Alloying vanadium in MnBi2Te4 for robust ferromagnetic coupling and quantum anomalous Hall effect

The intrinsic antiferromagnetic (AFM) interlayer coupling in the two-dimensional magnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}₂{\mathrm{Te}}₄$ places a restriction on realizing a 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 $\mathrm{Mn}{\mathrm{Bi}}₂{\mathrm{Te}}₄$ films by alloying about 50% V with Mn. As a result, the QAHE can be achieved without alternation with the even or odd septuple layers. This provides a practical strategy to get a robust QAHE in ultrathin $\mathrm{Mn}{\mathrm{Bi}}₂{\mathrm{Te}}₄$ films, rendering them attractive for technological innovations.