Magnetization of amorphous RE_x-Cu_1-x alloys (RE=Gd, Tb, Dy, Ho)

Films of amorphous RExCu1-x (RE=Gd, Tb, Dy, Ho: 0.30≤x≤0.60) were prepared by two source evaporation of the elements. Magnetization measurements were made at 4.2 K with a vibrating sample magnetometer in applied fields up to 70 kOe. In the case of the Gd alloys, the magnetization is consistent with a fully aligned moment of 7μB. The dependence of the Curie temperatures on x can be understood in terms of a nearest neighbor statistical model with a percolation limit of x=0.33. In the case of Tb, Dy, Ho alloys, the magnetization is considerably less than that expected for fully aligned moments. The degree to which the magnetization is reduced is proportional to the Stevens factor of the RE confirming that the reduction is due to local anisotropy effects. The field dependence of the magnetization is consistent with existing models but the dependence of H c on D/J does not agree with the theory.