Tunable spin–orbit torque efficiency in in-plane and perpendicular magnetized [Pt/Co]n multilayer

Abstract

Despite the great promise for very efficient and fast switching of magnetization in embedded memory and computing applications, the performance of spin–orbit torque (SOT) lags behind conventional technologies due to the low spin-Hall conductivity of the spin Hall materials. This work reports an advantageous spin Hall material, periodic [Pt/Co]n multilayer, which combines a low resistivity with a widely tunable spin Hall effect along with magnetization as evidenced with an in-plane CoFeB ferromagnetic detector. Three detection methods have been employed to illustrate the trends of magnetic orientation, interlayer exchange coupling, spin transport, and SOT efficiency as a function of Co thickness, which casts insight into the mechanisms of the SOTs in the [Pt/Co]n multilayer. With the varying Co thickness in the [Pt/Co]n multilayer, it is found that the damping-like torque efficiency is negative and the field-like torque efficiency is 8.2–31.5 times larger. The [Pt/Co]n multilayers have two spin reorientation transition states where the spin Hall angle θSH is maximized with a low resistivity of ∼ 40 μΩ cm, at tCo = 0.507 nm and 0.159 nm. We simulated the magnetization trajectories and time-domain responses of SOT switching with a current pulse and demonstrated a much faster switching in the spin reorientation transition states based on the coupled Landau–Lifshitz–Gilbert equation.