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.

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Amorphous rare-earth transition-metal alloys of composition REl−xTMx with RE=Dy, Ho; TM=Fe,Co and 0<x<1 and Dyl−x(Fe,Co)x were prepared by evaporation. The saturation magnetization, uniaxial anisotropy, coercivity, and Faraday rotation were investigated as a function of composition and temperature. Also, the spectral variation of the Kerr rotation was measured. The magnetization data indicate a strong dispersion of the RE moments due to randomly oriented local crystal field axes. The strong turndown of the Curie temperature for the Fe-rich alloys suggests that an additional dispersion is present in the Fe subnetwork. The mean field theory was used to analyze the temperature variation of the magnetization yielding smaller TM spin values and exchange coupling constants as compared with those of the Gd and Tb analogs. The uniaxial anisotropy constant Ku for Dy-Co based alloys was found to vary with the square of the Dy subnetwork magnetization as predicted by the random single-ion theory. The anisotropy of Dy-Fe and Ho based alloys require additionally dipolar terms to account for the measured temperature dependence of Ku. The coercive field Hc follows a relation Hc ∼ K1.5u/Ms. The magneto-optical effects are primarily caused by the transition metals and therefore their compositional, temperature, and spectral dependence correspond to that of their Gd and Tb analogs. Optical recording experiments on Dy-FeCo disks yield good write and erase sensitivities and carrier-to-noise ratios up to 60 dB which are comparable to those of GdTb-Fe and Tb-FeCo disks.

Garnet films of composition R3−x−yPrxBiyFe5O12 with R=Lu, Y, and 0≤x≤1.8, 0≤y≤1.7 have been grown from different melt compositions and under various growth conditions onto substituted gadolinium gallium garnet substrates with (100), (110), (111), and (211) orientation. The dependence on composition and temperature of the saturation magnetization Ms, the uniaxial anisotropy constant Ku, the Faraday rotation θF, and the Faraday ellipticity ψF, have been investigated. The change of Ms as compared to that of Y3Fe5O12 is essentially associated with the alignment of the Pr moment parallel to the net iron moment and the increase of the Curie temperature originating mainly from the bismuth. However, both contributions are negligible in the room-temperature range. The uniaxial anisotropy is strongly affected by both Pr and Bi. The anisotropy contributions ΔKu /x<0 and ΔKu/y>0 turn out to be approximately additive. Both Pr and Bi give rise to a pronounced enhancement of the magneto-optical effects. At λ=633 nm θF increases linearly with x and y yielding at T=295 K the contributions ΔθF/x =−3.8×105 deg m−1 and ΔθF/y=−20.6×105 deg m−1, respectively. The bismuth contribution compares well with that observed for various other Bi-substituted rare earth iron garnets.

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