  We theoretically show that the three-dimensional (3D) topological insulator
(TI)/thin-film ferromagnetic metal (FMM) bilayer structure is possible to be a
quantum anomalous Hall (QAH) insulator with a wide global band gap. Studying
the band structure and the weight distributions of eigenstates, we demonstrate
that the attachment of a metallic thin-film on the 3DTI can shift the
topologically non-trivial state into the metal layers due to the hybridization
of bands around the original Dirac point. By introducing the magnetic exchange
interaction in the thin-film layers, we compute the anomalous Hall conductivity
and magnetic anisotropy of the bilayer structure to suggest the appearance of
wider gap realizing QAH effect than usual materials, such as magnetically doped
thin-films of 3DTI and 3DTI/ferromagnetic insulator heterostructures. Our
results indicate that the 3DTI/thin-film FMM bilayer structure may implement
the QAH effect even at room temperature, which will pave a way to the
experimental realization of other exotic topological quantum phenomena.
