Ni spin coupling and NixN (x = 1, 4) (111) growth at low and room temperatures and different strains using the CrN (111) surface as initial substrate

Abstract

We have investigated the Ni magnetic alignment when deposited on the CrN (111) magnetic surface and the possible growth of NiN and Ni₄N on this surface using first principles calculations. The results revealed that when Ni substituted the Cr atoms of the outermost layer, a switching in the magnetic arrangement, from ferromagnetic to antiferromagnetic, takes place. We have used the surface formation energy (SFE) formalism to establish the thermodynamic stability to study the growth of these nickel nitrides. According to the results, NiN growth yields the formation of only 2 bilayers under N-rich conditions; in contrast, Ni₄N may grow on the CrN (111) substrate. To confirm the stability, ab initio molecular dynamics (AIDM) calculations were performed at 80 K and 300 K; moreover, different strains have been considered in the studies. Our results suggest that the Ni₄N (111) surface may form with a strain substrate up to 6% at low temperatures and below; the compound is stable at room temperature. Beyond this strain, the structure showed a non-crystalline array. In addition, the SFE demonstrated that the N-terminated surface is the most stable configuration under Ni-rich conditions, for example, at 20% N₂ flux. These facts agree well with the experimental data. The magnetic anisotropic energy (MAE) of the NiN structure showed that the Ni spins are pinned to the easy magnetization axis of the CrN (111) surface, and its electronic properties exhibit a metallic character.