In-situ study of oxygen exposure effect on spin-orbit torque in Pt/Co bilayers in ultrahigh vacuum

TL;DR

This study investigates how oxygen exposure influences spin-orbit torque in Pt/Co bilayers, revealing a modest increase linked to surface-adsorbed oxygen and the Rashba-Edelstein effect, with implications for spintronic device optimization.

Contribution

It provides in-situ experimental evidence and ab initio calculations clarifying the role of oxygen in modulating spin-orbit torque in Pt/Co bilayers.

Findings

Oxygen exposure increases spin-orbit torque but less than previously reported.

MgO capping layer also enhances spin-orbit torque.

Enhanced Rashba-Edelstein effect due to surface oxygen explains the increase.

Abstract

Oxygen incorporation has been reported to increase the current-induced spin-orbit torque in ferromagnetic heterostructures, but the underlying mechanism is still under active debate. Here, we report on an in-situ study of the oxygen exposure effect on spin-orbit torque in Pt/Co bilayers via controlled oxygen exposure, Co and Mg deposition, and electrical measurements in ultrahigh vacuum. We show that the oxygen exposure on Pt/Co indeed leads to an increase of spin-orbit torque, but the enhancement is not as large as those reported previously. Similar enhancement of spin-orbit torque is also observed after the deposition of an MgO capping layer. The results of ab initio calculations on the Rashba splitting of Pt/Co and Pt/Co/O suggest that the enhancement is due to enhanced Rashba-Edelstein effect by surface-adsorbed oxygen. Our findings shed some light on the varying roles of oxygen in modifying the spin torque efficiency reported previously.