Magnetic cluster expansion simulations of FeCr alloys

We present a new method for simulating magnetic alloys characterized by configurational disorder, the magnetic cluster expansion. Each atom in an alloy is assigned a discrete variable denoting the atomic species, and the (continuous) magnetic moment. The parameters of the model are determined by matching energies and magnetic moments of atoms found in trial simulations to DFT calculations. Monte Carlo simulations are then performed to investigate magnetic properties of pure iron, and magnetic and structural properties of FeCr alloys. We found that the Curie temperature of the ordered FeCr alloy with small concentration of Cr (Fe15Cr) increases in comparison with pure Fe and the random mixture of Cr in iron (Fe-6.25% Cr). The method is also applied to the investigation of the correlation functions for the directions of magnetic moments at elevated temperatures.