Magnetic monolayer Li$_{2}$N: Density Functional Theory Calculations

Abstract

Density functional theory (DFT) calculations are used to investigate the electronic and magnetic structures of a two-dimensional (2D) monolayer Li$_{2}$N. It is shown that bulk Li$_{3}$N is a non-magnetic semiconductor. The non-spinpolarized DFT calculations show that $p$ electrons of N in 2D Li$_{2}$N form a narrow band at the Fermi energy $E_{\rm{F}}$ due to a low coordination number, and the density of states at the Fermi energy ($g(E_{\rm{F}}$)) is increased as compared with bulk Li$_{3}$N. The large $g(E_{\rm{F}}$) shows instability towards magnetism in Stoner's mean field model. The spin-polarized calculations reveal that 2D Li$_{2}$N is magnetic without intrinsic or impurity defects. The magnetic moment of 1.0\,$\mu_{\rm{B}}$ in 2D Li$_{2}$N is mainly contributed by the $p_{z}$ electrons of N, and the band structure shows half-metallic behavior. {Dynamic instability in planar Li$_{2}$N monolayer is observed, but a buckled Li$_{2}$N monolayer is found to be dynamically stable.} The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the N atoms is also investigated to access the exchange field strength. {We found that planar (buckled) 2D Li$_{2}$N is a ferromagnetic material with Curie temperature $T_{c}$ of 161 (572) K.}