研究者詳細

顔写真

ドヒ　タカアキ
土肥　昂尭
Takaaki Dohi
所属
電気通信研究所　計算システム基盤研究部門　革新的スピントロニクスデバイス研究室
職名
助教
学位

  • 博士（工学）（東北大学）

  • 修士（工学）（東北大学）

e-Rad 研究者番号
20972376
Researcher ID
T-7994-2019

経歴 4

  • 2024年7月 ～ 継続中
    東北大学　電気通信研究所　助教

  • 2022年8月 ～ 継続中
    東北大学　電気通信研究所　助教

  • 2020年9月 ～ 2022年7月
    Johannes Gutenberg-Universität Mainz　Institute of Physics　Postdoctoral researcher

  • 2020年4月 ～ 2020年8月
    東北大学　電気通信研究所　博士研究員

学歴 3

  • 東北大学　大学院工学研究科　電子工学専攻

    2017年4月 ～ 2020年3月

  • 東北大学　大学院工学研究科　電子工学専攻

    2015年4月 ～ 2017年3月

  • 佐賀大学　理工学部　電気電子工学科

    2013年4月 ～ 2015年3月

所属学協会 1

  • 応用物理学会

    2016年3月 ～ 継続中

研究キーワード 1

  • スピントロニクス

研究分野 1

  • ナノテク・材料 / 応用物性 / スピントロニクス

受賞 7

  1. 船井研究奨励賞

    2025年5月　公益財団法人 船井情報科学振興財団　反強磁性スキルミオニクスの開拓

  2. 令和5年度 東北大学電気・情報系 若手優秀研究賞

    2024年3月　東北大学

  3. 工学研究科長賞

    2020年3月　東北大学

  4. Editors' Highlights

    2019年11月　Nature Communications　Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles

  5. 第46回（2019年春季）応用物理学会 講演奨励賞

    2019年9月　応用物理学会

  6. Featured Article

    2018年5月　Applied Physics Letters　Non-linear variation of domain period under electric field in demagnetized CoFeB/MgO stacks with perpendicular easy axis

  7. 成績優秀賞

    2015年3月　電子情報通信学会九州支部

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論文 18

  1. Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets 査読有り

    Mona Bhukta, Takaaki Dohi, Venkata Krishna Bharadwaj, Ricardo Zarzuela, Maria-Andromachi Syskaki, Michael Foerster, Miguel Angel Niño, Jairo Sinova, Robert Frömter, Mathias Kläui

    Nature Communications　15　(1)　1641-1-1641-10　2024年2月26日

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

    DOI： 10.1038/s41467-024-45375-z 　

    eISSN：2041-1723

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    Abstract The ever-growing demand for device miniaturization and energy efficiency in data storage and computing technology has prompted a shift towards antiferromagnetic topological spin textures as information carriers. This shift is primarily owing to their negligible stray fields, leading to higher possible device density and potentially ultrafast dynamics. We realize in this work such chiral in-plane topological antiferromagnetic spin textures namely merons, antimerons, and bimerons in synthetic antiferromagnets by concurrently engineering the effective perpendicular magnetic anisotropy, the interlayer exchange coupling, and the magnetic compensation ratio. We demonstrate multimodal vector imaging of the three-dimensional Néel order parameter, revealing the topology of those spin textures and a globally well-defined chirality, which is a crucial requirement for controlled current-induced dynamics. Our analysis reveals that the interplay between interlayer exchange and interlayer magnetic dipolar interactions plays a key role to significantly reduce the critical strength of the Dzyaloshinskii-Moriya interaction required to stabilize topological spin textures, such as antiferromagnetic merons, in synthetic antiferromagnets, making them a promising platform for next-generation spintronics applications.

  2. Magneto-ionic modulation of the interlayer exchange interaction in synthetic antiferromagnets 査読有り

    Maria-Andromachi Syskaki, Takaaki Dohi, Beatrice Bednarz, Sergei Olegovich Filnov, Sergey Alexeyevich Kasatikov, Mona Bhukta, Alevtina Smekhova, Rohit Pachat, Johannes Wilhelmus van der Jagt, Shimpei Ono, Dafiné Ravelosona, Jürgen Langer, Mathias Kläui, Liza Herrera Diez, Gerhard Jakob

    Applied Physics Letters　124　(8)　082408-1-082408-7　2024年2月19日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/5.0198750 　

    ISSN：0003-6951

    eISSN：1077-3118

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    The electric-field control of magnetism is a highly promising and potentially effective approach for realizing energy-efficient applications. Recent interest has focused on the magneto-ionic effect in synthetic antiferromagnets, driven by its potential to enable high-density data storage devices with ultra-low power consumption. However, the underlying mechanism responsible for the magneto-ionic effect on the interlayer exchange coupling remains elusive. In our work, we find that the modulation of the interlayer exchange coupling is highly sensitive to the thickness of the ferromagnetic layer. We have identified that the changes in the interlayer exchange coupling induced by the gate voltage can be associated with the magneto-ionic effects on the top ferromagnetic layer of the synthetic antiferromagnet. The direct contact between the high ion mobility oxide and the top ferromagnetic layer plays a crucial role in facilitating these effects, largely modifying the anisotropy of the layers. Our findings highlight the important role of magneto-ionic control over the properties of the top ferromagnetic layer in governing the observed modifications in the interlayer exchange coupling. This study provides crucial insight into the intricate interplay between stack structure and magneto-ionic effect on magnetic properties in synthetic antiferromagnetic thin film systems.

  3. Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force 査読有り

    Takaaki Dohi, Markus Weißenhofer, Nico Kerber, Fabian Kammerbauer, Yuqing Ge, Klaus Raab, Jakub Zázvorka, Maria-Andromachi Syskaki, Aga Shahee, Moritz Ruhwedel, Tobias Böttcher, Philipp Pirro, Gerhard Jakob, Ulrich Nowak, Mathias Kläui

    Nature Communications　14　(5424)　1-10　2023年9月11日

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

    DOI： 10.1038/s41467-023-40720-0 　

    eISSN：2041-1723

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    Abstract Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing.

  4. Current-induced magnetization switching in magnetic multilayers with interlayer exchange coupling by dual spin-orbit torque

    Hiroto Masuda, Yuta Yamane, Takeshi Seki, Klaus Raab, Takaaki Dohi, Rajkumar Modak, Ken-ichi Uchida, Jun’ichi Ieda, Mathias Kläui, Koki Takanashi

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

    出版者・発行元： IEEE

    DOI： 10.1109/intermagshortpapers58606.2023.10228598 　

  5. Magnetization switching process by dual spin–orbit torque in interlayer exchange-coupled systems 査読有り

    Hiroto Masuda, Yuta Yamane, Takeshi Seki, Klaus Raab, Takaaki Dohi, Rajkumar Modak, Ken-ichi Uchida, Jun'ichi Ieda, Mathias Kläui, Koki Takanashi

    Applied Physics Letters　122　(16)　162402-162402　2023年4月17日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/5.0140328 　

    ISSN：0003-6951

    eISSN：1077-3118

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    We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses ( tIr), where the perpendicularly magnetized Co layers are coupled ferromagnetically or antiferromagnetically through an interlayer exchange coupling and are sandwiched by the Pt spin Hall layers. The domain structures formed during switching vary depending on the magnetization alignment, i.e., a ferromagnetically coupled or antiferromagnetically coupled configuration. These results clarify the macroscopic picture of switching process for interlayer exchange-coupled systems. The local picture of the switching process is also examined by a numerical calculation based on a macrospin model, which reveals the switching dynamics triggered by dual spin–orbit torques for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin–orbit torques from the two Pt layers effectively act on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the understanding of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin–orbit torque switching.

  6. Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion 査読有り

    Yuqing Ge, Jan Rothörl, Maarten A. Brems, Nico Kerber, Raphael Gruber, Takaaki Dohi, Mathias Kläui, Peter Virnau

    Communications Physics　6　(30)　1-6　2023年2月3日

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

    DOI： 10.1038/s42005-023-01145-9 　

    eISSN：2399-3650

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    Abstract In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations.

  7. Brownian reservoir computing realized using geometrically confined skyrmion dynamics 査読有り

    Klaus Raab, Maarten A. Brems, Grischa Beneke, Takaaki Dohi, Jan Rothörl, Fabian Kammerbauer, Johan H. Mentink, Mathias Kläui

    Nature Communications　13　(6982)　1-6　2022年11月15日

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

    DOI： 10.1038/s41467-022-34309-2 　

    eISSN：2041-1723

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    Abstract Reservoir computing (RC) has been considered as one of the key computational principles beyond von-Neumann computing. Magnetic skyrmions, topological particle-like spin textures in magnetic films are particularly promising for implementing RC, since they respond strongly nonlinearly to external stimuli and feature inherent multiscale dynamics. However, despite several theoretical proposals that exist for skyrmion reservoir computing, experimental realizations have been elusive until now. Here, we propose and experimentally demonstrate a conceptually new approach to skyrmion RC that leverages the thermally activated diffusive motion of skyrmions. By confining the electrically gated and thermal skyrmion motion, we find that already a single skyrmion in a confined geometry suffices to realize nonlinearly separable functions, which we demonstrate for the XOR gate along with all other Boolean logic gate operations. Besides this universality, the reservoir computing concept ensures low training costs and ultra-low power operation with current densities orders of magnitude smaller than those used in existing spintronic reservoir computing demonstrations. Our proposed concept is robust against device imperfections and can be readily extended by linking multiple confined geometries and/or by including more skyrmions in the reservoir, suggesting high potential for scalable and low-energy reservoir computing.

  8. Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium 査読有り

    Jonathan Gibbons, Takaaki Dohi, Vivek P. Amin, Fei Xue, Haowen Ren, Jun-Wen Xu, Hanu Arava, Soho Shim, Hilal Saglam, Yuzi Liu, John E. Pearson, Nadya Mason, Amanda K. Petford-Long, Paul M. Haney, Mark D. Stiles, Eric E. Fullerton, Andrew D. Kent, Shunsuke Fukami, Axel Hoffmann

    Physical Review Applied　18　(2)　1-12　2022年8月29日

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

    DOI： 10.1103/physrevapplied.18.024075 　

    eISSN：2331-7019

  9. Skyrmion pinning energetics in thin film systems 査読有り

    Raphael Gruber, Jakub Zázvorka, Maarten A. Brems, Davi R. Rodrigues, Takaaki Dohi, Nico Kerber, Boris Seng, Mehran Vafaee, Karin Everschor-Sitte, Peter Virnau, Mathias Kläui

    Nature Communications　13　(3144)　1-9　2022年6月6日

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

    DOI： 10.1038/s41467-022-30743-4 　

    eISSN：2041-1723

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    Abstract A key issue for skyrmion dynamics and devices are pinning effects present in real systems. While posing a challenge for the realization of conventional skyrmionics devices, exploiting pinning effects can enable non-conventional computing approaches if the details of the pinning in real samples are quantified and understood. We demonstrate that using thermal skyrmion dynamics, we can characterize the pinning of a sample and we ascertain the spatially resolved energy landscape. To understand the mechanism of the pinning, we probe the strong skyrmion size and shape dependence of the pinning. Magnetic microscopy imaging demonstrates that in contrast to findings in previous investigations, for large skyrmions the pinning originates at the skyrmion boundary and not at its core. The boundary pinning is strongly influenced by the very complex pinning energy landscape that goes beyond the conventional effective rigid quasi-particle description. This gives rise to complex skyrmion shape distortions and allows for dynamic switching of pinning sites and flexible tuning of the pinning.

  10. Thin Film Skyrmionics 招待有り 査読有り

    Takaaki Dohi, Robert M. Reeve, Mathias Kläui

    Annual Review of Condensed Matter Physics　13　(1)　73-95　2022年3月10日

    出版者・発行元： Annual Reviews

    DOI： 10.1146/annurev-conmatphys-031620-110344 　

    ISSN：1947-5454

    eISSN：1947-5462

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    In condensed matter physics, magnetic skyrmions, topologically stabilized magnetic solitons, have been discovered in various materials systems, which has intrigued the community in terms of not only fundamental physics but also with respect to engineering applications. In particular, skyrmions in thin films are easily manipulable by electrical means even at room temperature. Concomitantly, a variety of possible applications have been proposed and proof-of-concept devices have been demonstrated. Recently, the field of skyrmion-based electronics has been referred to as skyrmionics and this field has been rapidly growing and extended in multiple directions. This review provides recent progress for skyrmion research in thin film systems and we discuss promising new directions, which will further invigorate the field.

  11. Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks 査読有り

    A.K. Dhiman, T. Dohi, W. Dobrogowski, Z. Kurant, I. Sveklo, S. Fukami, H. Ohno, A. Maziewski

    Journal of Magnetism and Magnetic Materials　529　167699-167699　2021年7月1日

    出版者・発行元： Elsevier BV

    DOI： 10.1016/j.jmmm.2020.167699 　

    ISSN：0304-8853

  12. Influence of domain wall anisotropy on the current-induced hysteresis loop shift for quantification of the Dzyaloshinskii-Moriya interaction 査読有り

    Takaaki Dohi, Shunsuke Fukami, Hideo Ohno

    Physical Review B　103　(21)　1-9　2021年6月29日

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

    DOI： 10.1103/physrevb.103.214450 　

    ISSN：2469-9950

    eISSN：2469-9969

  13. Probing edge condition of nanoscale CoFeB/MgO magnetic tunnel junctions by spin-wave resonance 査読有り

    M. Shinozaki, T. Dohi, J. Igarashi, J. Llandro, S. Fukami, H. Sato, H. Ohno

    Applied Physics Letters　117　(20)　202404-202404　2020年11月16日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/5.0020591 　

    ISSN：0003-6951

    eISSN：1077-3118

  14. Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles 査読有り

    Takaaki Dohi, Samik DuttaGupta, Shunsuke Fukami, Hideo Ohno

    Nature Communications　10　(5153)　1-6　2019年11月14日

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

    DOI： 10.1038/s41467-019-13182-6 　

    eISSN：2041-1723

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    Abstract Skyrmion, a topologically-protected soliton, is known to emerge via electron spin in various magnetic materials. The magnetic skyrmion can be driven by low current density and has a potential to be stabilized in nanoscale, offering new directions of spintronics. However, there remain some fundamental issues in widely-studied ferromagnetic systems, which include a difficulty to realize stable ultrasmall skyrmions at room temperature, presence of the skyrmion Hall effect, and limitation of velocity owing to the topological charge. Here we show skyrmion bubbles in a synthetic antiferromagnetic coupled multilayer that are free from the above issues. Additive Dzyaloshinskii-Moriya interaction and spin-orbit torque (SOT) of the tailored stack allow stable skyrmion bubbles at room temperature, significantly smaller threshold current density or higher speed for motion, and negligible skyrmion Hall effect, with a potential to be scaled down to nanometer dimensions. The results offer a promising pathway toward nanoscale and energy-efficient skyrmion-based devices.

  15. Reversal of domain wall chirality with ferromagnet thickness in W/(Co)FeB/MgO systems 査読有り

    Takaaki Dohi, Samik DuttaGupta, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters　114　(4)　042405-042405　2019年1月28日

    DOI： 10.1063/1.5084095 　

    ISSN：0003-6951

    eISSN：1077-3118

  16. Non-linear variation of domain period under electric field in demagnetized CoFeB/MgO stacks with perpendicular easy axis 査読有り

    N. Ichikawa, T. Dohi, A. Okada, H. Sato, S. Fukami, H. Ohno

    Applied Physics Letters　112　(20)　202402-202402　2018年5月14日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/1.5035487 　

    ISSN：0003-6951

    eISSN：1077-3118

  17. Electric-field effect on spin-wave resonance in a nanoscale CoFeB/MgO magnetic tunnel junction 査読有り

    T. Dohi, S. Kanai, F. Matsukura, H. Ohno

    Applied Physics Letters　111　(7)　072403-072403　2017年8月14日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/1.4999312 　

    ISSN：0003-6951

    eISSN：1077-3118

  18. Effect of electric-field modulation of magnetic parameters on domain structure in MgO/CoFeB 査読有り

    T. Dohi, S. Kanai, A. Okada, F. Matsukura, H. Ohno

    AIP Advances　6　(7)　075017-075017　2016年7月22日

    出版者・発行元： AIP Publishing

    DOI： 10.1063/1.4959905 　

    eISSN：2158-3226

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MISC 1

  1. 人工反強磁性体におけるスキルミオン形成とダイナミクス 招待有り 査読有り

    土肥 昂尭

    まぐね　18　(5)　217-222　2023年10月

共同研究・競争的資金等の研究課題 9

  1. コヒーレントスピンダイナミクスを用いた省エネ・創エネデバイス

    深見 俊輔, Johan Åkerman, 金井 駿, 土肥 昂尭, 竹内 祐太朗, 家田 淳一, 山根 結太

    提供機関：Japan Society for the Promotion of Science (JSPS)

    制度名：KAKENHI

    研究種目：Grant-in-Aid for Scientific Research (S)

    研究機関：Tohoku University

    2024年4月 ～ 2029年3月

  2. キラリティエンジニアリングによる三次元トポロジカル磁気構造ー電気的制御の新展開ー

    土肥 昂尭, Ahmad A. Awad, 丸井 幸博

    提供機関：Japan Society for the Promotion of Science (JSPS)

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Scientific Research (B)

    研究機関：Tohoku University

    2025年4月 ～ 2028年3月

  3. ナノ領域での電力制御に向けた創発受動素子の開拓

    家田 淳一, 荒木 康文, 佐藤 奈々, 土肥 昂尭

    提供機関：Japan Society for the Promotion of Science

    制度名：KAKENHI

    研究種目：Grant-in-Aid for Scientific Research (A)

    研究機関：Japan Atomic Energy Agency

    2024年4月 ～ 2027年3月

  4. スピンホールナノオッシレータのアレイ化による狭線幅RF磁場の生成と応用

    金井 駿, 土肥 昂尭, 石原 淳

    提供機関：Japan Society for the Promotion of Science (JSPS)

    制度名：KAKENHI

    研究種目：Fund for the Promotion of Joint International Research (International Collaborative Research)

    研究機関：Tohoku University

    2023年9月 ～ 2027年3月

  5. 反強磁性トポロジカル磁気構造の電気的検出

    土肥 昂尭

    提供機関：CASIO SCIENCE PROMOTION FOUNDATION

    2024年12月 ～ 2025年12月

  6. 多層薄膜構造における強磁性/反強磁性トポロジカル磁気構造とダイナミクス及び創発現象の開拓

    土肥 昂尭, 山根 結太, Mathias Kläui

    提供機関：Center for Science and Innovation in Spintronics (CSIS), Tohoku University

    制度名：Cooperative Research Project via Cross Appointment with Overseas Researcher

    研究機関：Research Institute of Electrical Communication (RIEC), Tohoku University

    2024年8月 ～ 2025年3月

  7. 多層薄膜構造を用いた未開拓反強磁性トポロジカル磁気構造の実現と機能性開拓

    土肥 昂尭

    提供機関：Japan Society for the Promotion of Science (JSPS)

    制度名：KAKENHI

    研究種目：Grant-in-Aid for Early-Career Scientists

    研究機関：Tohoku University

    2023年4月 ～ 2025年3月

  8. 多層薄膜構造における三次元トポロジカルスピン構造に起因する創発現象の開拓

    土肥 昂尭, 山根 結太, Mathias Kläui

    提供機関：Center for Science and Innovation in Spintronics (CSIS), Tohoku University

    制度名：Cooperative Research Project via Cross Appointment with Overseas Researcher

    研究機関：Research Institute of Electrical Communication (RIEC), Tohoku University

    2023年8月 ～ 2024年3月

  9. Antiferromagnetic skyrmionics- a path to non-conventional computing

    Takaaki Dohi

    提供機関：The Canon Foundation in Europe

    制度名：Research Fellowships

    研究機関：Institute of Physics, Johannes Gutenberg-University Mainz

    2021年9月 ～ 2022年8月

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