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論文

Room-temperature flexible manipulation of the quantum-metric structure in a topological chiral antiferromagnet

Han, J.*; 内村 友宏*; 荒木 康史; Yoon, J.-Y.*; 竹内 祐太郎*; 山根 結太*; 金井 駿*; 家田 淳一; 大野 英男*; 深見 俊輔*

Nature Physics, 21 Pages, 2024/04

https://doi.org/10.1038/s41567-024-02476-2
 被引用回数：0 パーセンタイル：0.01

量子状態の幾何学的構造を特徴づける基礎的な量として、「量子計量」と「ベリー曲率」が存在する。ベリー曲率は、凝縮系において多種の重要な現象に寄与することが知られている。一方、量子計量も新たなトポロジカル物理現象の起源となることが予想されているが、特に常温常圧下においては、その効果はほとんど探索されていない。本研究では、トポロジカルカイラル反強磁性体Mn$$_{3}$$Snと白金の接合系を用い、界面でのナノスピン構造を介して、電子系の量子計量構造の制御に成功した。ベリー曲率ではなく量子計量特有の効果として、時間反転反対称でかつ電子散乱に対して頑強な、二次非線形ホール効果を測定した。更に、界面スピン構造は弱磁場及び界面スピン軌道相互作用によって急峻に変調されるため、量子計量構造も鋭敏に制御可能であることを示した。本研究成果により、量子状態に内在する量子計量構造を活用したトポロジカル物理現象が室温環境下でも可能になり、且つ応用面においても非線形素子を構築する助けとなることが期待される。

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

https://doi.org/10.1063/5.0135709
 被引用回数：2 パーセンタイル：66.71(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

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

https://doi.org/10.1063/5.0089355
 被引用回数：11 パーセンタイル：85.25(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

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

https://doi.org/10.1038/s41563-021-01005-3
 被引用回数：84 パーセンタイル：98.69(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

https://doi.org/10.1063/5.0043192
 被引用回数：14 パーセンタイル：77.78(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.

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