Effect of magnetic state on the γ-α transition in iron: First-principles calculations of the Bain transformation path

Energetics of the fcc (gamma)-bcc (alpha) lattice transformation by the Bain tetragonal deformation is calculated for both magnetically ordered and paramagnetic (disordered local moment) states of iron. The first-principles computational results manifest a relevance of the magnetic order in a scenario of the gamma-alpha transition and reveal a special role of the Curie temperature of alpha-Fe, T(C), where a character of the transformation is changed. At a cooling down to the temperatures T < T(C) one can expect that the transformation is developed as a lattice instability whereas for T>T(C) it follows a standard mechanism of creation and growth of an embryo of the new phase. It explains a closeness of T(C) to the temperature of start of the martensitic transformation, M(s).