  Based on ab initio calculations, we predict that a monolayer of Cr-doped
(Bi,Sb)2Te3 and GdI2 heterostructure is a quantum anomalous Hall insulator with
a non-trivial band gap up to 38 meV. The principle behind our prediction is
that the band inversion between two topologically trivial ferromagnetic
insulators can result in a non-zero Chern number, which offers a better way to
realize the quantum anomalous Hall state without random magnetic doping. In
addition, a simple effective model is presented to describe the basic mechanism
of spin polarized band inversion in this system. Moreover, we predict that 3D
quantum anomalous Hall insulator could be realized in (Bi2/3Cr1/3)2Te3/GdI2
superlattice.
