Field-free spin–orbit torque driven multi-state reversal in wedged Ta/MgO/CoFeB/MgO heterostructures

• Published in: APL materials 2021-07, Vol.9 (7), p.071108-071108-5
• Main Authors: Li, Dong, Cui, Baoshan, Guo, Xiaobin, Xiao, Zhengyu, Zhang, Wei, Jia, Xiaoxiong, Duan, Jinyu, Liu, Xu, Chen, Jie, Quan, Zhiyong, Yu, Guoqiang, Xu, Xiaohong
• Format: Article
• Language: English
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/5.0053896

We report a current-induced four-state magnetization reversal under zero magnetic field in a wedged Ta/MgO/CoFeB/MgO heterostructure with a perpendicular magnetic anisotropy. Anomalous Hall effect and magneto-optical Kerr effect microscopy measurements were performed to demonstrate that the field-free multi-level reversal is jointly determined by the spin–orbit torque effective field that originates from the lack of the lateral inversion symmetry in the wedged stacking structure and the current-induced Oersted field. Moreover, the creation of robust intermediate Hall resistance states in the multi-state switching strongly depends on the current-induced Joule heating. Our results provide a route for the field-free multi-level state reversal, which is significant for fabricating the non-volatile and energy-efficient multi-level memories or artificial neuron devices.