Ferromagnetic resonance relaxation in reaction milled and annealed Fe-Zn nanocomposites

SQUID magnetization measurements and ferromagnetic resonance experiments have been performed at 9.77 GHz on reaction milled and subsequently annealed nanocomposites of iron particles in a ZnO matrix. The dominant contribution to the temperature and time dependence of the observed linewidth of 2.2 to 3.2 kOe arises from the spatial inhomogeneity in shape, size and interaction fields of the system. Further linewidth contributions from stress, magnetization changes, surface reconstruction are discussed. The Gilbert relaxation constant alpha is decreasing with annealing temperature from 0.45 to 0.33 at 304 C.