Ferroelectricity and ferromagnetism in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>VO</mml:mi><mml:msub><mml:mi mathvariant="normal">I</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> monolayer: Role of the Dzyaloshinskii-Moriya interaction
Ning Ding, Jun Chen, Shuai Dong, Alessandro Stroppa
Abstract
Multiferroics with intrinsic ferromagnetism and ferroelectricity are highly desired but rather rare, while most ferroelectric magnets are antiferromagnetic. A recent theoretical work [Tan et al., Phys. Rev. B 99, 195434 (2019)] predicted that oxyhalides $\mathrm{VO}{X}_{2}$ ($X$: halogen) monolayers are two-dimensional multiferroics by violating the empirical ${d}^{0}$ rule. Most interestingly, the member $\mathrm{VO}{\mathrm{I}}_{2}$ are predicted to exhibit spontaneous ferromagnetism and ferroelectricity. In this work, we extend the previous study on the structure and magnetism of $\mathrm{VO}{\mathrm{I}}_{2}$ monolayer by using density-functional theory and Monte Carlo simulation. The presence of the heavy element iodine with a strong spin-orbit coupling gives rise to an effective Dzyaloshinskii-Moriya interaction in the polar structure, which favors a short-period spiral 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 $\mathrm{VO}{\mathrm{I}}_{2}$ 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.