Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal

Abstract

We discuss the influence of a uniform current, $\vec{j}$, on the magnetization dynamics of a ferromagnetic metal. We find that the magnon energy $\hat{I}\mu (\vec{q})$ has a current-induced contribution proportional to $\vec{q}\cdot \vec{\mathcal{J}}$, where $\vec{\mathcal{J}}$ is the spin-current, and predict that collective dynamics will be more strongly damped at finite $\vec{j}$. We obtain similar results for models with and without local moment participation in the magnetic order. For transition metal ferromagnets, we estimate that the uniform magnetic state will be destabilized for $j\gtrsim 10^9\mathrm{A}{\mathrm{cm}}^{-2}$. We discuss the relationship of this effect to the spin-torque effects that alter magnetization dynamics in inhomogeneous magnetic systems.

12 pages, 2 figures