Abstract
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\char21{}Ni alloys containing $\ensuremath{\sim}15%\phantom{\rule{0.3em}{0ex}}\mathrm{Ni}$ in an antiferromagnetic (AFM) configuration. These phases of Fe\char21{}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 $^{57}\mathrm{Fe}$ 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\char21{}Ni layers. For the Fe-rich disordered Fe\char21{}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.
Published Version
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