Stability and Antisite Defect formation in MnBi₂Te₂Se₂

We explore the stability of MnBi₂Te₂Se₂ (MBTS) through Density Functional Theory (DFT) and quantum Monte Carlo (QMC) calculations. As an intrinsic magnetic topological material, the parent compound MnBi₂Te₄ (MBT) has garnered significant interest, with ongoing efforts to optimize its properties. Similarly, layered MnBi₂Se₄ (MBS), recently synthesized via non-equilibrium molecular beam epitaxy, has been experimentally established as a topological insulator [1]. Our analysis of MBTS encompasses formation enthalpies, free energies, defect formation energies, and dynamical stability. According to our QMC calculations, MBTS is thermodynamically stable and exhibits a higher Mn-Bi antisite pair formation energy than MBT. Extensive defect formation energy calculations using DFT indicate MBTS's resistance to various defect formations. Additionally, we examine MnBi₂Te₄₋ₓSe₄₊ₓ, with x ranging from 0 to 4, through cluster expansion models to investigate Se/Te ordering in this material system.

[1] Nano Letters, 2021, 21, 5083-5090