Narrow magnetic vortex dynamics in easy-plane anisotropy films induced by spin-transfer torque and spin-orbit torque

Abstract

Magnetic vortex is characterized by a magnetization curling in-plane around a vortex core which points out of the plane.[1] Recently another topologic defect, skyrmion having nanometer scale size, attracted great interest since it can be moved by low current density and thus opening new routes for massive information storage devices.[2] However, skyrmions exist only within a relatively narrow range of magnetic fields and temperatures and thus are difficult to stabilize and manipulate at RT. Therefore, one purpose of our study is to focus on ultra-small vortices in a ferromagnetic system with strong easy-plane magnetic anisotropy (so-called XY model[3,4]). Depending on the easy-plane anisotropy, the size of the vortex core can be less than 10nm while typically in soft ferromagnetic material such as NiFe, it is more than 20nm. On the other hand, current induced magnetic vortex dynamics has been studied both from theoretical and experimental points of view,[5,6] especially taking into account the spin-transfer torque (STT) generated by a spin polarized current. However, effects of another novel phenomenal, i.e., current induced spin-orbit torque (SOT) by spin Hall effect (SHE) on magnetic vortices starts to be of great interest. A comparison between the dynamics under STT and SOT was carried out in this study.