Two-dimensional binary transition metal nitride $M$N$_4$ ($M$ = V, Cr, Mn, Fe, Co) with a graphene-like structure and strong magnetic properties

Abstract

Binary transition metal nitride with a graphene-like structure and strong magnetic properties is rare. Based on the first-principles calculations, we design two kinds of M N4 (M =transition metal) monolayers, which are transition metal nitrides with a planar structure, made up of M N4 units aligned in the rhombic and squared patterns. The two structural lattices have robust stability and good compatibility with different metal atoms, and the underlying mechanism is the combination of sp 2 hybridization, coordinate bond, and π conjugation. With metal atom changing from V, Cr, Mn, Fe to Co, the total charge of M N4 system increases by one electron in turn, which results in continuous adjustability of the electronic and magnetic properties. The planar ligand field is another feature of the two M N4 lattices, which brings about the special splitting of five suborbitals of 3d metal atom and gives rise to large local moment and strong magnetism. Moreover, we uncover s-CoN4 monolayer to be high temperature ferromagnetic two-dimensional material and the Curie temperatures of 613.9 K is determined by the tensor renormalization group method.