Switching of perpendicular magnetization via orbital-current-induced torque from light metal Ru

Orbital torque (OT) harnesses orbital currents to electrically encode spin states, offering a promising route toward low-power spintronic devices. However, the microscopic mechanisms governing OT efficiency remain elusive. Here, we employ Ru, a light metal possessing positive spin and orbital Hall conductivities, as an orbital source to switch perpendicularly magnetized Co/Pt3 multilayers with a negative orbital-to-spin conversion coefficient. This configuration enables a clear separation between OT and conventional spin–orbit torque. We find that the OT efficiency decreases monotonically with increasing Ru thickness, confirming an interfacial rather than bulk origin of the orbital current. Notably, robust magnetization switching persists even for a Ru thickness of only 1 nm, achieving a critical switching current density of 1.9 × 107 A/cm2, nearly half that of the heavy-metal Pt reference. These findings not only elucidate the physical mechanism of OT but also establish key design principles for the development of energy-efficient orbitronic memory devices.