement of antiferromagnetic grains, which suppress thermal agitation and lowering the local blocking temperature. For the electron transport, the enlargement of the grains observed in the XC-processed films also played an important role. The decrease of grain boundaries and impurities in the films, reduced saturated resistivity of the spin valves, Sub. Ta/Ni-Fe/Co/Cu/Co/Mn-Ir/Ta, with lowering the impurity level in the sputtering atmosphere and resulted in the increase of the MR ratios. The MR ratio of tan optimized spin valve fabricated under the XC-process achieved to 9.7%, even in the total thickness of 148 【encircledA】 except for the capping Ta layer, while that of the LG-processed spin valve dropped to 0.9% due to the vanish of the exchange anisotropy. We concluded that the extremely clean sputtering process is greatly effective to realize ultra-thin spin valves and that to avoid rumpling interfaces of them it important to induce the adequate magnetic properties.
NANO STRUCTURE CONTROL OF HETERO-INTERFACE FOR METALLIC MULTILAYERS BY USING NEW FABRICATION TECHNIQUE WITH THE SUBSTRATE EXCITED BY SURFACE ACOUSTIC WAVES

TSUNODA Masakiyo, KOSHIMURA Masaki, SHIBA Takashi, TAKAHASHI Migaku

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Developmental Scientific Research (B)

Institution: TOHOKU UNIVERSITY

1994 - 1995

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The aims of this study is to fabricate the matallic multilayrs of which situations at the interface between the different two metals were optimized in atomic scale, and to develop the sensing devices for magnetic field with high sensitivity, by means of applying the new fabricating technology for thin film with using the substrate excited by surface acoustic waves (SAW). Prior to fabricating multilayrs, the monitoring method for initial growth stage of matallic thin films, which is indispensable for fabricating multilayrs, were developed and worth results were obtained as summarized below. The detailed relations between the strong dumping of SAW and the microstructures of metallic thin films at the initial growth stage were investigated. The mass thickness, at which the SAW amplitude reaches minimum were found to correspond to the critical thickness, at which the film structure changes from island-like to continuous. From the investigation for the influence of metal seed layrs on initial film growth by referring above relations, it was found that islands of the seed layr capture the adatoms diffused over the substrate surface, becom growth centers for the subsequent film deposition, and help to make smooth surface of ultra thin metallic films. The structural changes of ultra thin metallic firms with low melting point like as Ag and Cu were also observed, when depositions were stopped at the initial growth stages. Standing on these results, Co/Cu multilayrs were fabricated on the substrate excited by SAW under various SAW amplitude, and estimated those sensing properties. In the multilayr which was fabricated under small SAW amplitude, the maximum magnetoresistance ratio was observed, and the optimized interfacial structure was realized.
弾性表面波を用いた新成膜技術による面内周期変調構造を有する薄膜の作製

角田匡清

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 奨励研究(A)

Institution: 東北大学

1994 - 1994

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本研究の目的は、報告者らがこれまでに明らかにした、弾性表面波で基板を励振することで金属薄膜の微細構造を制御する成膜技術を用い、面内に定在波を誘起した弾性表面波励振基板を新たに作製し、面内に周期変調構造を有する薄膜の作製を試みることである。これに従って、先ず、進行波用の弾性表面波励振基板(ニオブ酸リチウム単結晶基板)表面の両端に、フォトリソグラフの手法を用いてスパッタリング法でAI反射格子電極を設けた。10mm×16mmの基板上に、有効励振幅6mm、金属薄膜成膜領域幅6.5mmを中央部に確保し、その両端に2.5対のすだれ状励振電極、さらにその外側に格子数100本からなる反射電極を設けた構造の弾性表面波共振子を設計し、シミュレーションにより共振子の周波数特性(通過特性)を確認した。計測器等の問題からインピーダンス50Ω、共振周波数は45MHzとした。次に、この共振子基板上に真空蒸着法を用いて作製した金属薄膜の膜面内周期変調構造を確認するための準備実験として、成膜中の薄膜抵抗のin-situ測定を試みた。パーソナルコンピュタ-で測定制御されたデジタルマルチメータを用いて、直流四端子法で成膜中のAg薄膜の抵抗値の変化を測定するシステムを構築した。成膜開始直後の薄膜のシート抵抗値は200MΩ以上であるが、膜厚およそ80Åから測定可能な200MΩ以下となり、膜厚に対して指数関数的に減少するが、膜厚およそ90Å付近で1MΩから10kΩへの急激な減少が観測され、島状から連続状への薄膜の微細構造の変化が薄膜の抵抗値測定で観測し得ることを明らかにした。今後は、本手法を用いて、定在波による変調方向と、これに対して垂直な方向の薄膜の抵抗値を膜厚の関数として測定し、金属薄膜の膜面内周期変調構造を確認する。

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Social Activities 4

前橋高校出前授業

2011/10/26 -

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放射光で探るハードディスクのナノ磁石
SPring-8 施設公開科学講演会

2009/04/26 -

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放射光で探るハードディスクのナノ磁石
結晶内のばらつき半分

2008/10/15 -

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超高密度ハードディスク（HDD）の再生ヘッド用強磁性トンネル接合素子（MTJ）の材料技術を開発。富士通との共同研究成果。CoFeB/MgO/CoFeB-MTJを超高密度HDDヘッドに応用するためには、MgOトンネル障壁層厚を薄くして、素子抵抗を低減する必要がある。従来、MgO膜厚の低減は、MgOの結晶性の低下を招き、MTJの特性劣化を引き起こしていた。MgOの成膜直後に加熱処理を加えるプロセスを開発することでMgOの結晶性向上を実現し、MTJの低抵抗化に成功した。
HDD容量３倍富士通など磁気ヘッド改良

2007/01/12 -

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超高密度ハードディスク（HDD）用再生ヘッドを改良し記憶容量を３倍に高めることが可能な磁性材料を開発。富士通との共同研究成果。従来再生ヘッドに用いられていた反強磁性材料（不規則合金Mn-Ir）に対して、規則合金Mn3Irを用いることで、磁化固着力を増強。その結果、記録トラックの幅を従来の1/2以下にできた。

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「物質のフェムト秒物理・化学現象解析のためのX線散乱計測技術」（回折磁気スペックル計測用薄膜デバイスの開発）

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Ｘ線自由電子レーザー光源が完成した際に、高強度でパルス性を示す完全なコヒーレンス光源を試料に照射して得られる散乱パターンを使って、誘起される物質中の構造相転移、光誘起、動的磁化などの物理現象や、吸着などの化学現象をフェムト秒時間分解能で観察する計測技術を開発する。
極小デバイス磁化挙動解析のための回折スペックル計測技術の開発

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次世代スピントロニクスデバイスの開発に不可欠な、微小磁性体の静的・動的磁化挙動解析技術として、Ｘ線自由電子レーザーのコヒーレント性を利用した回折スペックル計測による、微小磁性体内の磁化ベクトル分布解析技術を高輝度光科学研究センター、富士通株式会社と共同で確立する。
高機能・超低消費電力メモリの開発

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次世代の高速、高密度と超低消費電力を合わせ持つ不揮発性のスピンメモリを実現するための、種々の克服すべき技術課題に解を与えて産業化への道をつける。
超清浄雰囲気スパッタによる超高密度磁気記録用高感度スピントンネルヘッドの開発

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超清浄雰囲気スパッタによる超高密度磁気記録用高感度スピントンネルヘッドの開発
超清浄スパッタプロセスによる超高密度磁気記録デバイスの創成

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超清浄スパッタプロセスによる超高密度磁気記録デバイスの創成