Efficient charge to spin conversion in 5d transition metal oxide.*

With charge-based electronics reaching their limitations, more attention is being focused on developing systems utilizing spin currents. Recent focus has been on developing materials with a large spin Hall angle (SHA), the ratio of the charge to spin current density. Transition metal oxides such as iridium oxide IrO₂ are attractive candidates that have large conductivity and high spin-orbit coupling (SOC). IrO₂ possesses Dirac nodal lines in its band structure which is gapped by its strong SOC [1] which can generate large SHA. In this work, we have fabricated bilayers of IrO₂/Co₄₀Fe₄₀B₂₀­ samples to investigate the SHA in IrO₂ with different thicknesses and crystal structures. X-ray reflectivity, X-ray diffraction and atomic force microscopy have been used to verify the smoothness and crystallinity of IrO₂. We perform ST-FMR measurements on this system for different thicknesses of IrO₂ yielding SHA to be 40% in IrO₂ which is comparable to Pt. The resistivity of IrO₂ thin film is found to be 142 μΩ-cm, putting it in the metallic regime and close to that of CoFeB (120 μΩ-cm). Large SHA and high conductivity makes IrO₂ a robust candidate for further applications such as spin Hall nano-oscillators and magnetization switching.

[1] Sahoo et al. Adv. Quantum Technol. 4, 2000146 (2021)