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

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 theta (SH) is maximized with a low resistivity of similar to 40 mu Omega cm, at t(Co)=0.507nm and 0.159nm. 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.

Automated summary

This study reports a novel high-efficiency spin Hall material, achieved through the design of a multilayer structure that combines low resistivity and tunable spin Hall effect. Various detection methods were used to study the mechanism and efficiency of SOT in the [Pt/Co](n) multilayer, revealing important spin reorientation transition states.