Prediction of transition metal carbonitride monolayers MN4C6 (M = Cr, Mn, Fe, and Co) made up of a benzene ring and a planar MN4 moiety

Abstract

Based on first-principles calculations, we predict a class of graphene-like magnetic materials, transition metal carbonitrides MN₄C₆ (M = Cr, Mn, Fe, and Co), which are made up of a benzene ring and an MN₄ moiety, two common planar units in the compounds. The structural stability is demonstrated by the phonon and molecular dynamics calculations, and the formation mechanism of the planar geometry of MN₄C₆ is ascribed to the synergistic effect of sp² hybridization, M–N coordination bond, and π–d conjugation. The MN₄C₆ materials consist of only one layer of atoms and the transition metal atom is located in the planar crystal field, which is markedly different from most two-dimensional materials. The calculations indicate that MnN₄C₆, FeN₄C₆, and CoN₄C₆ are ferromagnetic while CrN₄C₆ has an antiferromagnetic ground state. The Curie temperatures are estimated by solving the anisotropic Heisenberg model with the Monte Carlo method.