Effect of Ni deposition on CrI3 monolayer: First-principles study

Abstract

In our recent experimental work, we demonstrated that Ni thin film deposition can be used to tune the surface magnetic states in bulk CrI₃. Here, we present the results of a computational study of Ni deposition on a CrI₃ monolayer. In particular, we compare structural, electronic, and magnetic properties of three different systems: a pristine CrI₃ monolayer, a CrI₃ monolayer with partial Ni coverage, and a CrI₃ monolayer with full Ni coverage. The corresponding cells used in our calculations are Cr₂I₆, Cr₂I₆Ni₁, and Cr₂I₆Ni₃. In Cr₂I₆Ni₁, the Ni atom is positioned over the hollow site, which corresponds to the lowest energy configuration. In Cr₂I₆Ni₃, the three Ni atoms are positioned over the single hollow site, and over the two Cr sites. Our calculations indicate that the partial coverage of CrI₃ monolayer with Ni retains the semiconducting nature of the parent compound, but results in a strong reduction of the energy band gap. At the same time, the full coverage of CrI₃ monolayer with Ni results in a metallic transition, with a highly spin-polarized (possibly half-metallic) electronic structure. The magnetic alignment of the CrI₃ monolayer with the deposited Ni is ferrimagnetic, due to the anti-aligned magnetic moments of Cr and Ni atoms. While the partial coverage of the CrI₃ monolayer with Ni has a moderate impact on the lattice parameter of the parent compound, full coverage by Ni results in a significant increase of the lattice constant. For both partial and full coverages, the lowest energy configuration corresponds to the Ni atoms being approximately aligned with the out-of-plane coordinate of the surface iodine layer. In addition, in the full coverage mode, the Cr layer exhibits a significant shift away from the Ni atoms, effectively “detaching” the Ni / I atomic layer from the rest of the cell.