Current driven spin-wave instability triggered by the anomalous Hall effect

TL;DR

This paper investigates how strong electric currents, influenced by the anomalous Hall effect, can induce a spin-wave instability by reducing damping and causing exponential growth of spin-wave amplitudes.

Contribution

It introduces a new mechanism for spin-wave instability driven by the anomalous Hall effect, which can occur at lower currents than traditional spin-torque methods.

Findings

Critical current for instability is mainly determined by the anomalous Hall effect.

Spin-wave damping can be reduced and even become negative under strong currents.

The instability leads to exponential growth of spin-wave amplitudes.

Abstract

We studied the effect of strong electric current on spin waves interacting relativistically with the current. The spin-wave spectrum is calculated at arbitrary direction of the wave vector. It is shown that the alternating Hall current generated by the alternating magnetic moment of the spin waves, reduces the spin-wave damping. At strong enough unpolarized dc current the damping changes sign, and the spin-wave amplitude starts to increase exponentially fast with time. The critical current for the spin-wave instability is determined mainly by the anomalous Hall effect, and can be much smaller than that for the spin-torque mechanism of instability.