Large Orbital Torque from Interfacial Spin-Vorticity Coupling in PtCo/Cu Heterostructures

The use of orbital torques to efficiently modulate magnetization is currently a central topic in orbitronics. In this Letter, we report the discovery of an unexpectedly large dampinglike torque efficiency per unit electric field in metallic PtCo/Cu heterostructures, with its maximum value being 2 (1) orders of magnitude higher than that in typical heavy-metal Ta (Pt) systems. Current-induced magnetization reversal experiments confirm the enhanced dampinglike torque efficiency, which increases significantly with the thickness of the Cu layer. We attribute this ultraefficient orbital torque to the interfacial vorticity of the drift velocity of conduction electrons, arising from the substantial resistivity difference between the Cu and PtCo layers. The remarkable dampinglike torque efficiency demonstrated in our Letter highlights the potential of interfacial vorticity in spin orbitronics, suggesting a promising new direction for future research in the field.