Shigenaga Takayuki, Leonov Andrey O
International Institute for Sustainability with Knotted Chiral Meta Matter, Kagamiyama, Higashihiroshima 739-8511, Hiroshima, Japan.
Department of Chemistry, Faculty of Science, Hiroshima University Kagamiyama, Higashihiroshima 739-8526, Hiroshima, Japan.
Nanomaterials (Basel). 2023 Jul 14;13(14):2073. doi: 10.3390/nano13142073.
The skyrmion Hall effect, which is regarded as a significant hurdle for skyrmion implementation in thin-film racetrack devices, is theoretically shown to be suppressed in wedge-shaped nanostructures of cubic helimagnets. Under an applied electric current, ordinary isolated skyrmions with the topological charge 1 were found to move along the straight trajectories parallel to the wedge boundaries. Depending on the current density, such skyrmion tracks are located at different thicknesses uphill along the wedge. Numerical simulations show that such an equilibrium is achieved due to the balance between the Magnus force, which instigates skyrmion shift towards the wedge elevation, and the force, which restores the skyrmion position near the sharp wedge boundary due to the minimum of the edge-skyrmion interaction potential. Current-driven dynamics is found to be highly non-linear and to rest on the internal properties of isolated skyrmions in wedge geometries; both the skyrmion size and the helicity are modified in a non-trivial way with an increasing sample thickness. In addition, we supplement the well-known theoretical phase diagram of states in thin layers of chiral magnets with new characteristic lines; in particular, we demonstrate the second-order phase transition between the helical and conical phases with mutually perpendicular wave vectors. Our results are useful from both the fundamental point of view, since they systematize the internal properties of isolated skyrmions, and from the point of view of applications, since they point to the parameter region, where the skyrmion dynamics could be utilized.
斯格明子霍尔效应在立方手性磁体的楔形纳米结构中从理论上被证明是可以被抑制的，而该效应被认为是斯格明子在薄膜赛道器件中应用的一个重大障碍。在施加电流的情况下，发现具有拓扑电荷1的普通孤立斯格明子会沿着平行于楔形边界的直线轨迹移动。根据电流密度的不同，这种斯格明子轨迹位于楔形上坡的不同厚度处。数值模拟表明，这种平衡是由于马格努斯力（促使斯格明子向楔形高处移动）与因边缘斯格明子相互作用势最小而使斯格明子恢复到尖锐楔形边界附近位置的力之间的平衡而实现的。发现电流驱动的动力学是高度非线性的，并且取决于楔形几何结构中孤立斯格明子的内部特性；随着样品厚度的增加，斯格明子尺寸和螺旋度都会以一种非平凡的方式发生改变。此外，我们用新的特征线补充了手性磁体薄层中著名的状态理论相图；特别是，我们展示了具有相互垂直波矢的螺旋相和锥相之间的二级相变。我们的结果从基础角度来看是有用的，因为它们系统化了孤立斯格明子的内部特性，从应用角度来看也是有用的，因为它们指出了可以利用斯格明子动力学的参数区域。
