Theoretical study of the environmental effects on the hyperfine fields of Ni and Fe in Ni0.75Fe0.25

The dependence of the hyperfine fields B_hf of Ni and Fe in Ni_0.75Fe_0.25 on the surrounding atomic configuration has been studied by performing charge selfconsistent 6 shell-cluster Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) bandstructure calculations. By replacing the CPA- scatterers in the various shells around the central atom by Ni - or Fe-atoms, respectively, it could be shown that the hyperfine fields vary linearly with the number of Fe-atoms within a given shell and that the changes of B_hf due to simultaneous changes of the atomic configurations of different shells are additive. The changes of the hyperfine fields upon ordering of Ni_0.75Fe_0.25 solid solution as deduced from our calculations agrees reasonably well with experiments.