Non-equilibrium Spin Waves in Paramagnetic Metals

TL;DR

This paper theoretically investigates how exchange interactions influence non-equilibrium spin waves in disordered paramagnetic metals, revealing conditions for their propagation, damping, and potential electromagnetic field amplification near phase transitions.

Contribution

It introduces a theoretical framework for understanding non-equilibrium spin waves in paramagnetic metals, highlighting the effects of exchange interaction and phase transition proximity.

Findings

Spin wave spectrum becomes negative near phase transition.

Damping is small when exchange energy exceeds inverse mean free time.

Spin wave propagation is suppressed in the opposite limit.

Abstract

We theoretically study the effect of exchange interaction on the non-equilibrium spin waves in disordered paramagnetic metals under the spin injection condition. We show that the gapless spectrum of spin waves, describing the spin precession in the absence of the applied magnetic field, changes sign to negative on the paramagnetic side near the ferromagnet - paramagnet phase transition. The damping of spin waves is small in the limit when electron-electron exchange energy is larger than the inverse electron mean free time, while in the opposite limit the propagation of spin waves is strongly suppressed. We discuss the amplification of the electromagnetic field by the non-equilibrium spin waves.