Drastic emergence of huge negative spin-transfer torque in atomically thin Co layers

TL;DR

This paper reveals a significantly enhanced negative nonadiabatic spin-transfer torque in atomically thin Co layers, which dominates over spin-orbit torque and causes domain wall motion opposite to traditional predictions, opening new avenues for spintronic device efficiency.

Contribution

It uncovers a large negative nonadiabatic spin-transfer torque in ultra-thin Co films, challenging existing models and suggesting a new mechanism for domain wall motion in spintronics.

Findings

Discovery of a large negative nonadiabatic STT in thin Co layers.

The new force exceeds the spin-orbit torque in magnitude.

Domain walls move along the current direction due to this force.

Abstract

Current-induced domain wall (DW) motion has drawn great attention in the last decades as the key operational principle of emerging magnetic memory devices. As the major driving force of the current-induced DW motion, the spin-orbit torque (SOT) on chiral DWs has been proposed and extensively studied nowadays. However, we demonstrate here that there exists another driving force, which is larger than the SOT in ultra-thin Co films. Moreover, the direction of the present force is found to be opposite to the prediction of the spin-transfer torque (STT), resulting in the DW motion along the current direction. The symmetry of the force and its peculiar dependence on the DW structure suggest that the present force is, most likely, attributed to considerable enhancement of the nonadiabatic STT with a negative spin polarization in atomically thin Co layers. These findings open a new pathway to enhance the overall spin torque efficiency-the critical parameter in emerging spintronic devices.