Influence of magnetic excitation and vibrational entropy on the phase diagram of Fe1−xCrx alloys

Abstract

We study the thermodynamic properties of iron-chromium alloys in the framework of the Magnetic Cluster Expansion, a model of effective interactions explicitly taking into account the atomic magnetic moments. Monte Carlo simulations are used to study the magnetic properties and measure the mixing enthalpies of disordered solid solutions. The phase diagram of the Fe-Cr system is established by simulations performed in the canonical and semi-grand canonical ensembles, which require the relaxation of the chemical and magnetic configurations. The effect of magnetism on thermodynamic properties is highlighted via simulations with a fixed spin temperature, in order to impose specific magnetic states. We also propose a simple method to introduce the vibrational entropy in the framework of the Magnetic Cluster Expansion. These simulations allow us to estimate the respective weights of the chemical, magnetic and vibrational contributions and we conclude that they have all a significant effect on the thermodynamics of iron-chromium alloys.