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

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

Work at the University of Texas was supported by the Welch Foundation and by the National Science Foundation under Grants Nos. DMR-0210383 and DMR-0115947. Work at University of Alicante was supported by Ramón y Cajal Program, Ministerio de Ciencia y Tecnología, Grants Nos. MAT2003-08109-C02-01 and UA/GRE03-15.