Ferromagnetic resonance damping in garnets: comparison between saturated and unsaturated states

The influence of magnetic state (saturated or unsaturated states) on the ferromagnetic resonance damping in relaxing rare earth substituted Y/sub 1-x/RE/sub x/Gd/sub 2/Fe/sub 5/O/sub 12/ garnets (with RE=Dy Ho, Tb and x=0;0.15;0.3;0.6) has been studied. The damping parameter a, as defined by Landau-Lifshitz equation, has been determined either by FMR at 10 GHz (/spl alpha//sub sat/ for saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1 GHz-10 GHz band (/spl alpha//sub unsat/ for unsaturated state). In the saturated state the introduction of relaxing rare earth is found to increase significantly /spl alpha//sub sat/ values by more than one order of magnitude. On the contrary, although /spl alpha//sub unsat/ values also increase with rare earth concentration they stay in the same order of magnitude. It appears that /spl alpha//sub unsat/ is controlled either by the magnetic disorder introduced via the domain and domain wall structure or by the rare earth concentration.