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Effect of local environment on moment formation in iron silicides

The effect of local environment on the formation of magnetic moments on Fe atoms in iron silicides are studied by combination of ab initio and model calculations. The suggested model includes all Fe d- and Si p-orbitals, intra-atomic Coulomb interactions, inter-atomic Fe-Fe exchange and hopping of electrons to nearest and next nearest neighboring atoms and takes into account all symmetries within the Slater-Koster scheme. The parameters of the model are found from the requirement that self-consistent moments on atoms and density of states found from ab initio and model calculations within the Hartree-Fock approximation are close to each other as much as possible. Contrary to the commonly accepted statement that an increase of the Si concentration within nearest environment of Fe atoms in the ordered Fe3Si and FexSi1-x alloys leads to a decrease of Fe magnetic moment we find that a crucial role in the formation of magnetic moments is played by second coordination sphere of Fe atoms. Particularly, the Fe atoms have higher magnetic moments in amorphous films compared to the epitaxial ones due to decrease in the number of iron-atoms in the next nearest environment. Both our model and ab initio calculations confirm existence of known spin crossover with pressure and predict second crossover at higher pressure