Modified mean-field model for rare-earth-iron amorphous alloys

A mean-field model of the magnetic properties of amorphous rare-earth-iron alloys has been developed which incorporates an Fe spin whose dependence on both the concentration and the species of rare earth is based on Mössbauer spectra. Using this model with a single fixed set of exchange constants, we have been able to calculate Curie temperatures which are in reasonable agreement with the data for amorphous rare-earth (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu-iron alloys containing between 50 and 100 at.% iron. Better agreement with the measured Curie temperatures is achieved if the magnitudes of the Fe-Fe and rare-earth-Fe exchange constants are allowed to increase linearly with rare-earth concentration. The latter case has the additional advantage of reproducing the observed shape of the magnetization-vs-temperature curves for wide range of composition and rare-earth species.