Spin diffusion and torques in disordered antiferromagnets

TL;DR

This paper develops a drift-diffusion model for spin transport in disordered collinear bipartite antiferromagnets, analyzing spin transfer torques and the possibility of self-torque effects due to spin Hall phenomena.

Contribution

It introduces a quantum kinetic-based drift-diffusion framework for spin dynamics in antiferromagnets, including novel self-torque effects from intrinsic spin Hall effects.

Findings

Antiferromagnets can experience self-torque due to their own spin Hall effect.

The model describes spin accumulation and currents on each sublattice in diffusive regimes.

Spin transfer torques are analyzed in various heterostructures involving antiferromagnets.

Abstract

We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting in an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (ii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.