School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, PR China.
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, 21218, USA.
Sci Rep. 2017 May 17;7(1):2047. doi: 10.1038/s41598-017-02208-y.
In materials with the gradient of magnetic anisotropy, spin-orbit-torque-induced magnetization behaviour has attracted attention because of its intriguing scientific principle and potential application. Most of the magnetization behaviours microscopically originate from magnetic domain wall motion, which can be precisely depicted using the standard cooperative coordinate method (CCM). However, the domain wall motion in materials with the gradient of magnetic anisotropy using the CCM remains lack of investigation. In this paper, by adopting CCM, we established a set of equations to quantitatively depict the spin-orbit-torque-induced motion of domain walls in a Ta/CoFe nanotrack with weak Dzyaloshinskii-Moriya interaction and magnetic anisotropy gradient. The equations were solved numerically, and the solutions are similar to those of a micromagnetic simulation. The results indicate that the enhanced anisotropy along the track acts as a barrier to inhibit the motion of the domain wall. In contrast, the domain wall can be pushed to move in a direction with reduced anisotropy, with the velocity being accelerated by more than twice compared with that for the constant anisotropy case. This substantial velocity manipulation by anisotropy engineering is important in designing novel magnetic information devices with high reading speeds.
在具有磁各向异性梯度的材料中，自旋轨道转矩诱导的磁化行为因其有趣的科学原理和潜在的应用而引起了关注。大多数微观磁化行为源自磁畴壁运动，可以使用标准的协同坐标方法（CCM）精确地描述。然而，对于具有磁各向异性梯度的材料中的畴壁运动，CCM 的应用仍然缺乏研究。在本文中，我们采用 CCM 建立了一组方程，以定量描述具有弱 Dzyaloshinskii-Moriya 相互作用和磁各向异性梯度的 Ta/CoFe 纳米线中的自旋轨道转矩诱导畴壁运动。通过数值求解方程，得到的解与微磁模拟的解相似。结果表明，沿轨道增强的各向异性起到了阻碍畴壁运动的作用。相反，畴壁可以被推向各向异性降低的方向移动，其速度比各向异性常数情况下的速度快两倍以上。这种通过各向异性工程实现的显著速度控制对于设计具有高速读取速度的新型磁信息器件非常重要。
