Abstract
Ferromagnetic resonance measurements of the magnetic anisotropy and resonance linewidth are reported for single-crystal specimens of the cubic Laves-phase intermetallic compound GdAl2 and for RxGd1-xAl2 where R is a heavy rare-earth ion. The doping levels of the samples were: for R=Tb, x=0.0025, 0.01, 0.02, 0.05; for R=Dy, x=0.02; for R=Ho, x=0.02; for R=Er, x=0.01, 0.03. Microwave frequencies close to 9.3, 14.3 and 17.3 GHz were employed. The anisotropy fields HK(100) and Hk(111) in the two principal crystallographic directions are reported for temperatures that range from 6 to 150K. Single-ion theory for the anisotropy at 0K, with crystal-field and exchange-field parameters taken from the literature, gives quite close agreement with experiment for Tb-doped samples, fair agreement for Er doping and disagreement for Dy and Ho. Doping causes a modest increase in the linewidth of resonance but this is much less severe than is observed for the substitution of similar amounts of the R ions in insulating ferromagnetics. Neither of the two models that have been employed to explain the observations in these insulating samples is successful in explaining the behaviour of the linewidth in the intermetallics and this is invoked as evidence that the R ions relax very much more rapidly in these latter than in the insulators. The linewidth passes through a minimum close to the Curie point.