Joint action of spin-transfer and spin-injection torques in ferromagnetic junctions

We consider theoretically a current flowing perpendicular to interfaces of a spin-valve type ferromagnetic metallic junction. For the first time a simultaneous action of the two current effects is investigated, namely, the nonequilibrium longitudinal spin injection and the transverse spin surface torque. Dispersion relations for fluctuations are derived and solved under the proper boundary conditions. Joint action of the two effects mentioned lowers the instability threshold, its typical value being 1 x 10(6)-3 x 10(7) A/cm(2). Spin wave excitations may soften near the threshold. A nonlinear problem is solved about steady state arising due to instability development.