Enhancing Rashba\nSpin-Splitting Strength by Orbital\nHybridization

A Rashba spin-splitting state with spin-momentum locking\nenables\nthe charge–spin interconversion known as the Rashba effect,\ninduced by the interplay of inversion symmetry breaking (ISB) and\nspin–orbit coupling (SOC). Enhancing spin-splitting strength\nis promising to achieve high spin–orbit torque (SOT) efficiency\nfor low-power-consumption spintronic devices. However, the energy\nscale of natural ISB at the interface is relatively small, leading\nto the weak Rashba effect. In this work, we report that orbital hybridization\ninducing additional asymmetry potential at the interface observably\nenhances spin-splitting strength, verified in the hexagonal boron\nnitride (h-BN)/Co<sub>3</sub>Pt heterostructures. First-principles\ncalculations suggest the sizable Rashba spin-splitting derived from\nthe out-of-plane <i>p</i>–<i>d</i> hybridization\ncombined with SOC at the h-BN/Co<sub>3</sub>Pt interface. Then, the\nSOT efficiency is observably enhanced <i>via</i> the Rashba\neffect at the h-BN/Co<sub>3</sub>Pt interface and exhibits unusual\ntemperature dependence, in which the large-area h-BN is <i>in\nsitu</i> grown on the Co<sub>3</sub>Pt layer with perpendicular\nmagnetic anisotropy by magnetron sputtering. Especially, the dominant\ndamping-like torque is observed, resulting in the lower threshold\nswitching current density and the enhanced switching ratio. Our results\nprovide opportunities for interfacial control to enhance the Rashba\neffect and the SOT efficiency in heterostructures. It is expected\nto contribute to the design of energy-efficient spintronic devices.