Structural $\gamma$-$\varepsilon$ phase transition in Fe-Mn alloys: a CPA+DMFT study

We study the $\gamma$-$\varepsilon$ structural transition in paramagnetic Fe-Mn alloys for Mn content from 10 to 20 at.\% using CPA+DMFT method. This method employs the coherent potential approximation (CPA) combined with the dynamical mean-field theory (DMFT). The material-specific Hamiltonians in the Wannier function basis are obtained by density functional theory. The electronic correlations are found to play a crucial role in this transition. The calculated transition temperature decreases with increasing Mn content and is in a good agreement with experiment. We demonstrate that in contrast to the $\alpha$-$\gamma$ transition in pure iron, the $\gamma$-$\varepsilon$ transition in Fe-Mn alloys is driven by a combination of kinetic and Coulomb energies. The latter is found to be responsible for the decrease of the $\gamma$-$\varepsilon$ transition temperature with Mn content.