Anatomy of spin-orbit-torque-assisted magnetization dynamics in Co/Pt bilayers: Importance of the orbital torque

TL;DR

This study uses atomistic simulations to analyze the complex roles of spin and orbital moments in magnetization switching of Pt/Co bilayers, emphasizing the significance of orbital torques and interface interactions.

Contribution

It provides a quantitative, layer-resolved analysis of spin and orbital torques, highlighting the importance of orbital moments and interface effects in switching dynamics.

Findings

Orbital moments significantly contribute to field-like spin-orbit torque.

Induced Pt moments at the interface are crucial for switching behavior.

Layer-resolved model clarifies damping-like and field-like torque origins.

Abstract

Understanding the mechanism driving magnetization switching in spin-orbit-torque-assisted devices remains a subject of debate. While originally attributed to the spin Hall effect and spin Rashba-Edelstein effect, recent discoveries related to orbital moments induced by the orbital Hall effect and the orbital Rashba-Edelstein effect have added complexity to the comprehension of the switching process in non-magnet/ferromagnet bilayers. Addressing this challenge, we present a quantitative investigation of a Pt/Co bilayer by employing atomistic spin dynamics simulations, incorporating the proximity-induced moments of Pt, as well as electrically induced spin and orbital moments obtained from first-principles calculations. Our layer-resolved model elucidates the damping-like and field-like nature of the induced moments by separating them according to their even and odd magnetization dependence. In addition to demonstrating that a larger field-like spin-orbit torque contribution comes from previously disregarded induced orbital moments, our work highlights the necessity of considering interactions with Pt induced moments at the interface, as they contribute significantly to the switching dynamics.