Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with vertical composition gradient

TL;DR

This paper demonstrates a method for deterministic, bias-field-free switching of perpendicular magnetization in a ferrimagnetic layer with a vertical composition gradient, leveraging intrinsic spin-orbit torques and gradient-driven Dzyaloshinskii-Moriya interaction.

Contribution

It introduces a novel vertical composition gradient in a ferrimagnetic layer to achieve bias-free SOT switching, eliminating the need for external magnetic fields or structural asymmetry.

Findings

Successful demonstration of bias-free SOT switching in a single perpendicular CoTb layer.

Vertical composition gradient induces strong intrinsic SOTs and g-DMI.

Micromagnetic simulations confirm the role of g-DMI in deterministic switching.

Abstract

Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices. To be deterministic, however, switching of perpendicularly magnetized materials by SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do so involve the application of an in-plane bias magnetic field, or incorporation of in-plane structural asymmetry in the device, both of which can be difficult to implement in practical applications. Here, we reported bias-field-free SOT switching in a single perpendicular CoTb layer with an engineered vertical composition gradient. The vertical structural inversion asymmetry induces strong intrinsic SOTs and a gradient-driven Dzyaloshinskii-Moriya interaction (g-DMI), which breaks the in-plane symmetry during the switching process. Micromagnetic simulations are in agreement with experimental results, and elucidate the role of g-DMI in the deterministic switching. This bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI provides a strategy for efficient and compact SOT device design.