Abstract
We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 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. The GGA plus on-site Coulomb interaction U (GGA + U) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics.
Highlights
Two-dimensional materials such as graphene, boron nitride, and transition metal dichalcogenides (TMDs)[20,21,22] with the single-layer thickness less than 1 nm have attracted tremendous attention in recent years
We systematically investigate the electronic structures of monolayer and multilayer VX2 (X = S, Se and Te) in the 2H-phase based on the generalized gradient approximation (GGA) within the density function theory (DFT)
We demonstrate that H-VX2 monolayers exhibit indirect semiconducting energy gaps with intrinsic ferromagnetism and in-plane magnetic anisotropy, achieving an exceptional 2-D magnetic semiconductor group
Summary
The electronic structure calculations of bulk and monolayer VX2 are performed using the projector augmented wave (PAW) method with the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA)[35] as implemented in the VASP package[36,37]. For few layered 2H-VX2 calculations, the van der Waals corrections (vdW-DF)[38] are adopted to optimized the lattice structural parameters and bondlengths. Similar to refs 44 and 45, the convergences of G0W0 energy gaps of VX2 monolayers upon the k-point mesh and the vacuum thickness have been carefully examined with the k-point mesh ranging from 12 × 12 × 1 to 30 × 30 × 1 and the vacuum thickness ranging from 15 Å up to 70 Å and extrapolated to the infinite vacuum thickness limit. To go beyond the standard GGA approach, calculations based on the HSE46 functional have been performed for comparison with the converged G0W0 energy gaps
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