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Takaaki Dohi

Section

Research Institute of Electrical Communication

Job title

Assistant Professor

Degree

博士（工学）（東北大学）
修士（工学）（東北大学）

researchmap

https://researchmap.jp/tdohi

J-GLOBAL ID

202201004846258910

e-Rad No.

20972376

ORCID

https://orcid.org/0000-0003-1628-0097

Researcher ID

T-7994-2019

Research History 4

2024/07 - Present

Tohoku University　Research Institute of Electrical Communication　Assistant Professor
2022/08 - Present

Tohoku University　Research Institute of Electrical Communication　Assistant Professor
2020/09 - 2022/07

Johannes Gutenberg-Universität Mainz　Institute of Physics　Postdoctoral researcher
2020/04 - 2020/08

Tohoku University　Research Institute of Electrical Communication　Postdoctoral researcher

Education 3

Tohoku University　Graduate School of Engineering　Department of Electronic Engineering

2017/04 - 2020/03
Tohoku University　Graduate School of Engineering　Department of Electronic Engineering

2015/04 - 2017/03
Saga University　Faculty of Science and Engineering　Electrical and Electronic Engineering

2013/04 - 2015/03

Professional Memberships 1

The Japan Society of Applied Physics

2016/03 - Present

Research Interests 1

Spintronics

Research Areas 1

Nanotechnology/Materials / Applied materials / Spintronics

Awards 7

Funai Information Technology Award for Young Researchers

2025/05　The Funai Foundation for Information Technology　Pioneering antiferromagnetic skyrmionics
令和5年度東北大学電気・情報系若手優秀研究賞

2024/03　東北大学
工学研究科長賞

2020/03　東北大学
Editors' Highlights

2019/11　Nature Communications　Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles
Young Scientist Presentation award

2019/09　Ferromagnetic layer thickness dependent domain wall chirality and sign of effective Dzyaloshinskii-Moriya field in W/(Co)FeB/MgO systems
Featured Article

2018/05　Applied Physics Letters　Non-linear variation of domain period under electric field in demagnetized CoFeB/MgO stacks with perpendicular easy axis
成績優秀賞

2015/03　電子情報通信学会九州支部

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Papers 18

Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets Peer-reviewed

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　2024/02/26
Publisher: 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.
Magneto-ionic modulation of the interlayer exchange interaction in synthetic antiferromagnets Peer-reviewed

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　2024/02/19
Publisher: 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.
Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force Peer-reviewed

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　2023/09/11
Publisher: 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.
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)　2023/05
Publisher: IEEE
DOI： 10.1109/intermagshortpapers58606.2023.10228598 　
Magnetization switching process by dual spin–orbit torque in interlayer exchange-coupled systems Peer-reviewed

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　2023/04/17
Publisher: 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 ( t_Ir), 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.
Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion Peer-reviewed

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

Communications Physics　6　(30)　1-6　2023/02/03
Publisher: 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.
Brownian reservoir computing realized using geometrically confined skyrmion dynamics Peer-reviewed

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

Nature Communications　13　(6982)　1-6　2022/11/15
Publisher: 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.
Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium Peer-reviewed

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　2022/08/29
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevapplied.18.024075 　

eISSN： 2331-7019
Skyrmion pinning energetics in thin film systems Peer-reviewed

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　2022/06/06
Publisher: 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.
Thin Film Skyrmionics Invited Peer-reviewed

Takaaki Dohi, Robert M. Reeve, Mathias Kläui

Annual Review of Condensed Matter Physics　13　(1)　73-95　2022/03/10
Publisher: 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.
Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks Peer-reviewed

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　2021/07/01
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2020.167699 　

ISSN： 0304-8853
Influence of domain wall anisotropy on the current-induced hysteresis loop shift for quantification of the Dzyaloshinskii-Moriya interaction Peer-reviewed

Takaaki Dohi, Shunsuke Fukami, Hideo Ohno

Physical Review B　103　(21)　1-9　2021/06/29
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.103.214450 　

ISSN： 2469-9950

eISSN： 2469-9969
Probing edge condition of nanoscale CoFeB/MgO magnetic tunnel junctions by spin-wave resonance Peer-reviewed

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

Applied Physics Letters　117　(20)　202404-202404　2020/11/16
Publisher: AIP Publishing
DOI： 10.1063/5.0020591 　

ISSN： 0003-6951

eISSN： 1077-3118
Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles Peer-reviewed

Takaaki Dohi, Samik DuttaGupta, Shunsuke Fukami, Hideo Ohno

Nature Communications　10　(5153)　1-6　2019/11/14
Publisher: 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.
Reversal of domain wall chirality with ferromagnet thickness in W/(Co)FeB/MgO systems Peer-reviewed

Takaaki Dohi, Samik DuttaGupta, Shunsuke Fukami, Hideo Ohno

Applied Physics Letters　114　(4)　042405-042405　2019/01/28

DOI： 10.1063/1.5084095 　

ISSN： 0003-6951

eISSN： 1077-3118
Non-linear variation of domain period under electric field in demagnetized CoFeB/MgO stacks with perpendicular easy axis Peer-reviewed

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

Applied Physics Letters　112　(20)　202402-202402　2018/05/14
Publisher: AIP Publishing
DOI： 10.1063/1.5035487 　

ISSN： 0003-6951

eISSN： 1077-3118
Electric-field effect on spin-wave resonance in a nanoscale CoFeB/MgO magnetic tunnel junction Peer-reviewed

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

Applied Physics Letters　111　(7)　072403-072403　2017/08/14
Publisher: AIP Publishing
DOI： 10.1063/1.4999312 　

ISSN： 0003-6951

eISSN： 1077-3118
Effect of electric-field modulation of magnetic parameters on domain structure in MgO/CoFeB Peer-reviewed

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

AIP Advances　6　(7)　075017-075017　2016/07/22
Publisher: AIP Publishing
DOI： 10.1063/1.4959905 　

eISSN： 2158-3226

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Misc. 1

Formation and Dynamics of Antiferromagnetically Coupled Skyrmions in Synthetic Antiferromagnetic System Invited Peer-reviewed

Takaaki Dohi

MAGNETICS JAPAN　18　(5)　217-222　2023/10

Research Projects 9

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

Shunsuke Fukami, Johan Åkerman, Shun Kanai, Takaaki Dohi, Yutaro Takeuchi, Jun'ichi Ieda, Yuta Yamane

Offer Organization: Japan Society for the Promotion of Science (JSPS)

System: KAKENHI

Category: Grant-in-Aid for Scientific Research (S)

Institution: Tohoku University

2024/04 - 2029/03
Three-dimensional topological spin textures by chirality engineering - A new paradigm in electrical control -

Takaaki Dohi, Ahmad A. Awad, Yukihiro Marui

Offer Organization: Japan Society for the Promotion of Science (JSPS)

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2025/04 - 2028/03
Developing emergent passive elements for power control in nanodomain

Jun'ichi Ieda, Yasufumi Araki, Nana Sato, Takaaki Dohi

Offer Organization: Japan Society for the Promotion of Science

System: KAKENHI

Category: Grant-in-Aid for Scientific Research (A)

Institution: Japan Atomic Energy Agency

2024/04 - 2027/03
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

Shun Kanai, Takaaki Dohi, Jun Ishihara

Offer Organization: Japan Society for the Promotion of Science (JSPS)

System: KAKENHI

Category: Fund for the Promotion of Joint International Research (International Collaborative Research)

Institution: Tohoku University

2023/09 - 2027/03
Electrical Detection of Antiferromagnetic Topological Spin Textures

Takaaki Dohi

Offer Organization: CASIO SCIENCE PROMOTION FOUNDATION

2024/12 - 2025/12
Ferro/Antiferromagnetic Topological Spin Textures, Dynamics, and Emergent Phenomena in multilayer systems

Takaaki Dohi, Yuta Yamane, Mathias Kläui

Offer Organization: Center for Science and Innovation in Spintronics (CSIS), Tohoku University

System: Cooperative Research Project via Cross Appointment with Overseas Researcher

Institution: Research Institute of Electrical Communication (RIEC), Tohoku University

2024/08 - 2025/03
Novel antiferromagnetic topological spin structures using thin-film multilayer systems and their functionalities

Takaaki Dohi

Offer Organization: Japan Society for the Promotion of Science (JSPS)

System: KAKENHI

Category: Grant-in-Aid for Early-Career Scientists

Institution: Tohoku University

2023/04 - 2025/03
Emergent phenomena for 3D topological spin structures in thin film multilayer systems

Takaaki Dohi, Yuta Yamane, Mathias Kläui

Offer Organization: Center for Science and Innovation in Spintronics (CSIS), Tohoku University

System: Cooperative Research Project via Cross Appointment with Overseas Researcher

Institution: Research Institute of Electrical Communication (RIEC), Tohoku University

2023/08 - 2024/03
Antiferromagnetic skyrmionics- a path to non-conventional computing

Takaaki Dohi

Offer Organization: The Canon Foundation in Europe

System: Research Fellowships

Institution: Institute of Physics, Johannes Gutenberg-University Mainz

2021/09 - 2022/08

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