Calculations of Bulk-Like Transition Temperatures of Rare Earth-Transition Metal Alloys AcB1-c Using the Effective Field Theory

Abstract

The mean bulk-like transition temperatures are calculated as a function of the concentration c in the simple cubic Ising ferrimagnetic alloys A c B 1--c which have an antiferromagnetic coupling between the A and B species. The application of the calculations to the alloy Fe c Gd 1--c is presented. An effective field theory that goes beyond the mean-field approximation is used, yielding spin values and effective exchange interaction energies. A calculation is presented for the phase diagram, giving the Curie and the compensation temperatures as a function of the alloy concentration c for given magnetic exchange constants. Such a diagram is described as a function of the J Gd-Fe , J Gd-Gd , and J Fe-Fe exchange integral values. A fixed set of exchange interactions in the entire concentration range 0 c 1 is defined. The numerical calculations show that there is an overall qualitative agreement between theory and experiment in this range.