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

• Main Authors: Dong Li, Baoshan Cui, Xiaobin Guo, Zhengyu Xiao, Wei Zhang, Xiaoxiong Jia, Jinyu Duan, Xu Liu, Jie Chen, Zhiyong Quan, Guoqiang Yu, Xiaohong Xu
• Format: Article
• Language: English
• Published: AIP Publishing LLC 2021-07-01
• Series: APL Materials
• Online Access: http://dx.doi.org/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.