First-principles study of multifunctional Mn2B3 materials with high hardness and ferromagnetism

Abstract

Transition metal boride TM₂B₃ is widely studied in the field of physics and materials science. However, Mn₂B₃ has not been found in Mn–B systems so far. Mn₂B₃ undergoes phase transitions from Cmcm (0–28 GPa) to C2/m (28–80 GPa) and finally to C2/c (80–200 GPa) under pressure. Among these stable phases, Cmcm- and C2/m-Mn₂B₃s comprise six-membered boron rings and C2/c-Mn₂B₃ has wavy boron chains. They all have good mechanical properties and can become potential multifunctional materials. The strong B–B covalent bonding is mainly responsible for the structural stability and hardness. Comparison of the hardness of the five TM₂B₃s with different bonding strengths of TM–B and B–B bonds reveals a nonlinear change in the hardness. According to the Stoner model, these structures possess ferromagnetism, and the corresponding magnetic moments are almost the same as those of GGA and GGA + U (U = 3.9 eV, J = 1 eV).