Large dampinglike torque contribution originating from the orbital Rashba-Edelstein effect at a Pt/CoO interface

Current-induced spin-orbit torque (SOT) provides an efficient strategy for electrical manipulation of magnetism in spintronic devices. However, despite more than one decade of research for current-induced torque optimization, the charge-to-spin conversion efficiency and the resistivity in the spin-current source materials do not satisfy the requirement for next-generation low-consumption devices. Authors of recent theoretical works have predicted that an oxide or nitride interface can induce orbital angular momentum (OAM) accumulation through the orbital Rashba-Edelstein effect (OREE) and exert orbital torques to the adjacent magnetic layer. Here, we report on the remarkable dampinglike torque contribution from the OREE at the Pt/Co-O interface. In the Co/Co-O/Pt structures, the insertion of a thin natural-oxidized Co-O layer results in the sign reversal of SOT efficiency, suggesting the existence of a competing SOT source. In addition, the SOT efficiency and spin Hall magnetoresistance ratio in the Pt/Co structure were elevated significantly by introducing a Co-O underlayer. Anomalous SOT has also been observed in the Pt/Co/Co-O/Pt structures with perpendicular magnetic anisotropy by using the loop-shift technique and current-induced magnetization switching. After excluding the bulk contribution from the Co-O layer and its possible manipulation to the spin current from the Pt layer, we attribute this anomalous SOT origin to the OREE at the Co-O/Pt interface. In this paper, we not only provide a strategy for generating additional spin current for manipulating the SOT but also demonstrate an important clue toward microscopic understanding of how the out-of-equilibrium OAM interacts with the local magnetization.