Robust ferromagnetism in single-atom-thick ternary chromium carbonitride CrN4C2

The design and exploration of ferromagnetic two-dimensional materials is an important research topic due to their potential applications in spintronic devices. By the first-principles calculations, we examine the structural stability and the electronic properties of transition metal carbonitrides MN4C2 (M = 3d transition metals) and find out that chromium carbonitride CrN4C2 is a ferromagnetic two-dimensional material. CrN4C2 is made up of CrN4 unit and C2 dimer, stacked alternatively to form a planar single-atom-thick sheet. For the Cr 3d electronic states, there is a complete spin splitting between Cr 3d spin-up and spin-down states, leading to a large moment up to 3.76 μB around Cr atoms. The magnetic interaction among Cr atoms can be described by Ising model, and the ferromagnetic couplings are energetically favorable, which indicates that there must be a ferromagnetic phase transition and a ferromagnetic ground state. The Curie temperature of CrN4C2 is evaluated to be 226.6 K in terms of the tensor renormalization group method. With Hubbard U of 3 eV and 5 eV being considered, the Curie temperatures reach up to 331.1 and 283.6 K. Consequently, our results demonstrate that CrN4C2 is a graphene-like two-dimensional material with robust ferromagnetism.