Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113 8656, Japan.
Nat Commun. 2013;4:1463. doi: 10.1038/ncomms2442.
Current-driven motion of the magnetic domain wall in ferromagnets is attracting intense attention because of potential applications such as racetrack memory. There, the critical current density to drive the motion is ~10(9)-10(12) A m(-2). The skyrmions recently discovered in chiral magnets have much smaller critical current density of ~10(5)-10(6) A m(-2), but the microscopic mechanism is not yet explored. Here we present a numerical simulation of Landau-Lifshitz-Gilbert equation, which reveals a remarkably robust and universal current-velocity relation of the skyrmion motion driven by the spin-transfer-torque unaffected by either impurities or nonadiabatic effect in sharp contrast to the case of domain wall or spin helix. Simulation results are analysed using a theory based on Thiele's equation, and it is concluded that this behaviour is due to the Magnus force and flexible shape-deformation of individual skyrmions and skyrmion crystal, which enable them to avoid pinning centres.
由于在诸如赛道式存储器等方面的潜在应用，当前铁磁体中磁畴壁的电流驱动运动引起了人们的强烈关注。在这些应用中，驱动运动的临界电流密度约为 10(9)-10(12)A/m(2)。最近在手性磁体中发现的螺旋磁子具有小得多的临界电流密度，约为 10(5)-10(6)A/m(2)，但其微观机制尚未得到探索。在这里，我们提出了 Landau-Lifshitz-Gilbert 方程的数值模拟，该模拟揭示了由自旋转移扭矩驱动的螺旋磁子运动的一种非常稳健且普遍的电流-速度关系，与畴壁或螺旋磁子的情况形成鲜明对比，后两者不受杂质或非绝热效应的影响。使用基于 Thiele 方程的理论对模拟结果进行了分析，得出的结论是，这种行为归因于单个螺旋磁子和螺旋磁子晶体的马格努斯力和灵活的形状变形，这使它们能够避免钉扎中心。
