Asymmetric magnetic domain wall motion under lateral and normal space inversion asymmetry with interfacial Dzyaloshinskii–Moriya interaction

The magnetic anisotropy of a typical magnetic sample with an easy axis perpendicular to the surface has many advantages over an in-plane easy axis due to advantages like better thermal stability, higher data storage density, lower energy consumption, etc. The perpendicular magnetic anisotropy arises due to the spatial inversion asymmetry (SIA) at the interfaces between a ferromagnet (FM) and a heavy metal (HM). In such systems, one can achieve a current-induced magnetization reversal (CIMR) via spin–orbit torque with the assistance of an in-plane (IP) magnetic field. This IP field requirement for the CIMR process is an obstacle for the practical application. Recent studies on CIMR at magnetic fields free condition are achieved by breaking the lateral structural symmetry by achieving thickness-gradient in a particular layer. In previous reports, the SIA normal to the surface in a heterostructure leads to an asymmetric contribution as chiral damping. In this work, a system Ta/Pt/CoFeB/Pt with normal and lateral SIA has been prepared by introducing a thickness-gradient in the FM CoFeB layer, which leads to create a tilted perpendicular magnetic anisotropy. The presence of the lateral SIA gives rise to another asymmetric component besides the chiral damping component. In this study, the total asymmetric component of the Ta/Pt/CoFeB/Pt heterostructure has been calculated into two contributions H t and H c h , to extract the distinct information of the tilt asymmetry due to the lateral SIA and the chiral damping due to the normal SIA, respectively. In this study, by varying the bottom Pt thickness of the Ta/Pt/CoFeB/Pt heterostructures we have observed that the two asymmetry contributions H t and H c h both decreased with increasing bottom Pt thickness.