Influence of heavy-metal capping layers on perpendicular magnetic anisotropy and spin-orbit torques of Pt/Co/HM stacks structures

Abstract

The influence of perpendicular magnetic anisotropy (PMA) and current-induced magnetization switching on different capping materials, especially heavy metal (HM) materials has been rarely studied. In this work, the dependence of HM capping layer on interfacial PMA and current-induced magnetization switching in Pt/Co/HM tri-layered structures were investigated, where HM is Ta, Pt and W. We found that the Co/HM interface play a significant role on the PMA. Especially, the structure with a Ta capping layer features the largest anisotropy energy density KU of 3.15 Merg/cm3 and the largest spin-orbit torques (SOT) switching efficiency ηSOT of 0.19, which can be attributed to the different spin-orbit coupling and interfacial hybridization between Co and HM layers. Furthermore, the Pt/Co/Ta structure has dissimilar metals (Pt and Ta) with opposite spin Hall angles on the opposite sides of the ferromagnetic Co. We also investigated the Co layer thickness tCo dependence of PMA and switching current density, indicating the lower switching field can reduce the switching current density in the PMA region.