Alloying V in MnBi${}_2$Te${}_4$ for Robust Ferromagnetic Coupling and Quantum Anomalous Hall Effect

The intrinsic antiferromagnetic (AFM) interlayer coupling in two-dimensional magnetic topological insulator MnBi${}_2$Te${}_4$ places a restriction on realizing stable quantum anomalous Hall effect (QAHE) [Y. Deng et al., Science 367, 895 (2020)]. Through density functional theory calculations, we demonstrate the possibility of tuning the AFM coupling to the ferromagnetic coupling in MnBi${}_2$Te${}_4$ films by alloying about 50% V with Mn. As a result, QAHE can be achieved without alternation with the even or odd septuple layers. This provides a practical strategy to get robust QAHE in ultrathin MnBi${}_2$Te${}_4$ films, rendering them attractive for technological innovations.