Giant enhancement of perpendicular magnetic anisotropy and field-free switching through interfacial engineering in Pt/Co/Pt heterostructures

Enhancement of perpendicular magnetic anisotropy (PMA) is critical for the continuous growth of magnetic memory density. The reported material systems possessing high interfacial PMA typically involve strong spin-orbit coupling (SOC) or transition metal/oxide interfaces. In contrast, the role of 3d light metals in enhancing interfacial PMA is less investigated. In this work, it is demonstrated the insertion of a few atomic Cr layers into Pt/Co/Pt/Ta heterostructures with Cr between the 1 atomic Pt layer and the 3 nm Ta overlayer is able to enhance the effective PMA energy (K_eff) by a factor of 4. First-principles calculations reveal that the underlying mechanism originates from Cr-Pt d-orbital hybridization, leading to a corresponding orbital redistribution and a significant rise in magnetic anisotropy energy. The progressive reduction in SOT efficiency with increasing Cr thickness might stems from the enhanced orbital Rashba-Edelstein effect at the Pt/Cr interface. Furthermore, through the wedging of a few atomic Cr layers a robust field-free spin-orbit torque switching of perpendicular magnetization is observed, which is due to the lateral PMA gradients enabled by the strong dependence of PMA on the Cr thickness. The presented resultsprovide a way for interfacial PMA enhancement by d-orbital hybridization of 3d-5d electrons, and offer an alternative for field-free SOT switching towards low power and high density memory applications.