Role of spin current in magnetic relaxations of metallic multilayer films

In our recent studies the relaxation processes were investigated by ferromagnetic resonance (FMR) using magnetic single, Au/Fe/GaAs(0 0 1), and double layer, Au/Fe/Au/Fe/GaAs(0 0 1), structures prepared by molecular beam epitaxy (MBE). Single and double layer structures were grown on (4x6) reconstructed GaAs(0 0 1) templates. The samples have high crystalline quality with the magnetic properties corresponding to bulk Fe, only modified by interface anisotropies. The magnetic relaxation in these structures is well described by Gilbert damping with no extrinsic contributions to the FMR line width. These structures provide an excellent opportunity to investigate non-local damping which is caused by spin transport across a non-magnetic spacer. In the double layer structures thin Fe layers were separated from a second thick Fe layer of 40 monolayer (ML) thickness by a 40 ML thick Au(0 0 1) spacer. The main result of these studies is that the ultrathin Fe films in magnetic double layers acquire an additional Gilbert damping. The additional FMR line width followed an inverse dependence on the Fe film thickness which is expected for interface damping. The spin pump model will be discussed and it will be shown that it is closely related to the dynamic part of interlayer exchange coupling