单轴手性磁体中的螺旋性

中文摘要 AI 辅助

被非磁性介质（如空气或真空）包围的单轴手性磁体的平衡态是螺旋织构，其特征为单一且明确的波矢，这类系统中从未观测到亚稳态。然而，近期研究表明，当手性磁体与两个单轴铁磁体紧密接触时，除平衡态外还会出现大量亚稳态螺旋态[Phys. Rev. B 109, 214424]，这些螺旋态通过其波数（螺旋性）区分。本研究阐明了这些态稳定化的拓扑起源——一种我们称之为动力学拓扑保护的机制，并探究了其静态与动态性质。我们发现，受该动力学拓扑保护的影响，在施加足够弱的磁场和极化电流时，螺旋态的卷绕数保持恒定。此外，当向亚稳态螺旋态施加极化电流时，会达到一种静态构型，该构型保留原始卷绕数，但其卷绕数密度呈非均匀分布，集中在与其中一个铁磁体的界面附近。对足够大的磁场和电流的动态响应提供了在不同螺旋态之间切换的机制。由于磁性质依赖于螺旋性，这些亚稳态螺旋态在自旋电子学和磁子学领域具有极高的应用潜力。

英文摘要

The equilibrium state of a monoaxial chiral magnet surrounded by a non-magnetic medium (such as air or vacuum) is a helical texture characterized by a single, well-defined wave vector. No metastable states have ever been observed in such systems. Recently, however, it was demonstrated that when a chiral magnet is in close contact with two uniaxial ferromagnets, a large number of metastable helical states emerge in addition to the equilibrium state [Phys. Rev. B 109, 214424]. These helical states are distinguished by their wave number (helicity). In the present work, we elucidate the topological origin of the stabilization of these states --a mechanism we term dynamical topological protection-- and investigate their static and dynamic properties. We find that, as a consequence of this dynamical topological protection, the winding number of the helical states remains constant under the application of sufficiently weak magnetic fields and polarized electric currents. Furthermore, when a polarized current is applied to a metastable helical state, a static configuration is reached. This state retains the original winding number, but its winding number density becomes non-homogeneously distributed, concentrating near the interface with one of the ferromagnets. The dynamic response to sufficiently large magnetic fields and currents provides mechanisms to switch between different helical states. Since the magnetic properties depend on helicity, these metastable helical states are highly promising for applications in spintronics and magnonics.

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14 pages