Ferroelectricity and ferromagnetism in VOI$_2$ monolayer: the role of Dzyaloshinskii-Moriya interaction

TL;DR

This study investigates VOI$_2$ monolayer, revealing that Dzyaloshinskii-Moriya interaction influences its magnetic structure and that Coulomb interactions can switch it between ferroelectric insulator and ferromagnetic metal states.

Contribution

It extends previous work by using density functional theory and Monte Carlo simulations to elucidate the role of Dzyaloshinskii-Moriya interaction in VOI$_2$ monolayer's multiferroic properties.

Findings

Dzyaloshinskii-Moriya interaction favors spiral magnetic structures.

On-site Coulomb interaction suppresses polar distortion.

VOI$_2$ can be a ferroelectric insulator with spiral magnetism or a ferromagnetic metal.

Abstract

Multiferroics with intrinsic ferromagnetism and ferroelectricity are highly desired but rather rare, while most ferroelectric magnets are antiferromagnetic. A recent theoretical work [Phys. Rev. B {\bf 99}, 195434 (2019)] predicted that oxyhalides VO$X_2$ ($X$: halogen) monolayers are two-dimensional multiferroics by violating the empirical $d^0$ rule. Most interestingly, the member VOI$_2$ are predicted to exhibit spontaneous ferromagnetism and ferroelectricity. In this work, we extend the previous study on the structure and magnetism of VOI$_2$ monolayer by using density functional theory and Monte Carlo simulation. The presence of the heavy element iodine with a strong spin-orbit coupling leads an effective Dzyaloshinskii-Moriya interaction in the polar structure, which favors a short-period spiral a magnetic structure.. Another interesting result is that the on-site Coulomb interaction can strongly suppress the polar distortion thus leading to a ferromagnetic metallic state. Therefore, the VOI2 monolayer is either a ferroelectric insulator with spiral magnetism or a ferromagnetic metal, instead of a ferromagnetic ferroelectric system. Our study highlights the key physical role of the Dzyaloshinskii-Moriya interaction.