Spin-wave amplification and lasing driven by inhomogeneous spin transfer torques

TL;DR

This paper demonstrates that inhomogeneous spin transfer torques in ferromagnets can amplify and induce lasing of spin waves, potentially advancing magnonic devices for logic and data processing.

Contribution

It introduces a novel mechanism for spin-wave amplification and lasing driven by inhomogeneous spin transfer torques, with theoretical analysis of scattering and lasing conditions.

Findings

Inhomogeneous spin transfer torques amplify incoming spin waves.

Thermally occupied spin waves can be spontaneously amplified, leading to spin-wave lasing.

The results relate to black-hole laser analogies and have implications for magnonics.

Abstract

We show that an inhomogeneity in the spin-transfer torques in a metallic ferromagnet under suitable conditions strongly amplifies incoming spin waves. Moreover, at nonzero temperatures the incoming thermally occupied spin waves will be amplified such that the region with inhomogeneous spin transfer torques emits spin waves spontaneously, thus constituting a spin-wave laser. We determine the spin-wave scattering amplitudes for a simplified model and set-up, and show under which conditions the amplification and lasing occurs. Our results are interpreted in terms of a so-called black-hole laser, and could facilitate the field of magnonics, that aims to utilize spin waves in logic and data-processing devices.