Giant Enhancement of Perpendicular Magnetic Anisotropy and Field-Free Switching Through Interfacial Engineering in Pt/Co/Pt Heterostructures

The enhancement of perpendicular magnetic anisotropy (PMA) is critical for the continuous growth of magnetic memory density. Material systems that possess 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 the interfacial PMA has been less investigated. This study demonstrated that 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 enhanced the effective PMA energy (K_\rm eff) by a factor of 4. First-principles calculations revealed that the underlying mechanism originated from Cr-Pt d-orbital hybridization, leading to a corresponding orbital redistribution and significantly increasing the magnetic anisotropy energy. The progressive reduction in the spin-orbit torque (SOT) efficiency with increasing Cr thickness might stem from the enhanced orbital Rashba-Edelstein effect at the Pt/Cr interface. Furthermore, the wedging of a few atomic Cr layers caused the robust field-free SOT switching of perpendicular magnetization, which was due to the lateral PMA gradients enabled by the strong dependence of the PMA on the Cr thickness. The results provide a method for interfacial PMA enhancement by d-orbital hybridization of 3d-5d electrons and an alternative to field-free SOT switching towards low-power and high-density memory applications.