Field-free spin-orbit torque switching through domain wall motion

TL;DR

This paper demonstrates field-free deterministic spin-orbit torque switching in a multilayer magnetic heterostructure by using domain wall motion, eliminating the need for an external in-plane magnetic field.

Contribution

It introduces a multilayer stack with an in-plane magnetized layer enabling field-free SOT switching, highlighting the role of Neel coupling over stray fields.

Findings

Switching is dominated by domain nucleation and domain wall motion.

Deterministic switching cannot be explained by stray fields alone.

Neel coupling plays a key role in achieving field-free switching.

Abstract

Deterministic current-induced spin-orbit torque (SOT) switching of magnetization in a heavy transition metal/ferromagnetic metal/oxide magnetic heterostructure with the ferromagnetic layer being perpendicularly-magnetized typically requires an externally-applied in-plane field to break the switching symmetry. We show that by inserting an in-plane magnetized ferromagnetic layer CoFeB underneath the conventional W/CoFeB/MgO SOT heterostructure, deterministic SOT switching of the perpendicularly-magnetized top CoFeB layer can be realized without the need of in-plane bias field. Kerr imaging study further unveils that the observed switching is mainly dominated by domain nucleation and domain wall motion, which might limit the potentiality of using this type of multilayer stack design for nanoscale SOT-MRAM application. Comparison of the experimental switching behavior with micromagnetic simulations reveals that the deterministic switching in our devices cannot be explained by the stray field contribution of the in-plane magnetized layer, and the roughness-caused N\'eel coupling effect might play a more important role in achieving the observed field-free deterministic switching.