Modeling Defects and Phase Stability in MnBi₂Te₄ at Finite Temperatures

MnBi₂Te₄ (MBT) has attracted attention as an intrinsic magnetic topological material with potential in quantum computing, and other practical application due to its quantum Hall effect. However, Mn_Bi and Bi_Mn antisite defects become prominent at elevated temperatures, limiting potential applications. Recent zero-Kelvin DFT and QMC (density functional theory, quantum Monte Carlo, ab-initio) calculations fail to capture the finite-temperature behavior observed experimentally. To address this, we incorporate configurational entropy in characterizing MBT's phase diagram at finite temperatures accounting for defect interactions. Our approach goes beyond the calculation of the configurational entropy from non-interacting isolated defects. We show that MBT undergoes a second-order order/disorder phase transition explaining the abundance of defects in experiments at synthesis temperature (852 K). Above the synthesis temperatures nearly 2/3^rd of Mn sites would be occupied by Bi, indicating highly disordered configuration. We aim to extend this study further including departures of stoichiometry and by refining our model correcting DFT with QMC energies to improve predictions of MBT stability at finite temperatures.