The intrinsic damping mechanism in metals caused by incoherent scattering of itinerant electron-hole pair excitations by phonons and
magnons will be reviewed. The unique features of magnetic relaxations
in multilayers were studied by ferromagnetic resonance (FMR) using
magnetic single, Au-Fe-GaAs(001), and double layer
Au-Fe-Au-Fe-GaAs(001) structures prepared by molecular beam epitaxy.
The magnetic relaxation in single-layer films is described by the
Gilbert damping with no extrinsic contributions to the FMR linewidth.
These films provided an excellent opportunity to investigate nonlocal
damping. The main result of these studies is that ultrathin Fe films in
magnetic double layers acquire an additional interface Gilbert damping.
This is in agreement with recent predictions of nonlocal interface
damping which Is based on the transport of spin angular momentum
between the ferromagnetic layers. Measurements of the nonlocal Gilbert
damping offer a possibility to carry out quantitative studies of the
relaxation torques caused by nonlocal spin momentum transfer. Numerical
simulations of magnetization reversal and stationary precession for an
applied perpendicular current in Au-Fe-Au-Fe-GaAs(001) multilayers will
be shown.