Spin relaxation processes in metallic magnetic nanostructures are reviewed. First a brief review of the phenomenology of magnetic damping
is presented using the Landau Lifshitz Gilbert (LLG) equations of
motion. It is shown that the Gilbert damping in bulk metallic layers is
caused by the spin orbit interaction and itinerant character of 3d and
4s-p electrons. Spin dynamics in magnetic nanostructures acquires an
additional nonlocal damping. This means that a part of the magnetic
damping is not given by the local Gilbert damping but arises from the
proximity to other layers. Spin pumping and spin sink concepts will be
introduced and used to describe the interface nonlocal Gilbert damping
in magnetic multilayers. The modified LLG equation of motion in
magnetic multilayers will be introduced and tested against the
ferromagnetic resonance (FMR) data around the accidental crossover of
FMR fields. The spin pumping theory will be compared to the early
theories introduced in the 1970s for the interpretation of transmission
electron spin resonance (TESR) measurements across ferromagnet/normal
metal sandwiches.