Effect of magnetic state on the $\gamma -\alpha$ transition in iron: First-principle calculations of the Bain transformation path

Abstract

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-principle 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, $M_s$.

4 pages, 3 figures, submitted in Phys. Rev. Letters

References in corpus (3)

• Entropy driven stabilization of energetically unstable crystal structures explained from first principles theory
• Magnetism and local distortions near carbon impurity in $\gamma$-iron
• Spin waves in paramagnetic BCC iron: spin dynamics simulations

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