Theoretical study of magnetism and Mössbauer hyperfine interactions in ordered FeNi and disordered fcc Fe-rich Fe–Ni alloys

Electronic structure spin-polarized calculations with the discrete variational method in density functional theory were performed for 79-atoms embedded clusters modeling the ferromagnetic (FM) ordered layered compound FeNi (tetrataenite), as well as disordered Fe-rich fcc Fe--Ni alloys containing ~15%0.3em0exNi in an antiferromagnetic (AFM) configuration. These phases of Fe--Ni may be obtained by synthetic means, and are also present in meteorites. Spin magnetic moments and spin density maps were obtained from the calculations. The ⁵⁷Fe M\"ossbauer hyperfine parameters isomer shift, quadrupole shift and magnetic hyperfine fields were calculated with the self-consistent charge and spin densities obtained. It was found that for FM ordered FeNi the electric-field gradient is positive; this result, together with the measured positive value of the quadrupole shift, proves that the direction of magnetization is perpendicular to the Fe--Ni layers. For the Fe-rich disordered Fe--Ni alloys with AFM configuration, it was found that the lower values of the isomer shift relative to tetrataenite can only be explained by a lattice contraction.