Half-metallicity and Ferromagnetism in Penta-AlN2 Nanostructure

We have performed a detailed first-principles study of the penta-AlN2 nanostructure in the Cairo pentagonal tiling geometry, which is dynamically stable due to the absence of imaginary mode in the calculated phonon spectrum. The formation energy and the fragment cohesive energy analyses, the molecular dynamics simulations, and the mechanical property studies also support the structural stability. It could withstand the temperature as high as 1400 K and sustain the strain up to 16.1% against structural collapse. The slightly buckled penta-AlN2 is found to be a ferromagnetic semiconductor. The strain of ~9% could drive the structural transition from the buckled to the planar. Interestingly, the strain of >7% would change the conducting properties to show half-metallic characters. Furthermore, it could be also used to continuously enhance the magnetic coupling strength, rendering penta-AlN2 as a robust ferromagnetic material. These studies shed light on the possibilities in synthesizing penta-AlN2 and present many unique properties, which are worth of further studying on both theory and experiment.