Enhancing Rashba Spin-Splitting Strength by Orbital Hybridization.

A Rashba spin-splitting state with spin-momentum locking enables the charge-spin interconversion known as the Rashba effect, induced by the interplay of inversion symmetry breaking (ISB) and spin-orbit coupling (SOC). Enhancing spin-splitting strength is promising to achieve high spin-orbit torque (SOT) efficiency for low-power-consumption spintronic devices. However, the energy scale of natural ISB at the interface is relatively small, leading to the weak Rashba effect. In this work, we report that orbital hybridization inducing additional asymmetry potential at the interface observably enhances spin-splitting strength, verified in the hexagonal boron nitride (h-BN)/CoPt heterostructures. First-principles calculations suggest the sizable Rashba spin-splitting derived from the out-of-plane - hybridization combined with SOC at the h-BN/CoPt interface. Then, the SOT efficiency is observably enhanced the Rashba effect at the h-BN/CoPt interface and exhibits unusual temperature dependence, in which the large-area h-BN is grown on the CoPt layer with perpendicular magnetic anisotropy by magnetron sputtering. Especially, the dominant damping-like torque is observed, resulting in the lower threshold switching current density and the enhanced switching ratio. Our results provide opportunities for interfacial control to enhance the Rashba effect and the SOT efficiency in heterostructures. It is expected to contribute to the design of energy-efficient spintronic devices.