Structural, electronic, and magnetic properties of vanadium atom-adsorbed MoSe2 monolayer

Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearest-neighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe2, and the peak of density of states right below the Fermi energy is associated with the V-dz(2) orbital. A single V adatom induces a magnetic moment of 5 mu(B) that mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition, the crystal field squashes a part of the V-4 selectrons into the V-3d orbitals, which enhances the local magnetic moment. The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations (GGA) and GGA + U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic (FM) and antiferromagnetic (AFM) states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA+ U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.