VI 3 : A two-dimensional Ising ferromagnet

TLDR: In this paper, the van der Waals (vdW) material was proposed to be a 2D Ising ferromagnet (FM) using density functional calculations, crystal field level diagrams, superexchange model analyses and Monte Carlo simulations.

Abstract: Two-dimensional (2D) magnetic materials are of great current interest for their promising applications in spintronics. Here we propose the van der Waals (vdW) material ${\mathrm{VI}}_{3}$ to be a 2D Ising ferromagnet (FM), using density functional calculations, crystal field level diagrams, superexchange model analyses, and Monte Carlo simulations. The ${a}_{1g}^{1}{e}^{\ensuremath{'}}_{\ensuremath{-}}^{1}$ ground state in the trigonal crystal field gives rise to the 2D Ising FM due to a significant single ion anisotropy (SIA) and enhanced FM superexchange both associated with the ${S}_{z}=1$ and ${L}_{z}=\ensuremath{-}1$ states of ${\mathrm{V}}^{3+}$ ions. We find that a tensile strain on the ${\mathrm{VI}}_{3}$ monolayer further stabilizes the ${a}_{1g}^{1}{e}^{\ensuremath{'}}_{\ensuremath{-}}^{1}$ ground state, and its Curie temperature $({T}_{\mathrm{C}})$ would increase from 70 to 90--110 K under a 2.5%--5% tensile strain. Moreover, we suggest a group of spin-orbital states with a strong SIA which may help to search more 2D Ising magnets.