Electronic structure and magnetism of MTe2 (M = Ti, V, Cr, Mn, Fe, Co and Ni) monolayers

We study the electronic structure and magnetism of monolayer 3d transition-metal ditellurides MTe2 (M = Ti, V, Cr, Mn, Fe, Co and Ni) in trigonal prismatic H- and/or octahedral T-phase by means of the first-principles calculations. The results show that H-VTe2, T-VTe2, H-FeTe2 and T-MnTe2 monolayers exhibit intrinsic ferromagnetism, and the others have no ferromagnetism. The exchange splitting of V, Mn and Fe 3d orbitals is responsible for ferromagnetism. The exchange constant and the Curie temperature are estimated by using 2D Ising model and mean field theory. Among the four ferromagnetic monolayers, the H-VTe2 monolayer has the largest exchange constant and the corresponding Curie temperature is near room temperature. Calculations also show that the T-VTe2, H-VTe2 and H-FeTe2 monolayers have in-plane easy magnetization direction, while the easy direction of the T-MnTe2 monolayer is perpendicular to the layer. Moreover, we analyze the relative exchange strength of the four ferromagnetic monolayers based on the competition between the through-bond ferromagnetic interaction and the through-space antiferromagnetic interaction according to the Goodenough–Kanamori rules. The magnetocrystalline anisotropy is explained qualitatively based on the second-order perturbation theory from the spin-orbit coupling between 3d orbitals of M atoms.