Investigation of Partially Oxidized Cu Capping Effect on CoFeB/Pt/CuOx Multilayers by Electrical and Optical Methods

Orbital Hall effect in light metals has attracted attentions recently, but research on the orbital Rashba-Edelstein effect and its inverse effect is relatively limited. In this study, we experimentally demonstrate the existence of both effects in CoFeB/Pt/CuOx multilayers. By conducting spin Hall magnetoresistance (SMR) and anisotropic magneto resistance (AMR) measurements simultaneously and calculating the ratio between them, we rule out the current shunt effect and conclude the surface oxidized Cu film contributes to the generation of orbital Hall currents, and these orbital Hall currents exhibit the same polarization as the spin currents generated by Pt. Our argument is further substantiated by the THz emission measurements which show that the effective spin diffusion length in Pt increases from 3.57 nm to 4.37 nm with the addition of CuOx. Our work provides further evidence to the hypothesis of interface related charge-orbital interconversion.