Magnetic and magneto-optical properties of rare-earth transition-metal alloys containing Gd, Tb, Fe, Co

Binary and ternary amorphous rare-earth transition-metal alloys of general composition RE1−x(Fe1−yCoy)x with RE=Gd, Tb and 0<x<1, 0≤y≤1 were prepared by evaporation. The saturation magnetization, uniaxial anisotropy, and Faraday rotation were investigated as a function of composition and temperature. Also, from the temperature-dependent measurements the compositional variation of the Curie temperature and the compensation temperature were determined. The experimental data have been analyzed in terms of the mean-field theory yielding spin values and effective exchange interaction energies. The compositional variation of the spin value was described by the environment model. The anisotropy data were fitted with a dipolar equation using the sublattice magnetizations inferred from the mean-field analysis. The magneto-optical effects are primarily caused by the transition metals. For the binaries GdFe and GdCo the compositional variation of the Kerr rotation typically peaks between 1000 and 1500 nm. The lowest magneto-optical effects for binary RE-Th alloys with respect to composition are reached at about x≊0.5 for T=4.2 K. The temperature dependence of the Faraday rotation can be well described in terms of the sublattice magnetizations.