Theory of spin-Hall magnetoresistance in the AC (terahertz) regime

TL;DR

This paper develops a theoretical framework for spin-Hall magnetoresistance (SMR) in bilayers at terahertz frequencies, revealing singularities at magnon modes and potential for electric magnon spectroscopy.

Contribution

It introduces a comprehensive theory of SMR at high frequencies, linking it to magnon modes and spin transport in ferromagnet-normal metal bilayers.

Findings

SMR exhibits singularities at ferromagnetic spin-wave frequencies.

SMR magnitude changes with frequency due to magnonic contributions.

Potential for all-electric spectroscopy of magnon modes using SMR.

Abstract

In bilayers consisting of a normal metal (N) with spin-orbit coupling and a ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer torque, and the inverse spin-Hall effect gives a small correction to the in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance (SMR). We here present a theory of the SMR and the associated off-diagonal conductivity corrections for frequencies up to the terahertz regime. We show that the SMR signal has pronounced singularities at the spin-wave frequencies of F, which identifies it as a potential tool for all-electric spectroscopy of magnon modes. A systematic change of the magnitude of the SMR at lower frequencies is associated with the onset of a longitudinal magnonic contribution to spin transport across the F-N interface.