  Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
"spin-pumping" and the "breathing Fermi-surface" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.
