Spin-wave emitting diodes and spin diffusion in magnetic multilayers

When a dc current traverses a magnetic multilayer, a spontaneous precession of the magnetization is predicted to arise. In the present work, we discuss three different configurations for this device. We show that the multilayer must not exhibit complete mirror symmetry with respect to the median plane of the precessing layer. Also, we solve the Valet-Fert spin-diffusion equations in the various layers. The results lead to certain optimum values for the layer thicknesses and for the conduction-electron spin-relaxation time in some layers. Finally, we propose an alternate mechanism to "pump" the conduction-electron spins.