Large interfacial Rashba interaction and giant spin-orbit torques in atomically thin metallic heterostructures

TL;DR

This paper demonstrates that inserting a thin Al layer at the interface of ultrathin Co ferromagnets significantly enhances spin-orbit torques due to large Rashba interactions, enabling more efficient magnetization switching.

Contribution

It reveals a giant interfacial Rashba effect in atomically thin metallic heterostructures, leading to enhanced spin-orbit torques not previously observed in metallic interfaces.

Findings

Large field-like torque ratio (~2.5) with Al insertion

Giant Rashba interaction at Co|Al interface

Reduced critical current for magnetization switching

Abstract

The ability of spin-orbit interactions to convert charge current into spin current, most often in the bulk of heavy metal thin films, has been the hallmark of spintronics in the last decade. In this study, we demonstrate how the insertion of light metal element interface profoundly affects both the nature of spin-orbit torque and its efficiency in terms of damping-like ($H_{\text{DL}}$) and field-like ($H_{\text{FL}}$) effective fields in ultrathin Co ferromagnet. Indeed, we measure unexpectedly large $H_{\text{FL}}$/$H_{\text{DL}}$ ratio ($\sim$2.5) upon inserting a 1.4 nm thin Al layer in Pt|Co|Al|Pt as compared to a similar stacking including Cu instead of Al. From our modelling, these results strongly evidence the presence of large Rashba interaction at Co|Al interface producing a giant $H_{\text{FL}}$, which was not expected from a metallic interface. The occurrence of such enhanced torques from an interfacial origin is further validated by demonstrating current-induced magnetization reversal showing a significant decrease of the critical current for switching.