Boosting charge-to-spin current conversion using orbital Hall effect of Ru with opposing spin–orbit correlated interlayers

Power-efficient spintronics has long been pursued for scalable and commercially viable devices. While significant progress has been made using materials that exhibit the spin Hall effect (SHE), the orbital Hall effect (OHE) has recently emerged as a promising alternative. Unlike the SHE, the OHE does not require strong spin–orbit coupling (SOC), making it accessible in light metals. Ru, in particular, stands out due to its low resistivity and high orbital conductivity. However, the orbital current (IOH) generated by OHE must be converted into spin current (ISH) to exert torque on the magnetic moments of ferromagnets, a process governed by the spin–orbit correlation in adjacent layers. In this work, we investigate the IOH→ISH conversion efficiency using Ru combined with Pt and W interlayers. We evaluate damping-like torque efficiency (ξDL), reflecting on the IOH→ISH efficiency of Pt and W interlayers. Incorporating Ru enhances ξDL compared to conventional Pt/Co bilayers. Placing Pt and W on either side of the Co layer, which has opposite spin–orbit correlations, enabled a 2.3-fold enhanced ξDL. Furthermore, the current density required for magnetization switching was reduced, enabling energy-efficient magnetization control. These results demonstrate a viable pathway to optimizing orbital torque and advancing the design of power-efficient spintronic devices.