Spin transfer torques and spin-dependent transport in a metallic F/AF/N tunneling junction

TL;DR

This paper develops microscopic formulas for spin-dependent transport and torques in a ferromagnetic-antiferromagnetic-normal metal tunneling junction, revealing unique mechanisms and regimes relevant for spintronics applications.

Contribution

It introduces new formulas for spin torques and transport in F/AF/N junctions, highlighting unconventional damping-like torque and antiferromagnetic transport channels.

Findings

Unconventional damping-like torque can be comparable to conventional torque.

Antiferromagnetic sublattice structure enables unique electron transport channels.

Charge and spin currents depend on the relative orientation of magnetic vectors.

Abstract

We study spin-dependent electron transport through a ferromagnetic-antiferromagnetic-normal metal tunneling junction subject to a voltage or temperature bias, in the absence of spin-orbit coupling. We derive microscopic formulas for various types of spin torque acting on the antiferromagnet as well as for charge and spin currents flowing through the junction. The obtained results are applicable in the limit of slow magnetization dynamics. We identify a parameter regime in which an unconventional damping-like torque can become comparable in magnitude to the equivalent of the conventional Slonczewski's torque generalized to antiferromagnets. Moreover, we show that the antiferromagnetic sublattice structure opens up a channel of electron transport which does not have a ferromagnetic analogue and that this mechanism leads to a pronounced field-like torque. Both charge conductance and spin current transmission through the junction depend on the relative orientation of the ferromagnetic and the antiferromagnetic vectors (order parameters). The obtained formulas for charge and spin currents allow us to identify the microscopic mechanisms responsible for this angular dependence and to assess the efficiency of an antiferromagnetic metal acting as a spin current polarizer.