Direct optical observation of spin accumulation at nonmagnetic metal/oxide interface

We report the direct observation of uniform in-plane spin accumulation at room temperature by magneto optical Kerr effect, at the interface formed between nonmagnetic metal (Cu, Ag) and oxide (Bi₂O₃). Recent reports show spin to charge conversion at these interfaces suggesting the presence of Rashba like spin orbit coupling (SOC). The formation of spin accumulation is the result of current induced spin polarization at our interfaces (direct Rashba–Edelstein effect), without external magnetic field or proximity to ferromagnetic materials. We observe opposite orientation of spin accumulation at Cu/Bi₂O₃ and Ag/Bi₂O₃ interfaces reflecting their opposite sign of Rashba SOC (Rashba parameter). Moreover, estimation of spin accumulation from values of Rashba parameters obtained by independent spin pumping measurements, agrees well with the difference in amplitude of our normalized Kerr signals for Cu/Bi₂O₃ and Ag/Bi₂O₃ interfaces. Uniform in-plane spin accumulation due to Rashba-Edelstein effect can be applied for spin filter devices and efficient driving force for magnetization switching.