Institute of Quantum Materials Science, IQMS

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

S. V. Okatov, A. R. Kuznetsov and Yu. N. Gornostyrev , V. N. Urtsev, M. I. Katsnelson

Physical Review B 79, 094111(2009)

Energetics of the fcc (γ)-bcc (α) 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 γ-α transition and reveal a special role of the Curie temperature of α-Fe, TC, where a character of the transformation is changed. At a cooling down to the temperatures T< TC one can expect that the transformation is developed as a lattice instability whereas for T> TC it follows a standard mechanism of creation and growth of an embryo of the new phase. It explains a closeness of TC to the temperature of start of the martensitic transformation, Ms.

Variation in the total energy per atom along the Bain deformation path for different magnetic states. FM (empty triangles) and AFM (solid triangles) label collinear ferromagnetic and antiferromagnetic structures, SS (empty circles)— spin-spiral state, DLM (crosses)—disordered local moments, DLM0.5 (empty diamonds)—DLM state with the total magnetic moment equal to half of that for the FM state.