Single-Layer Spin-Orbit-Torque Magnetization Switching Due to Spin Berry Curvature Generated by Minute Spontaneous Atomic Displacement in a Weyl Oxide

Abstract

Spin Berry curvature characterizes the band topology as the spin counterpart of Berry curvature and is crucial in generating novel spintronics functionalities. By breaking the crystalline inversion symmetry, the spin Berry curvature is expected to be significantly enhanced; this enhancement will increase the intrinsic spin Hall effect in ferromagnetic materials and, thus, the spin–orbit torques (SOTs). However, this intriguing approach is not applied to devices; generally, the spin Hall effect in ferromagnet/heavy-metal bilayer is used for SOT magnetization switching. Here, SOT-induced partial magnetization switching is demonstrated in a single layer of a single-crystalline Weyl oxide SrRuO₃ (SRO) with a small current density of ≈3.1 × 10⁶ A cm⁻². Detailed analysis of the crystal structure in the seemingly perfect periodic lattice of the SRO film reveals barely discernible oxygen octahedral rotations with angles of ≈5° near the interface with a substrate. Tight-binding calculations indicate that a large spin Hall conductivity is induced around small gaps generated at band crossings by the synergy of inherent spin‒orbit coupling and band inversion due to the rotations, causing magnetization reversal. The results indicate that a minute atomic displacement in single-crystal films can induce strong intrinsic SOTs that are useful for spin-orbitronics devices.