Ab-initio based models for temperature-dependent magneto-chemical interplay in bccFe-Mn alloys

International audienceBody-centered cubic (bcc) Fe-Mn systems are known to exhibit a complex and atypical magneticbehaviour from both experiments and 0 K electronic-structure calculations, which is due to thehalf-filled 3d-band of Mn. We propose effective interaction models for these alloys, which containboth atomic spin and chemical variables. They were parameterized on a set of key density functionaltheory (DFT) data, with the inclusion of non-collinear magnetic configurations being indispensable.Two distinct approaches, namely a knowledge-driven and a machine-learning approach have beenemployed for the fitting. Employing these models in atomic Monte Carlo simulations enables theprediction of magnetic and thermodynamic properties of the Fe-Mn alloys, and their coupling, asfunctions of temperature. This includes the decrease of Curie temperature with increasing Mnconcentration, the temperature evolution of the mixing enthalpy and its correlation with the alloymagnetization. Also, going beyond the defect-free systems, we determined the binding free energybetween a vacancy and a Mn atom, which is a key parameter controlling the atomic transport inFe-Mn alloys