Mitigation of Gilbert Damping in the CoFe/CuOx Orbital Torque System

TL;DR

This study demonstrates that partially-oxidized 3d metals like CuOx can produce strong orbital torques with minimal increase in magnetic damping, offering new ways to excite magnetization dynamics efficiently.

Contribution

It reveals that CuOx can generate orbital torque comparable to Pt without significant damping increase, unlike traditional spin sinks.

Findings

Orbital torque efficiency in CoFe/CuOx is comparable to CoFe/Pt.

Damping increase in CoFe/CuOx is minimal ({ extless}0.002).

Lack of efficient spin sink in CuOx explains the nonreciprocal damping and torque relationship.

Abstract

Charge-spin interconversion processes underpin the generation of spin-orbit torques in magnetic/nonmagnetic bilayers. However, efficient sources of spin currents such as 5d metals are also efficient spin sinks, resulting in a large increase of magnetic damping. Here we show that a partially-oxidized 3d metal can generate a strong orbital torque without a significant increase in damping. Measurements of the torque efficiency {\xi} and Gilbert damping {\alpha} in CoFe/CuOx and CoFe/Pt indicate that {\xi} is comparable. The increase in damping relative to a single CoFe layer is {\Delta}{\alpha}<0.002 in CoFe/CuOx and {\Delta}{\alpha} ~ 0.005 - 0.02 in CoFe/Pt, depending on CoFe thickness. We ascribe the nonreciprocal relationship between {\Delta}{\alpha} and {\xi} in CoFe/CuOx to the small orbital-to-spin current ratio generated by magnetic resonance in CoFe and the lack of an efficient spin sink in CuOx. Our findings provide new perspectives on the efficient excitation of magnetization dynamics via the orbital torque.