  Two-dimensional (2D) magnetic materials with nontrivial topological states
have drawn considerable attention recently. Among them, 2D metal-organic
frameworks (MOFs) are standing out due to their advantages, such as the easy
synthesis in practice and less sensitivity to oxidation that are distinctly
different from inorganic materials. By means of density-functional theory
calculations, we systematically investigate the electronic and topological
properties of a class of 2D MOFs X(C21H15N3) (X = transition metal element from
3d to 5d). Excitingly, we find that X(C21H15N3) (X = Ti, Zr, Ag, Au) are Chern
insulators with sizable band gaps (~7.1 meV). By studying a four-band effective
model, it is revealed that the Chern insulator phase in X(C21H15N3) (X = Ti,
Zr, Ag, Au) is caused cooperatively by the band inversion of the p orbitals of
the C21H15N3 molecule and the intrinsic ferromagnetism of X(C21H15N3).
Additionally, Mn(C21H15N3) is a Dirac half-metal ferromagnet with a high Curie
temperature up to 156 K. Our work demonstrates that 2D MOFs X(C21H15N3) are
good platforms for realizing Quantum anomalous Hall effect and designing novel
spintronic devices based on half-metals with high-speed and long-distance spin
transport.
