  In this study, based on the first-principles calculations, we systematically
investigated the electronic and magnetic properties of the transition
metal-oxide-incorporated 2D g-C3N4 nanosheet (labeled C3N4-TM-O, TM = Sc-Mn).
The results suggest that the TM-O binds to g-C3N4 nanosheets strongly for all
systems. We found that the 2D C3N4-TM-O framework is ferromagnetic for TM = Sc,
Ti, V, Cr, while it is antiferromagnetic for TM = Mn. All the ferromagnetic
systems exhibit the half-metallic property. Furthermore, Monte Carlo
simulations based on the Heisenberg model suggest that the Curie temperatures
(T_c) of the C3N4-TM-O (TM = Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K,
and 190 K, respectively. Based on Bader charge analysis, we found that the
origin of the half-metallicity at Fermi energy can be partially attributed to
the transfer of electrons from TM atoms to the g-C3N4 nanosheet. In addition,
we found that not only electrons but also holes can induce half-metallicity for
2D g-C3N4 nanosheets, which may help to understand the origin of
half-metallicity for graphitic carbon nitride.
