Phase transitions between helices, vortices, and hedgehogs driven by spatial anisotropy in chiral magnets
Phase transitions between helices, vortices, and hedgehogs driven by spatial anisotropy in chiral magnets
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DOI：
10.1103/physrevb.103.054427
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
K. Shimizu;S. Okumura;Y. Kato;Y. Motome
中科院分区：
文献类型：
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作者：
K. Shimizu;S. Okumura;Y. Kato;Y. Motome
自旋螺旋的叠加可以产生拓扑自旋纹理，如二维涡旋和skyrmions，以及三维刺猬。它们的拓扑性质和空间维度取决于组成螺旋的数量和相对方向。这允许通过控制空间各向异性在拓扑自旋纹理之间进行相互变换。本文从理论上研究了手征磁性金属有效自旋模型中磁相互作用的各向异性效应。通过对三重叠加和四重叠加两种情况的变分计算，我们发现各向同性情况下稳定的hedgehog晶格由于各向异性而发生形变，并最终转变为其他降维的自旋织构，如螺旋和涡旋。通过跟踪磁单极子和反单极子在实空间中的位置以及非共面自旋织构产生的磁场，我们也阐明了拓扑性质的变化。我们的研究结果表明可能的控制拓扑自旋纹理，例如，通过单轴压力和手性材料中的化学取代。
Superpositions of spin helices can yield topological spin textures, such as two-dimensional vortices and skyrmions, and three-dimensional hedgehogs. Their topological nature and spatial dimensionality depend on the number and relative directions of the constituent helices. This allows mutual transformation between the topological spin textures by controlling the spatial anisotropy. Here we theoretically study the effect of anisotropy in the magnetic interactions for an effective spin model for chiral magnetic metals. By variational calculations for both cases with triple and quadruple superpositions, we find that the hedgehog lattices, which are stable in the isotropic case, are deformed by the anisotropy, and eventually changed into other spin textures with reduced dimension, such as helices and vortices. We also clarify the changes of topological properties by tracing the real-space positions of magnetic monopoles and antimonopoles as well as the emergent magnetic field generated by the noncoplanar spin textures. Our results suggest possible control of the topological spin textures, e.g., by uniaxial pressure and chemical substitution in chiral materials.