The modulation of perpendicular magnetic anisotropy and spin-orbit toque in Pt/Co/Pt multilayers with interfacial decoration by insertion of Bi layer

Abstract Bismuth is a well-known semimetal material with strong spin-orbit coupling (SOC) and has been confirmed to exhibit a larger spin Hall angle (SHA) in CuBi and PtBi alloys with low Bi doping concentration. In this study, we investigated perpendicular magnetic anisotropy (PMA) and spin–orbit torques (SOTs) in Pt/Co/Pt multilayers by inserting a Bi layer with a thickness of 2 nm. Two types of PMA multilayers, Pt(3 nm)/Co(1 nm)/Pt(5 nm) and Pt(3 nm)/Co(1 nm)/Pt(1 nm), with different spin accumulations, were designed and prepared by varying the top Pt thickness. A significant enhancement of PMA and SOT efficiency is observed in the multilayer with a thick top Pt thickness after inserting a Bi layer at the Co/Pt interface. However, for Pt/Co/Pt multilayers with a thin top Pt thickness, both PMA and SOT efficiency decrease with the insertion of a Bi layer at the Co/Pt interface. Meanwhile, the sign of SOTs changes in the two types of Pt/Co/Pt multilayers when introducing a Bi layer. This completely opposite behavior illustrates that the Bi/Pt interface plays an important role in modulating the PMA and SOT efficiency of Pt/Co/Bi/Pt multilayers. Minimizing the intermixing of Bi/Pt proves to be an effective approach to increase the PMA and SOT efficiency of Pt/Co/Bi/Pt multilayers.