Self-Consistent Mapping of the Ab Initio Calculations to the Multi-Orbital p-d Model: Magnetism in alpha-FeSi2 Films as the Effect of the Local Environment

To accurately translate the results obtained within density functional theory (DFT) to the language of many-body theory we suggest and test the following approach: the parameters of the formulated model are to be found from the requirement that the model self-consistent electron density and density of electron states are as close as possible to the ones found from the DFT-based calculations. The investigation of the phase diagram of the model allows us to find the critical regions in magnetic properties. Then the behavior of the real system in these regions is checked by the ab initio calculations. As an example, we studied the physics of magnetic moment (MM) formation due to substitutions of Si by Fe-atoms or vice versa in the otherwise non-magnetic alloy α-FeSi₂. We find that the MM formation is essentially controlled by the interaction of Fe atoms with its next nearest atoms (NNN) and by their particular arrangement. The latter may result in different magnetic states at the same concentrations of constituents. Moreover, one of arrangements produces the counterintuitive result: a ferromagnetism arises due to an increase in Si concentration in Fe_1−xSi_2+x ordered alloy. The existing phenomenological models associate the destruction of magnetic moment only with the number of Fe–Si nearest neighbors. The presented results show that the crucial role in MM formation is played by the particular local NNN environment of the metal atom in the transition metal-metalloid alloy.