The Central Role of Tilted Anisotropy for Field-Free Spin-Orbit Torque Switching of Perpendicular Magnetization

TL;DR

This paper reveals that tilted magnetic anisotropy in Pt-based heterostructures enables deterministic, field-free spin-orbit torque switching of perpendicular magnetization, emphasizing the importance of growth-induced anisotropy in magnetic memory devices.

Contribution

It demonstrates that growth-dependent tilted anisotropy enables field-free SOT switching, highlighting a previously neglected factor in magnetic anisotropy control.

Findings

Tilted anisotropy controls field-free switching.

Switching exhibits conventional SHE-like torque features.

Effective field dependence on current density is non-linear.

Abstract

The discovery of efficient magnetization switching activated by the spin Hall effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic random-access memory (MRAM) research and development. However, for systems with perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by the necessity of a longitudinal magnetic field to break the magnetic symmetry to achieve deterministic switching. In this work, we first demonstrate that a robust and tunable field-free current-driven SOT switching of perpendicular magnetization can be controlled by the growth protocol in Pt-based magnetic heterostructures. It is further elucidated that such growth-dependent symmetry breaking is originated from the laterally tilted magnetic anisotropy of the ferromagnetic layer with PMA, which has been largely neglected in previous studies and its critical role should be re-focused. We show by both experiments and simulations that in a PMA system with tilted anisotropy, the deterministic field-free switching possesses a conventional SHE-induced damping-like torque feature and the resulting current-induced effective field has a non-linear dependence on the applied current density, which could be potentially misattributed to an unconventional SOT origin.