An emergent topological particle in magnets, skyrmion, has several unique features distinct from the other magnetic textures such as domain wall, helical structure, and vortex. It is characterized by a topological integer called skyrmion number N _sk , which counts how many times the directions of the magnetic moments wrap the unit sphere. This N _sk gives the chiral nature of the skyrmion dynamics, and leads to the extremely small critical current density j _c for the current-driven motion in terms of spin transfer torque effect. The finite j _c indicates the pinning effect due to the disorder such as impurities and defects, and the behaviors of skyrmions under disorder have not been explored well theoretically although it is always relevant in real systems. Here we reveal by a numerical simulation of Landau-Lifshitz-Gilbert equation that there are four different skyrmion phases with the strong disorder, i.e., (A) pinned state, (B) depinned state, (C) skyrmion multiplication/annihilation, and (D) segregation of skyrmions, as the current density increases, while only two phases (A) and (B) appear in the weak disorder case. The microscopic mechanisms of the new phases (C) and (D) are analyzed theoretically. These results offer a coherent understanding of the skyrmion dynamics under current with disorder.

中文翻译：

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无序磁体中电流驱动的天空离子理论。

磁体中出现的拓扑粒子skyrmion具有一些不同于其他磁性纹理的独特特征，例如畴壁，螺旋结构和涡旋。它的特征是称为skyrmion数N _sk的拓扑整数，该整数计算磁矩的方向包裹单位球体的次数。该N _sk给出了天窗离子动力学的手性，并且就自旋传递转矩效应而言，导致电流驱动运动的临界电流密度j _c非常小。有限j _c表示由于诸如杂质和缺陷之类的无序现象引起的钉扎效应，尽管在实际系统中它始终是相关的，但在理论上尚未很好地研究无序状态下的天蝎子的行为。在这里，我们通过Landau-Lifshitz-Gilbert方程的数值模拟揭示出，有四个具有强无序性的Skyrmion相，即（A）固定状态，（B）固定状态，（C）Skyrmion倍增/ an灭和（ D）随着电流密度的增加，分离Skyrmion，而在弱无序情况下只有两个阶段（A）和（B）出现。从理论上分析了新相（C）和（D）的微观机理。这些结果对当前有序的天体离子动力学有一个连贯的理解。