Self-consistent mapping of the ab initio calculations to the multi-orbital p-d-model: Magnetism in **α**-FeSi_{2} films as effect of local environment

V. Zhandun^{+*}, N. Zamkova^{+}, S. Ovchinnikov^{+}, I. Sandalov^{+}

^{+}Kirensky Institute of Physics, Federal Research Center "Krasnoyarsk Science Centre,

Siberian Branch of the Russian Academy of Sciences", 660036 Krasnoyarsk, Russia

^{*}Reshetnev Siberian State Aerospace University, 660037 Krasnoyarsk, Russia

**Abstract**

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 behaviour 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-FeSi_{2}. 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 counter-intuitive result: a
ferromagnetism arises due to an increase of Si concentration in
Fe_{1-x}Si_{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.