Influence of a uniform current on collective magnetization dynamics in a ferromagnetic metal

We discuss the influence of a uniform current $\overrightarrow{j}$ on the magnetization dynamics of a ferromagnetic metal. We find that the magnon energy $\epsilon \left(\overrightarrow{q}\right)$ has a current-induced contribution proportional to $\overrightarrow{q}\cdot \mathcal{J}\to ,$ where $\mathcal{J}\to$ is the spin current, and predict that collective dynamics will be more strongly damped at finite $\overrightarrow{j}.$ 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 $j\gtrsim {10}^9{\mathrm{A}\mathrm{}\mathrm{cm}}^{-2}.$ We discuss the relationship of this effect to the spin-torque effects that alter magnetization dynamics in inhomogeneous magnetic systems.