Ultra-low Young’s modulus and high super-exchange interactions in monolayer CrN: A promising candidate for flexible spintronic applications* *Project supported by the National Natural Science Foundation of China (Grant No. 61888102), the National Key Research and Development Program of China (Grant No. 2016YFA0202300), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB30000000).

Abstract

Monolayer CrN has been predicted to be half-metallic ferromagnet with high Curie temperature. Due to bulk CrN’s biocompatibility, the monolayer is a promising candidate for bio-related devices. Here, using first-principles calculations based on density functional theory, we find that the formation energy of the bulk CrN stacking from layers with square lattice is only 68 meV/atom above the convex hull, suggesting a great potential to fabricate the monolayer CrN in a square lattice by using molecular beam epitaxy method. The monolayer CrN is then proved to be a soft material with an ultra-low Young’s modulus and can sustain very large strains. Moreover, the analysis of the projected density of states demonstrates that the ferromagnetic half-metallicity originates from the splitting of Cr-d orbitals in the CrN square crystal field, the bonding interaction between Cr–N, and that between Cr–Cr atoms. It is worth noting that the super-exchange interaction is much larger than the direct-exchange interaction and contributes to the ultra-high Curie temperature, which is obtained from Monte Carlo simulations based on Heisenberg model. Our findings suggest that the monolayer CrN can be an indispensable candidate for nanoscale flexible spintronic applications with good biocompatibility and is considerable appealing to be realized in experiment.