Spin pumping by a moving domain wall at the interface of an antiferromagnetic insulator and a two-dimensional metal

TL;DR

This paper investigates how a moving domain wall at an antiferromagnetic insulator and 2D metal interface can pump spin polarization into the metal, revealing effects dependent on interface interactions, electron scattering, and Fermi surface geometry.

Contribution

It provides a theoretical analysis of spin pumping by a moving domain wall at an AFMI/2D metal interface using Keldysh Green's functions, highlighting second-order effects and geometric sensitivities.

Findings

Spin pumping occurs in second order with respect to exchange interaction.

Pumped polarization can surpass first-order Pauli magnetism effects at weak spin relaxation.

Spin polarization distribution is asymmetric and extends beyond the domain wall width.

Abstract

A domain wall (DW) which moves parallel to a magnetically compensated interface between an antiferromagnetic insulator (AFMI) and a two-dimensional (2D) metal can pump spin polarization into the metal. It is assumed that localized spins of a collinear AFMI interact with itinerant electrons through their exchange interaction on the interface. We employed the formalism of Keldysh Green's functions for electrons which experience potential and spin-orbit scattering on random impurities. This formalism allows a unified analysis of spin pumping, spin diffusion and spin relaxation effects on a 2D electron gas. It is shown that the pumping of a nonstaggered magnetization into the metal film takes place in the second order with respect to the interface exchange interaction. At sufficiently weak spin relaxation this pumping effect can be much stronger than the first-order effect of the Pauli magnetism which is produced by the small nonstaggered exchange field of the DW. It is shown that the pumped polarization is sensitive to the geometry of the electron's Fermi surface and increases when the wave vector of the staggered magnetization approaches the nesting vector of the Fermi surface. In a disordered diffusive electron gas the induced spin polarization follows the motion of the domain wall. It is distributed asymmetrically around the DW over a distance which can be much larger than the DW width.