A theoretical study of the hyperfine fields in BCC Fe_xCr_1-x and Fe_xCo_1-x alloys

The hyperfine fields in the substitutionally disordered BCC alloy systems Fe_xCr_1-x and Fe_xCo_1-x have been studied by means of charge self-consistent Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) electronic structure calculations. For the various components, the contribution to the Fermi contact hyperfine field due to core polarisation was found to be proportional to the corresponding local spin moment. The contributions of the conduction band, however, did not show such a simple behaviour and turned out to be dominated by the occupation of the s bands for spin up and down. To study the influence of relativistic effects on the hyperfine fields the corresponding matrix elements for the Fermi contact interaction have been calculated nonrelativistically as well as fully relativistically. The importance of contributions to the hyperfine fields coming from non-s electrons have been investigated by performing spin-polarised relativistic linear muffin tin orbital method (SPRLMTO) band structure calculations for hypothetically ordered alloys.