Experimental observation and micromagnetic understanding of the current-induced magnetization reversal process in Ta/Pt/[Co/Ni] n Co/Ta multilayers

We investigated current-induced magnetization reversal process mediated by spin-orbit torque (SOT) in Ta/Pt/(Co/Ni)nCo/Ta multilayers experimentally and by micromagnetic simulation. The experiment results show that the current-induced magnetization reversal in these samples is completed by nucleation and subsequent domain wall (DW) propagation. For the samples with small number (n) of Co/Ni bi-layers, which show strong Dzyaloshinskii-Moriya interaction (DMI), when the in-plane magnetic field (Hx) is weaker than a critical value, the tilted DWs form in the final stabilized state, corresponding to a partial magnetization reversal. As Hx is close to the DMI effective field, the domains expand to semicircular areas asymmetrically, resulting in complete magnetization reversal finally. For the sample with large n and weak DMI, the reversed domains grow obliquely along a special orientation, which varies with the magnitude of Hx. These experimental phenomena were well reproduced by micromagnetic simulation after taking account of SOT effect and the DMI-modulated magnetic moment distribution in the DW. The agreement between the experimental observation and micromagnetic simulation suggest that the current-induced magnetization reversal process in Ta/Pt/[Co/Ni]nCo/Ta system can be well understood in the frame of SOT and DMI scenario.