Suppression of the field-like torque for efficient magnetization switching in a spin–orbit ferromagnet

Abstract

Spin–orbit torque magnetization switching is an efficient method to control magnetization. In perpendicularly magnetized films, two types of spin–orbit torque are induced by driving a current: a damping-like torque and a field-like torque. The damping-like torque assists magnetization switching, but a large field-like torque pushes the magnetization towards the in-plane direction, resulting in a larger critical switching current density and making deterministic switching challenging. Control of the field-like torque strength is difficult because it is intrinsic to the material system used. Here, we show that the field-like term can be suppressed in a spin–orbit ferromagnetic single layer of (Ga,Mn)As by a current-induced Oersted field due to its non-uniform current distribution, making the damping-like torque term (the result of strong Dresselhaus spin–orbit coupling) dominant. The Oersted field can be controlled by the film thickness, resulting in an extremely low switching current density of 4.6 × 104 A cm–2. This strategy can thus provide an efficient approach to spin–orbit torque magnetization switching. A spin–orbit ferromagnetic single layer of (Ga,Mn)As can have a magnetization switching current density as low as 4.6 × 104 A cm−2 by suppressing the field-like torque via control of the current direction and film thickness.