Temperature-dependent orbital torque in Ru/Co bilayers

Abstract

Efficient orbital transport in transition metals is central to the advancement of next-generation orbitronics. However, the fundamental scattering mechanisms governing orbital generation and relaxation remain elusive. Here, we report a comprehensive study of the temperature-dependent orbital torque in Ru/Co bilayer using spin–torque ferromagnetic resonance. We observe a pronounced enhancement in orbital torque efficiency upon cooling from 300 to 60 K, reaching an increase of approximately 55% in thick films. Thickness-dependent analysis reveals that this performance boost stems from a synergistic increase in both the effective orbital Hall conductivity and the orbital diffusion length. Scaling relations identify extrinsic skew scattering as the dominant generation mechanism and the Elliott–Yafet-like process as the primary relaxation pathway. These findings establish the fundamental scaling laws characterizing orbital transport in light metals, providing critical guidelines for designing thermally robust orbitronic applications.