Observation of spin-orbit magnetoresistance in CoFeB/heavy metal/MgO with existence of both spin Hall effect and Edelstein effect

TL;DR

This study observes spin-orbit magnetoresistance in CoFeB/heavy metal/MgO systems, revealing contributions from both spin Hall and Edelstein effects, and provides a theoretical model to explain the experimental results.

Contribution

It demonstrates the existence of spin-orbit magnetoresistance linked to both spin Hall and Edelstein effects at the HM/MgO interface, supported by theoretical calculations.

Findings

Identification of a second MR peak around 1-2 nm HM thickness.

Evidence that SOMR originates from spin-orbit coupling at the HM/MgO interface.

Theoretical explanation of two MR peaks from spin Hall and Edelstein effects.

Abstract

In this paper, we report the observation of spin-orbit magnetoresistance (SOMR) in ferromagnetic metal/heavy metal/MgO system. We measure the magnetoresistance as the function of the thickness of heavy metal (HM) for CoFeB/HM/MgO and CoFeB/HM films where HM = Pt and Ta. Besides the conventional spin Hall magnetoresistance (SMR) peak, the evidence of the SOMR is indicated by another peak of the MR ratio when the thickness of HM is around 1 ~ 2 nm for CoFeB/HM/MgO films, which is absent for CoFeB/HM films. We speculate the SOMR observed in our experiment originates from the spin-orbit coupling at the HM/MgO interface. We give the boundary conditions of our samples and calculate the theoretical magnetoresistance based on spin diffusion equation. Based on the theoretical results, we can explain the two peaks we observe separately comes from the spin current generated by spin Hall effect and by Edelstein effect.