Magneto-Optic Measurement of Surface Spin Accumulation in RuO2 Resulting from Spin-Split Band Structure

Spin transport in topological insulators and antiferromagnets have been extensively studied for spintronic applications due to their potential of providing larger spin Hall angle than conventional spin Hall metals, such as Pt or W. The two collinear spin sublattices in the rutile crystal structure of the metal antiferromagnet RuO2 are related by time reversal and a 90-degree lattice rotation with respect to the c-axis [1]. Such crystallographic and magnetic structure give rise to a spin-split band structure and results in the generation of a spin current in the presence of a charge current with spin polarization parallel to the Néel vector. Spin Hall angle in RuO2 is theoretically [2] shown to be larger than Pt and W. Suitable canting of the Néel vector can result in a surface spin accumulation with a strong out-of-plane spin component which allows optical detection of the spins via the magneto-optic Kerr effect (MOKE). In this work, we use MOKE with a high sensitivity of 28 nrad/√Hz to experimentally study the spin Hall effect in RuO2. Our results show that RuO2 exhibits Kerr signals as large as 100 nrad in the presence of a charge current. Results from different crystal orientations and different directions of charge current flow will be presented along with estimates for the accumulated spin densities. Thermally induced effects will also be discussed. [1] Phys. Rev. Lett. 118, 077201 (2017), [2] Phys. Rev. Lett. 126, 127701 (2021).