Resting on multi-scale modelling simulations, we explore dynamical aspects characterizing magnetic skyrmions driven by spin-transfer-torque towards repulsive and pinning 3d and 4d single atomic defects embedded in a Pd layer deposited on the Fe/Ir(111) surface. The latter is known to host sub-10 nm skyrmions which are of great interest in information technology. The Landau-Lifshitz-Gilbert equation is parametrized with magnetic exchange interactions extracted from the ab-initio all-electron full potential Korringa-Kohn-Rostoker Green function method, where spin-orbit coupling is added self-consistently. Depending on the nature of the defect and the magnitude of the applied magnetic field, the skyrmion deforms by either shrinking or increasing in size, experiencing thereby elliptical distortions. After applying a magnetic field of 10 Tesla, ultrasmall skyrmions are driven along a straight line towards the various defects which permits a simple analysis of the impact of the impurities. Independently from the nature of the skyrmion-defect complex interaction, being repulsive or pinning, a gyrotropic motion is observed. A repulsive force leads to a skyrmion trajectory similar to the one induced by an attractive one. We unveil that the circular motion is clockwise around pinning impurities but counter clockwise around the repulsive ones, which can be used to identify the interaction nature of the defects by observing the skyrmions trajectories. Moreover, and as expected, the skyrmion always escapes the repulsive defects in contrast to the pinning defects, which require a minimal depinning current to observe impurity avoidance. This unveils the richness of the motion regimes of skyrmions. We discuss the results of the simulations in terms of the Thiele equation, which provides a reasonable qualitative description of the observed phenomena. Finally, we show an example of a double track made of pinning impurities, where the engineering of their mutual distance allows to control the skyrmion motion with enhanced velocity.

中文翻译：

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PdFe/Ir(111) 表面电流驱动超小斯格明子的杂质相关回旋运动、偏转和钉扎

在多尺度建模模拟的基础上，我们探索了表征由自旋转移扭矩驱动的磁性斯格明子的动力学方面，以排斥和钉扎嵌入在 Fe/Ir(111) 表面上沉积的 Pd 层中的 3d 和 4d 单原子缺陷。众所周知，后者拥有亚 10 纳米的斯格明子，这在信息技术中引起了极大的兴趣。Landau-Lifshitz-Gilbert 方程使用从 ab-initio 全电子全势 Korringa-Kohn-Rostoker 格林函数方法中提取的磁交换相互作用进行参数化，其中自洽地添加自旋轨道耦合。根据缺陷的性质和外加磁场的大小，斯格明子通过缩小或增加尺寸而变形，从而经历椭圆形畸变。施加 10 特斯拉的磁场后，超小斯格明子沿着直线被驱动到各种缺陷，这允许对杂质的影响进行简单的分析。独立于skyrmion-缺陷复杂相互作用的性质，排斥或钉扎，观察到回旋运动。排斥力导致斯格明子轨迹类似于由吸引力引起的轨迹。我们揭示了圆周运动围绕钉扎杂质顺时针旋转，而围绕排斥杂质逆时针旋转，这可用于通过观察斯格明子轨迹来识别缺陷的相互作用性质。此外，正如预期的那样，与钉扎缺陷相比，斯格明子总是逃避排斥缺陷，钉扎缺陷需要最小的脱钉电流来观察杂质避免。这揭示了斯格明子运动机制的丰富性。我们根据 Thiele 方程讨论模拟结果，该方程为观察到的现象提供了合理的定性描述。最后，我们展示了一个由钉扎杂质制成的双轨道的例子，其中它们相互距离的工程允许以更高的速度控制斯格明子运动。