Current-induced magnetization switching of exchange-biased NiO heterostructures characterized by spin-orbit torque

TL;DR

This study demonstrates deterministic current-induced magnetization switching in NiO heterostructures using spin-orbit torque, highlighting differences between W and Pt layers in efficiency and stability, without external magnetic fields.

Contribution

It provides a comprehensive analysis of spin-orbit torque-induced switching in NiO heterostructures, introducing an analytical model and comparing W and Pt layers for the first time.

Findings

W layers exhibit higher spin Hall angles than Pt.

Switching occurs deterministically with in-plane exchange bias.

W devices have lower critical current densities than Pt devices.

Abstract

In this work, we study magnetization switching induced by spin-orbit torque in W(Pt)/Co/NiO heterostructures with variable thickness of heavy-metal layers W and Pt, perpendicularly magnetized Co layer and an antiferromagnetic NiO layer. Using current-driven switching, magnetoresistance and anomalous Hall effect measurements, perpendicular and in-plane exchange bias field were determined. Several Hall-bar devices possessing in-plane exchange bias from both systems were selected and analyzed in relation to our analytical switching model of critical current density as a function of Pt and W thickness, resulting in estimation of effective spin Hall angle and perpendicular effective magnetic anisotropy. We demonstrate in both the Pt/Co/NiO and the W/Co/NiO systems the deterministic Co magnetization switching without external magnetic field which was replaced by in-plane exchange bias field. Moreover, we show that due to a higher effective spin Hall angle in W than in Pt-systems the relative difference between the resistance states in the magnetization current switching to difference between the resistance states in magnetic field switching determined by anomalous Hall effect ($\Delta R/\Delta R_{\text{AHE}}$) is about twice higher in W than Pt, while critical switching current density in W is one order lower than in Pt-devices. The current switching stability and training process is discussed in detail.