Sensitive strain effect on magnetic phase transitions in Sb-doped MnBi4Te7 magnetic topological insulator

Recent experiments have successfully fabricated ferromagnetic topological insulator MnBi4Te7 by Sb doping. However, distinct conclusions regarding magnetic phase transitions at different doping concentrations have emerged, alongside controversial interpretations of ferromagnetic origin. Based on first-principles calculations, we demonstrate that the evolution of magnetism in Sb-doped MnBi4Te7 is not only attributed to Mn–Bi/Sb antisite defects, as observed in some experiments, but is also significantly influenced by strain effects. Furthermore, our results reveal that magnetic phase transition is accompanied by a change from n-type to p-type charge carriers at Sb doping concentrations exceeding 30%, in excellent agreement with experimental observation. Moreover, Sb substitution leads to an obvious difference in the effective mass of charge carriers, which qualitatively coincides with experimentally measured carrier mobility. Additionally, Sb doping results in more delocalized charge carriers due to the relatively weaker Sb–Te bonding. Based on these findings, we further discuss how the enhanced carrier delocalization influences interlayer magnetic coupling, leading to a nonmonotonic evolution of long-range magnetism from antiferromagnetic to ferromagnetic and back to antiferromagnetic phases with increased Sb concentration.