Spin currents in magnetic films.

Spin currents injected into magnetic thin films may noticeably change the magnetization of the films. To describe this effect, exchange coupled Landau-Lifshitz equations for the local magnetization and the spin-polarized charge carriers are combined with transport equations for charge and spin currents. For steady state transport one obtains two different instability conditions. Both conditions are supported by recent experimental data on current induced magnetization reversal and spin-wave excitations. No second ferromagnetic layer is needed for excitations due to spin transfer.