We discuss the influence of a uniform current, j, on the
magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
ϵ(q) has a current-induced contribution proportional to
q⋅J, where J is the spin-current, and
predict that collective dynamics will be more strongly damped at finite 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≳109Acm−2. We discuss the relationship of this effect to
the spin-torque effects that alter magnetization dynamics in inhomogeneous
magnetic systems.Comment: 12 pages, 2 figure