直流与交流压缩过程中的自发斯格明子共形晶格及横向运动
Spontaneous Skyrmion Conformal Lattice and Transverse Motion During dc and ac Compression
AI总结：
本文用原子尺度模拟揭示直流和交流压缩下铁磁斯格明子形成尺寸—密度梯度共形晶格，并由 Magnus 力诱发横向运动、棘轮泵及剪切带。
摘要：
我们采用基于原子尺度的模拟，研究铁磁斯格明子在直流和交流驱动下被持续压向刚性壁时的行为。被压缩的斯格明子可能在壁附近湮灭，并形成同时具有尺寸梯度和密度梯度的共形晶体，这使其不同于此前在超导涡旋和胶体颗粒中观察到的共形晶体。对于直流和交流驱动，斯格明子都能因密度梯度与尺寸梯度的共同作用而沿垂直于压缩方向运动。压缩方向上的力通过 Magnus 力转化为横向运动。在交流驱动下，斯格明子的湮灭数量减少，并且我们发现了斯格明子 Magnus 棘轮泵效应。我们还观察到剪切带现象，其中靠近壁的斯格明子运动速度最高可达远离壁的斯格明子的两倍。当改变所施加驱动的大小时，我们发现存在一个临界电流，超过该电流后，斯格明子会在一个取决于驱动大小的时间尺度内完全湮灭。通过改变磁性参数，我们发现横向运动强烈依赖于斯格明子尺寸。较小的斯格明子更具刚性，这会干扰尺寸梯度并破坏横向运动。我们还通过将原子尺度模拟与基于粒子的模型进行比较，证实了尺寸梯度的作用；在该模型中，我们发现横向运动只是瞬态的。我们的结果与斯格明子遇到排斥性磁壁、畴壁或界面的应用相关。
英文摘要：
We use atomistic-based simulations to investigate the behavior of ferromagnetic skyrmions being continuously compressed against a rigid wall under dc and ac drives. The compressed skyrmions can be annihilated close to the wall and form a conformal crystal with both a size and a density gradient, making it distinct from conformal crystals observed previously for superconducting vortices and colloidal particles. For both dc and ac driving, the skyrmions can move transverse to the compression direction due to a combination of density and size gradients. Forces in the compression direction are converted by the Magnus force into transverse motion. Under ac driving, the amount of skyrmion annihilation is reduced and we find a skyrmion Magnus ratchet pump. We also observe shear banding in which skyrmions near the wall move up to twice as fast as skyrmions further from the wall. When we vary the magnitude of the applied drive, we find a critical current above which the skyrmions are completely annihilated during a time scale that depends on the magnitude of the drive. By varying the magnetic parameters, we find that the transverse motion is strongly dependent on the skyrmion size. Smaller skyrmions are more rigid, which interferes with the size gradient and destroys the transverse motion. We also confirm the role of the size gradient by comparing our atomistic simulations with a particle-based model, where we find that the transverse motion is only transient. Our results are relevant for applications where skyrmions encounter repulsive magnetic walls, domain walls, or interfaces.
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