Topological magnetic domains exhibit many fascinating features and great potential in information storage and spintronics owing to their unique spin textures. In order to investigate the topological properties of the domain structures, the spontaneous evolutions of magnetic moments are evaluated by using Landau–Lifshitz–Gilbert equation. The equilibrium phase diagrams of the system with randomly, radial and axial distributed initial magnetic moments have been studied in detail. Simulation results show that the changes of quality factor (Q) and aspect ratio (T/D) lead to great differences in magnetization process under different initial magnetization states. Vortex, biskyrmion, skyrmion and bubble are formed as the value of Q gradually increases from 0 to 1. The system with Q < 0.5 is easy to stabilize into a vortex state, while the magnetic moments of the system with Q > 1.0 are arranged along the easy axis. When Q and T/D are in the range of 0.6 ~ 0.8 and 0.10 ~ 0.16, respectively, it is conducive to the formation of nontrivial topological domain. Biskyrmion is spontaneously formed in the system of Q = 0.6 and T/D = 0.12, proving that skyrmion-like domain can be generated in the absence of Dzyaloshinskii–Moriya interaction or external field.

中文翻译：

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磁性纳米盘平衡状态下非平凡拓扑域结构的探索

由于其独特的自旋纹理，拓扑磁畴在信息存储和自旋电子学中表现出许多迷人的特征和巨大的潜力。为了研究畴结构的拓扑特性，使用Landau-Lifshitz-Gilbert方程评估磁矩的自发演化。详细研究了具有随机、径向和轴向分布的初始磁矩系统的平衡相图。仿真结果表明，品质因数（Q）和纵横比（T/D）的变化导致不同初始磁化状态下的磁化过程存在较大差异。随着 Q 值从 0 逐渐增加到 1，形成 Vortex、biskyrmion、skyrmion 和气泡。 Q < 0.5 的系统容易稳定到涡流状态，而 Q > 1.0 的系统的磁矩沿易轴排列。当Q和T/D分别在0.6～0.8和0.10～0.16范围内时，有利于非平凡拓扑域的形成。Biskyrmion 在 Q = 0.6 和 T/D = 0.12 的系统中自发形成，证明在没有 Dzyaloshinskii-Moriya 相互作用或外部场的情况下可以产生类 Skyrmion 域。