Redefinition of spin Hall magnetoresistance

TL;DR

This paper introduces a new multi-conduction-channel model for spin Hall magnetoresistance (SMR), showing that SMR can occur without magnetic insulators and is driven by electron scattering at interfaces, with a significant increase in effect observed in specific layered samples.

Contribution

The study redefines the micromechanism of SMR using a multi-channel approach, highlighting the role of electron scattering and demonstrating SMR in non-magnetic insulator systems.

Findings

SMR can be observed without magnetic insulators.

The model predicts typical resistance relationships in SMR.

Intrinsic SMR varies with magnetic field orientation in the XZ plane.

Abstract

Using a multi-conduction-channel model, we redefined the micromechanism of spin Hall magnetoresistance (SMR). Four conduction channels are created by spin accumulation of nonpolarized electron flow at top, bottom, left and right interfaces of the film sample, which corresponds to different resistance states of polarized electron flow with various spin directions relative to the applied magnetic field ($\mathbf{H}$), and brings about the SMR effect finally. The magnetic insulator layer, such as yttrium iron garnet (YIG), is not a requisite for the observation of SMR. Instead, the SMR effect is perfectly realized, with an order of magnitude increase, in the sample with a discontinuous layer of isolated-Co$_2$FeAl (0.3 nm) grains covered by 2.5-nm-thick Pt layer on MgO substrate. The model intuitively gives the typical relationship of SMR effect, i.e. $\rho_{\parallel}\approx\rho_{\bot}>\rho_{T}$, where $\rho_{\bot}$, $\rho_{\parallel}$ and $\rho_{T}$ are longitudinal reisitivities with applied magnetic field ($\mathbf{H}$) direction perpendicular to the current direction out of plane (as Z direction), parallel with and perpendicular to it in plane (as X and Y direction), respectively. Our research reveals that the scattering between polarized and nonpolarized conduction electrons is the origin of SMR, and the intrinsic SMR is not constant when $\mathbf{H}$ direction rotates in XZ plane, which is distinct from that in the reported SMR mechanism.