Unconventional scaling of the orbital Hall effect

Orbital torque is a promising approach for electrically controlling magnetization in spintronic devices. However, unravelling the underlying mechanisms governing the orbital Hall effect (OHE), especially the role of extrinsic scattering and its scaling with conductivity (σ_xx), is crucial for realizing the full potential of orbital torque in energy-efficient spintronic devices. Here, using SrRuO₃ as a model system, we discover an unconventional scaling of orbital Hall conductivity ( ${\sigma }_{\mathrm{OH}}$ ) with tunable σ_xx. ${\sigma }_{\mathrm{OH}}$ remains constant at high σ_xx but exhibits a striking enhancement as σ_xx decreases, contrasting with spin Hall effect suppression at low σ_xx. This behaviour underscores the Dyakonov-Perel-like orbital relaxation mechanism as key to unconventional OHE. Leveraging this scaling, we achieve enhanced orbital torque via concurrent increases in orbital Hall conductivity and orbital Hall angle, demonstrating threefold power reduction in spin-orbit torque switching with moderate σ_xx reduction. Our work highlights the dominant role of extrinsic disorder scattering in unconventional OHE and establishes a transformative paradigm for energy-efficient spintronics.