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論文

Magnetization switching process by dual spin-orbit torque in interlayer exchange-coupled systems

増田 啓人*; 山根 結太*; 関 剛斎*; Raab, K.*; 土肥 昂尭*; Modak, R.*; 内田 健一*; 家田 淳一; Kl$"a$ui, M.*; 高梨 弘毅

Applied Physics Letters, 122(16), p.162402_1 - 162402_7, 2023/04

 被引用回数:0 パーセンタイル:59.51(Physics, Applied)

We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses ($$t_mathrm{Ir}$$), 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., 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 torque for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin-orbit torque from the two Pt layers effectively acts on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the under- standing of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin-orbit torque switching.

論文

Thermal stability of non-collinear antiferromagnetic Mn$$_3$$Sn nanodot

佐藤 佑磨*; 竹内 祐太郎*; 山根 結太*; Yoon, J.-Y.*; 金井 駿*; 家田 淳一; 大野 英男*; 深見 俊輔*

Applied Physics Letters, 122(12), p.122404_1 - 122404_5, 2023/03

 被引用回数:0 パーセンタイル:59.51(Physics, Applied)

$$D0_{19}$$-Mn$$_3$$Sn, an antiferromagnet having a non-collinear spin structure in a kagome lattice, has attracted great attention owing to various intriguing properties such as large anomalous Hall effect. Stability of magnetic state against thermal fluctuation, characterized in general by the thermal stability factor $$Delta$$, has been well studied in ferromagnetic systems but not for antiferromagnets. Here we study $$Delta$$ of the antiferromagnetic Mn$$_3$$Sn nanodots as a function of their diameter $$D$$. To obtain $$Delta$$, we measure the switching probability as a function of pulse-field amplitude and analyze the results based on a model developed by accounting for two and six-fold magnetic anisotropies in the kagome plane. We observe no significant change in $$Delta$$ down to $$D = 300$$ nm below which it decreases with $$D$$. The obtained $$D$$ dependence is well explained by a single-domain and nucleation-mediated reversal models. These findings provide a basis to understand the thermal fluctuation and reversal mechanism of antiferromagnets for device application.

論文

Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in-plane magnetic field

増田 啓人*; 関 剛斎*; 山根 結太*; Modak, R.*; 内田 健一*; 家田 淳一; Lau, Y.-C.*; 深見 俊輔*; 高梨 弘毅

Physical Review Applied (Internet), 17(5), p.054036_1 - 054036_9, 2022/05

 被引用回数:3 パーセンタイル:69.66(Physics, Applied)

反対称層間交換結合(AIEC)が最近発見され、人工反強磁性体(SAF)の傾角磁化の誘起を通じた磁化スイッチングにおいて極めて重要な役割を果たしている。本研究では、くさび形の層を持つ垂直磁化多層膜Pt/Co/Ir/Co/Ptにおける大きなAIECを報告をする。AIECの有効磁場は、対称的な層間交換結合に関連しており、AIECを強化するための指針を提供する。SAFに対する拡張Stoner-Wohlfarthモデルを開発し、その磁化スイッチングの重要な要素を明らかにする。理論的知識と実験結果を組み合わせることで、面内磁場のみによる垂直磁化スイッチングが達成される。

論文

Observation of domain structure in non-collinear antiferromagnetic Mn$$_3$$Sn thin films by magneto-optical Kerr effect

内村 友宏*; Yoon, J.-Y.*; 佐藤 佑磨*; 竹内 祐太郎*; 金井 駿*; 武智 涼太*; 岸 桂輔*; 山根 結太*; DuttaGupta, S.*; 家田 淳一; et al.

Applied Physics Letters, 120(17), p.172405_1 - 172405_5, 2022/04

 被引用回数:8 パーセンタイル:85.34(Physics, Applied)

We perform a hysteresis-loop measurement and domain imaging for $$(1100)$$-oriented $$D0_{19}$$-Mn$$_{3+x}$$Sn$$_{1-x}$$ $$(-0.11 le x le 0.14)$$ thin films using magneto-optical Kerr effect (MOKE) and compare it with the anomalous Hall effect (AHE) measurement. We obtain a large Kerr rotation angle of 10 mdeg., comparable with bulk single-crystal Mn$$_3$$Sn. The composition $$x$$ dependence of AHE and MOKE shows a similar trend, suggesting the same origin, i.e., the non-vanishing Berry curvature in the momentum space. Magnetic domain observation at the saturated state shows that x dependence of AHE and MOKE is explained by an amount of reversible area that crucially depends on the crystalline structure of the film. Furthermore, in-depth observation of the reversal process reveals that the reversal starts with nucleation of sub-micrometer-scale domains dispersed in the film, followed by a domain expansion, where the domain wall preferentially propagates along the $$[11bar{2}0]$$ direction. Our study provides a basic understanding of the spatial evolution of the reversal of chiral-spin structure in non-collinear antiferromagnetic thin films.

論文

Theory of Emergent Inductance with Spin-Orbit Coupling Effects

山根 結太*; 深見 俊輔*; 家田 淳一

Physical Review Letters, 128(14), p.147201_1 - 147201_6, 2022/04

 被引用回数:3 パーセンタイル:61.09(Physics, Multidisciplinary)

らせん磁性体で最近発見された創発インダクタンスの理論を、空間反転対称性が破れた場合に生じるスピン軌道相互作用を考慮に入れることで任意の磁気テクスチャに拡張する。強磁性体中電子の動的アハロノフ-キャッシャー位相に基づく定式化で、スピン軌道創発インダクタンスの新概念提案を行う。スピン軌道創発インダクタンスは、空間的に一様な磁化でも磁性とスピン軌道相互作用の共存で普遍的に生じ、広範囲の温度と周波数で安定した動作を実現する。空間反転非対称性を備えた強磁性体を含む広く研究されている実験系を、本研究が提供する新しい視点で再考することで、超広帯域周波数範囲でのスピン軌道物理学とスピントロニクスベースの電力管理の研究に新しいパラダイムを開くことにつながる。

論文

Chiral-spin rotation of non-collinear antiferromagnet by spin-orbit torque

竹内 祐太郎*; 山根 結太*; Yoon, J.-Y.*; 伊藤 隆一*; 陣内 佛霖*; 金井 駿*; 家田 淳一; 深見 俊輔*; 大野 英男*

Nature Materials, 20(10), p.1364 - 1370, 2021/10

 被引用回数:62 パーセンタイル:98.73(Chemistry, Physical)

Electrical manipulation of magnetic materials by current-induced spin torque constitutes the basis of spintronics. Recent studies have demonstrated electrical controls of ferromagnets and collinear antiferromagnets by spin-orbit torque (SOT). Here we show an unconventional response to SOT of a non-collinear antiferromagnet, which has recently attracted great attention owing to large anomalous Hall effect despite vanishingly small net magnetization. In heterostructures with epitaxial non-collinear antiferromagnet Mn$$_3$$Sn, we observe a characteristic fluctuation of Hall resistance, which is attributed to a persistent rotation of chiral-spin structure of Mn$$_3$$Sn driven by SOT. We find that level of the fluctuation that varies with sample size represents the number of magnetic domains of Mn$$_{3}$$Sn. In addition, Mn$$_3$$Sn thickness dependence of critical current reveals that SOT generated by small current density below 20 MA cm$$^{-2}$$ effectively acts on the chiral-spin structure even in thick Mn$$_3$$Sn above 20 nm. The results provide unprecedented pathways of electrical manipulation of magnetic materials, offering new-concept spintronics devices with unconventional functionalities and low-power consumption.

論文

Correlation of anomalous Hall effect with structural parameters and magnetic ordering in Mn$$_{3+x}$$Sn$$_{1-x}$$ thin films

Yoon, J.-Y.*; 竹内 祐太郎*; DuttaGupta, S.*; 山根 結太*; 金井 駿*; 家田 淳一; 大野 英男*; 深見 俊輔*

AIP Advances (Internet), 11(6), p.065318_1 - 065318_6, 2021/06

 被引用回数:12 パーセンタイル:80.58(Nanoscience & Nanotechnology)

We investigate the relationship between structural parameters, magnetic ordering, and the anomalous Hall effect (AHE) of Mn$$_{3+x}$$Sn$$_{1-x}$$ ($$-0.42 le x le +0.23$$) thin films annealed at various temperature $$T_a$$. The crystal structure changes with $$x$$ and $$T_a$$ and at $$T_a ge 500$$ $$^circ$$C near the stoichiometric composition ($$-0.08 le x le +0.04$$) epitaxial single-phase $$D$$0$$_{19}$$-Mn$$_{3+x}$$Sn$$_{1-x}$$($$10bar{1}0$$) is obtained. At room temperature, a larger AHE is obtained when the single-phase epitaxial Mn$$_3$$Sn with the lattice constant closer to that of bulk is formed. The temperature dependence of the AHE shows different behaviors depending on $$T_a$$ and can be explained by considering the variation of magnetic ordering. A close inspection into the temperature and composition dependence suggests a variation of magnetic phase transition temperature with composition and/or a possible correlation between the AHE and Fermi level position with respect to the Weyl points. Our comprehensive study would provide the basis for utilizing the unique functionalities of non-collinear antiferromagnetic materials.

論文

Intrinsic and extrinsic tunability of Rashba spin-orbit coupled emergent inductors

家田 淳一; 山根 結太*

Physical Review B, 103(10), p.L100402_1 - L100402_5, 2021/03

AA2020-0554.pdf:0.77MB

 被引用回数:13 パーセンタイル:80.58(Materials Science, Multidisciplinary)

The emergent induction of spiral magnets that was proposed [Nagaosa, Jpn. J. Appl. Phys. 58, 120909 (2019)] and recently demonstrated [Yokouchi et al., Nature 586, 232 (2020)] is shown to be further extended by a comprehensive treatment of the Rashba spin-orbit coupling and the electron spin relaxation that affect the underlying processes of spin-transfer torque and spinmotive force. Within adiabatic approximation, we show that the output voltages are widely altered intrinsically via the Rashba effect whereas extrinsically via the nonadiabatic correction due to the spin relaxation and sample disorder. The findings respectively clarify the origins for the amplitude modulation and sign change of the emergent inductance with tunability by electrical gating and careful sample preparation.

論文

Skyrmion-generated spinmotive forces in inversion broken ferromagnets

山根 結太*; 家田 淳一

Journal of Magnetism and Magnetic Materials, 491, p.165550_1 - 165550_5, 2019/12

AA2018-0522.pdf:0.4MB

 被引用回数:6 パーセンタイル:32.63(Materials Science, Multidisciplinary)

We present an analytical study on the spinmotive force (SMF) generated by translational motion of magnetic skyrmion. A SMF refers to an electrical voltage induced by dynamical magnetic textures, which reflects the spatiotemporal variation of the magnetization. The dynamics of a skyrmion thus can be detected by a SMF measurement, which may play an important role in future skyrmion-based technologies. We find the dependence of the SMF on skyrmion structure (e.g., skyrmion or anti-skyrmion, Neel or Bloch type, and the polarity of the skyrmion core) and Rashba and Dresselhaus spin-orbit couplings (SOCs). To this end, we derive explicit formulae for the spin-dependent electric fields originating from the two SOCs. Our findings offer a comprehensive understanding of the phenomenon and an estimation of the electrical voltage signal associated with a moving skyrmion for a given experiment.

論文

反強磁性ナノ構造におけるスピントルクと電圧生成

山根 結太*; 家田 淳一

まぐね, 13(5), p.235 - 241, 2018/10

AA2018-0148.pdf:0.6MB

We overview the recent theoretical development on spin-transfer torque in antiferromagnetic nanostructures and related subjects. As antiferromagnetic materials are generating more attention lately due to their potential to play pivotal roles in spintronics applications, demands are rising for reliable methods to control and detect antiferromagnetic textures and their dynamics. While antiferromagnets are largely insensitive to external magnetic fields in general, electrical means are proving to be capable of offering promising ways to access the antiferromagnetic dynamics. We discuss in this article the possibility of manipulation and observation of dynamical antiferromagnetic textures by electrical current and voltage.

論文

Spin-transfer torques in antiferromagnetic textures; Efficiency and quantification method

山根 結太*; 家田 淳一; Sinova, J.*

Physical Review B, 94(5), p.054409_1 - 054409_8, 2016/08

AA2016-0164.pdf:0.5MB

 被引用回数:25 パーセンタイル:74.97(Materials Science, Multidisciplinary)

反強磁性体におけるスピントランスファートルクの理論を定式化し、交換相互作用エネルギーが磁気副格子間の電子ダイナミクスの運動エネルギーに対して大きい場合と小さい場合の両者を取り扱う。本理論により、反強磁性体におけるスピントランスファートルクの効率が明確に定義された物質パラメータを用いて自然に導入される。この結果、電流は交換相互作用が相対的に大きな場合は反強磁性秩序関数と、逆に小さな場合は副格子傾斜磁化と、それぞれより強く結合することが判明した。またこの効果は、電流存在下での反強磁性スピン波分散関係の解析により定量化できる。特に、交換相互作用が相対的に大きな極限では、スピン波のドップラー効果が常に生じるのに対し、その逆の極限では副格子傾斜磁化が顕著となるようなモードにおいてのみ電流に対する応答が生じる。これらの知見は、入れ子構造や層状構造など様々な副格子構造をもつ反強磁性体におけるスピントランスファートルクの理解と設計に対する枠組みを与える。

論文

Electric voltage generation by antiferromagnetic dynamics

山根 結太*; 家田 淳一; Sinova, J.*

Physical Review B, 93(18), p.180408_1 - 180408_5, 2016/05

 被引用回数:16 パーセンタイル:61.47(Materials Science, Multidisciplinary)

We theoretically demonstrate dc and ac electric voltage generation due spinmotive forces originating from domain wall motion and magnetic resonance, respectively, in two-sublattice antiferromagnets. Our theory accounts for the canting between the sublattice magnetizations, the nonadiabatic electron spin dynamics, and the Rashba spin-orbit coupling. We predict that the spinmotive force can of the order of millivolt, several orders larger than their ferromagnetic counterparts. This work suggests a new way to observe and explore the dynamics of antiferromagnetic textures by electrical means.

論文

Spinmotive force due to motion of magnetic bubble arrays driven by magnetic field gradient

山根 結太*; Hemmatiyan, S.*; 家田 淳一; 前川 禎通; Sinova, J.*

Scientific Reports (Internet), 4, p.6901_1 - 6901_5, 2014/11

 被引用回数:14 パーセンタイル:52.39(Multidisciplinary Sciences)

局在磁化と電動電子の相互作用は、磁性材料における多彩な現象の源となっている。最近、磁化の時間的・空間的変化がスピン流とそれに伴う電圧を生成することが示された。この、スピン起電力と名付けられた効果は、次期構造の運動とその性質を探索する上で強力な方法であると同時に、起電力生成の新機構を与えるものである。本論文では、磁場勾配のもとにおかれた磁気バブル配列の系が電圧を生成することを理論的に明らかにする。発生する電圧の理論式を導出することで、電流駆動磁化ダイナミクスにおける非断熱性を記述する現象論的パラメータ$$beta$$の値を直接測定する手段を与える。このスピン起電力によって、磁場勾配を利用した新しいタイプのスピントロニクス素子開発への扉が開かれる。

論文

Spinmotive force with static and uniform magnetization induced by a time-varying electric field

山根 結太; 家田 淳一; 前川 禎通

Physical Review B, 88(1), p.014430_1 - 014430_4, 2013/07

 被引用回数:17 パーセンタイル:61.1(Materials Science, Multidisciplinary)

A new spinmotive force is predicted in ferromagnets with spin-orbit coupling. By extending the theory of spinmotive force, we show that a time-varying electric field can induce a spinmotive force with static and uniform magnetization. This spinmotive has two advantages; it can be detected free from the inductive voltage owing to the absence of dynamical magnetization, and it can be tuned by electric fields. To observe the effect, we propose two experimental setups: Electric voltage measurement in a single ferromagnet and spin injection from a ferromagnet into an attached nonmagnetic conductor.

論文

Real-time analysis of the spinmotive force due to domain wall motion

家田 淳一; 前川 禎通; 山根 結太

Journal of the Korean Physical Society, 62(12), p.1802 - 1806, 2013/06

 被引用回数:2 パーセンタイル:20.15(Physics, Multidisciplinary)

スピン起電力は、被一様磁化構造の実時間ダイナミクスを反映する。われわれは、数値シミュレーションを用いて磁壁移動に伴うスピン起電力の実時間解析を行い、磁壁運動の運動状態が非線形な場合においてもスピン起電力のDC成分は外部磁場に比例することを見いだした。外部磁場の強度を増やしていくと、出力起電力にスパイク状の信号が現れる。これは、磁壁内部にある磁気渦コアの生成・消滅現象に対応することを明らかにした。また、出力起電力と外部磁場の比例係数から、スピン分極率が求められる。この手法を用いることでさまざまな物質のスピン分極率を精確に決定することが可能である。

論文

Spinmotive force in magnetic nanostructures

家田 淳一; 山根 結太*; 前川 禎通

SPIN, 3(2), p.1330004_1 - 1330004_15, 2013/06

 被引用回数:5 パーセンタイル:15.32(Physics, Applied)

The mutual interaction between spin current and magnetization is a key phenomenon in spintronics. This interaction leads to a spinmotive force, a mechanism of energy-transfer from magnetization into conduction electrons. In this paper, the basic concepts and recent developments of the spinmotive force are introduced.

論文

Stability of spinmotive force in perpendicularly magnetized nanowires under high magnetic fields

山根 結太; 家田 淳一; 前川 禎通

Applied Physics Letters, 100(16), p.162401_1 - 162401_3, 2012/04

 被引用回数:7 パーセンタイル:30.56(Physics, Applied)

Spinmotive force induced by domain wall motion in perpendicularly magnetized nanowires is numerically demonstrated. We show that using nanowires with large magnetic anisotropy can lead to a high stability of spinmotive force under strong magnetic fields. We observe spinmotive force in the order of tens of $$mu$$V in a multilayered Co/Ni nanowire and several hundreds of $$mu$$V in a $$L$$1$$_{0}$$-ordered FePt nanowire; the latter is two orders of magnitude greater than that in permalloy nanowires reported previously. The narrow structure and low mobility of a domain wall under magnetic fields in perpendicularly magnetized nanowires permits downsizing of spinmotive force devices.

論文

Time-domain observation of the spinmotive force in permalloy nanowires

林 将光*; 家田 淳一; 山根 結太; 大江 純一郎*; 高橋 有紀子*; 三谷 誠司*; 前川 禎通

Physical Review Letters, 108(14), p.147202_1 - 147202_5, 2012/04

 被引用回数:37 パーセンタイル:82.27(Physics, Multidisciplinary)

磁壁移動に伴うスピン起電力を、パーマロイ細線における通常の誘導起電力を適切に差し引いた実時間電圧測定により直接検出する。磁壁の移動速度は印加磁場の大きさに対して非線形な振る舞いを示すが、出力電圧は磁場に対して線形となる。電圧信号の符号は、磁壁の運動方向に応じて反転することが示される。これらの振る舞いは、数値シミュレーションにより定量的に説明され、磁壁運動が周期的な磁化構造変化によって特徴付けられないような磁場領域にあったとしても、出力が外部磁場に対して線形に応答する様子が示される。

論文

Continuous generation of spinmotive force in a patterned ferromagnetic film

山根 結太; 捧 耕平*; 安 東秀*; 針井 一哉*; 大江 純一郎*; 家田 淳一; Barnes, S. E.*; 齊藤 英治; 前川 禎通

Physical Review Letters, 107(23), p.236602_1 - 236602_4, 2011/11

 被引用回数:45 パーセンタイル:85.72(Physics, Multidisciplinary)

We study, both experimentally and theoretically, the generation of a dc spinmotive force. By exciting a ferromagnetic resonance of a comb-shaped ferromagnetic thin film, a continuous spinmotive force is generated. Experimental results are well reproduced by theoretical calculations, offering a quantitative and microscopic understanding of this spinmotive force.

論文

Spinmotive force due to intrinsic energy of ferromagnetic nanowires

山根 結太; 家田 淳一; 大江 純一郎*; Barnes, S. E.*; 前川 禎通

Applied Physics Express, 4(9), p.093003_1 - 093003_3, 2011/09

 被引用回数:9 パーセンタイル:38.14(Physics, Applied)

We study, both analytically and numerically, a spinmotive force arising from inherent magnetic energy of a domain wall in a wedged ferromagnetic nanowire. In a spatially-nonuniform nanowire, domain walls are subjected to an effective magnetic field, resulting in spontaneous motion of the walls. The spinmotive force mechanism converts the ferromagnetic exchange and demagnetizing energy of the nanowire into the electrical energy of the conduction electrons through the domain wall motion. The calculations show that this spinmotive force can be several microvolts, which is easily detectable by experiments.

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