J. Phys. IV France 07 (1997) C1-419-C1-420
Study of the Gyromagnetic Resonance Damping in Relaxing Rare Earth Substituted YGd2Fe5O12 GarnetsT. Taffary1, H. Pascard2, D. Autissier1 and F. Boust3
1 CEA-DAM BP. 12, 91680 Bruyères-le-Châtel, France
2 École Polytechnique, Laboratoire SESI, 91128 Palaiseau cedex, France
3 ONERA OM, BP. 72, 92322 Châtillon cedex, France
The influence of magnetic state (saturated or unsaturated states) on the gyromagnetic resonance damping in relaxing rare earth substituted Y1-xDyxGd2Fe5O12 garnets (with x=0;0.15;0.3;0.6) has been studied. The damping parameter α, as defined by Landau-Lifshitz equation, has been determined either by FMR at 10GHz (saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1GHz-10GHz band (unsaturated state). On the one hand, the damping parameter αsat has been calculated by fitting the FMR spectra of single crystals with the theoretical lorentzian shape. On the other hand, the damping parameter αunsat of polycrystals has been calculated using models which take into account the interaction between magnetic domains. In the fully magnetized state the introduction of relaxing rare earth (Dy) is found to increase significantly αsat values (from 0.02 to 0.3 when x varies from 0 to 0.6). On the contrary, the introduction of Dy hardly increases αunsat values. It appears that the difference between αsat and αunsat values stems not only from the interaction between magnetic domains but also from the modification of the damping in each magnetic domain owing to the presence of magnetic domain walls.
© EDP Sciences 1997