Planar Hall torque

TL;DR

This paper introduces a novel spin-orbit torque originating from planar Hall currents within the ferromagnetic layer, showing potential for efficient magnetic switching with unique symmetry and significant magnitude.

Contribution

It reports a new type of spin-orbit torque from planar Hall currents in ferromagnets, expanding understanding of torque mechanisms in magnetic bilayers.

Findings

Planar Hall torque can induce auto-oscillations of magnetization.

The torque exhibits biaxial symmetry in the plane.

Its magnitude is comparable to spin Hall torque.

Abstract

Spin-orbit torques in bilayers of ferromagnetic and nonmagnetic materials hold promise for energy efficient switching of magnetization in nonvolatile magnetic memories. Previously studied spin Hall and Rashba torques originate from spin-orbit interactions within the nonmagnetic material and at the bilayer interface, respectively. Here we report a spin-orbit torque that arises from planar Hall current in the ferromagnetic material of the bilayer and acts as either positive or negative magnetic damping. This planar Hall torque exhibits unusual biaxial symmetry in the plane defined by the applied electric field and the bilayer normal. The magnitude of the planar Hall torque is similar to that of the giant spin Hall torque and is large enough to excite auto-oscillations of the ferromagnetic layer magnetization.