Spin-orbit torques and spin accumulation in FePt/Pt and Co/Cu thin films from first principles: the role of impurities

TL;DR

This study uses first-principles calculations to analyze how impurities and temperature-related effects influence spin-orbit torques and spin accumulation in FePt/Pt and Co/Cu bilayers, revealing sensitive dependence on defect distribution and impurity type.

Contribution

It provides a detailed first-principles analysis of impurity effects on spin-orbit phenomena in bilayers, highlighting the importance of defect distribution and quasiparticle broadening.

Findings

Spin accumulation and torques depend on impurity distribution in FePt/Pt.

Impurity type significantly affects spin phenomena in Co/Cu bilayers.

Small quasiparticle broadening can drastically alter spin effects.

Abstract

Using the Boltzmann formalism based on the first principles electronic structure and scattering rates, we investigate the current-induced spin accumulation and spin-orbit torques in FePt/Pt and Co/Cu bilayers in the presence of substitutional impurities. In FePt/Pt bilayers we consider the effect of intermixing of Fe and Pt atoms in the FePt layer, and find a crucial dependence of spin accumulation and spin-orbit torques on the details of the distribution of these defects. In Co/Cu bilayers we predict that the magnitude and sign of the spin-orbit torque and spin accumulation depend very sensitively on the type of the impurities used to dope the Cu substrate. Moreover, simultaneously with impurity-driven scattering we consider the effect of an additional constant quasiparticle broadening of the states at the Fermi surface to simulate phonon scattering at room temperature, and discover that even a small broadening of the order of 25 meV can drastically influence the magnitude of the considered effects. We explain our findings based on the analysis of the complex interplay of several competing Fermi surface contributions to the spin accumulation and spin-orbit torques in these structurally and chemically non-uniform systems.