Two-Dimensional Magnetic Semiconductors Based on Transition-Metal Dichalcogenides V $X_2$ ($X$ = S, Se, Te) and Similar Layered Compounds VI$_{{2}}$ and Co(OH)$_{{2}}$

We present a new type of two-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides MX
₂
(M = V, Co; X = S, Se, Te, I, OH) via first-principles calculations. The obtained band gaps of monolayer (ML) VS
₂
, VSe
₂
, and VTe
₂
in the H-phase given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0 μB, while ML VI
₂
and Co(OH)
₂
in the T-phase exhibit energy gaps of 0.96 and 0.08 eV, respectively, with integer magnetic moments of 3.0 μ
_B
. The GGA plus on-site Coulomb interaction U (GGA + U) scheme, which takes the electron-electron correlations in 3d orbitals into account, enhances the exchange splittings, and raises the energy gap of these MLs up to 0.4 to 3 eV. They agree very well with our calculated gaps based on the hybridized functional Heyd-Scuseria-Ernzerhof (HSE) of 0.6 to 3 eV. The wide range of energy gaps provides flexible applications in spintronics. All the calculations demonstrate 100% spin polarized bands around the Fermi level for these MLs. Combining the semiconducting energy gap and the fully spin polarized valence and conduction bands in a single-layer MX
₂
, this new type 2D magnetic semiconductor shows great potential in future spintronics applications.