Ab initio studies of phase transformations in Fe$_{100-x}$Si$_{x}$

A concentration phase diagram for Fe$_{100-x}$Si$_{x}$ (9.375 $\le x \le$ 25.0 at %) alloys has been built on the base of the structural and magnetic phase transition temperatures estimated theoretically from the first principles. The structural phase transition temperatures for the experimentally observed crystal structures are obtained from the geometric optimization of the crystal structure. The Curie temperatures are estimated in a molecular field approximation using the constants of magnetic exchange interaction calculated ab initio. As temperature increases, the structural transitions from the ordered cubic phase to a completely disordered structure occur via a partially disordered structure over the entire concentration range. As for the magnetic transformations, the ferromagnet–paramagnet transition is observed for all the compositions, but in various crystal phases.