Influence of MgO Sputtering Power and Post annealing on Strength and Angular Dependence of Spin-Orbit Torques in Pt/Co/MgO Trilayers

Abstract

The strength and angular dependence of the spin-orbit torques (SOTs) in Pt/Co/MgO trilayers are obtained by analyzing harmonic Hall voltage measurement results. The detailed analytical equations that consider both the isotropic and angle-dependent torques are derived and then used to characterize the angular dependence of the SOTs. The results show that both the dampinglike and fieldlike torques are strongly dependent on the polar angle of the magnetization and furthermore, the angle-dependent torques, combined with a strong contribution of the planar Hall effect, bring about the sign change of the out-of-phase Hall voltage signals. The SOT efficiencies are also investigated as a function of the MgO sputtering power density (P-MgO) and post annealing temperature in order to find the correlation between these parameters and the strength of the SOTs. A large change in SOT is observed depending on P-MgO and the field-like torque efficiency, for example, it is approximately 1.8 times higher at P-MgO = 4.39W/cm(2) than at P-MgO = 1.10W/cm(2) in the annealing temperature range of 250 degrees C - 350 degrees C.