Penta-AlN2 monolayer: A ferromagnetic insulator

A ferromagnetic insulating behavior is necessary to realize quantum anomalous Hall effect. Here we study, using first-principles calculations and a Monte Carlo simulation, the electronic structure and magnetism of AlN2 monolayer. Our results show that the AlN2 monolayer has a ferromagnetic insulating behavior. By using the crystal field analysis, we find that the axes of the neighboring N-2 dimers are perpendicular, and the superexchange between them accounts for the ferromagnetic (FM) order in the AlN2 monolayer. We also carried out a Monte Carlo simulation, which shows that the AlN2 monolayer remains FM with Curie temperature (T-c) similar to 22 K. Moreover, the tensile strain would make a stronger overlap between the neighboring N-2 dimers, and steadily enhances the FM stability. As a result, the T-c can be increased with the tensile strain.