Lattice Distortions and Magnetic Interactions in Single-Layer VOCl

TL;DR

This study reveals that monolayer VOCl exhibits monoclinic lattice distortions and complex magnetic interactions, with higher-order magnetic terms crucial for stabilizing its magnetic ground state, challenging previous assumptions of orthorhombic symmetry.

Contribution

It demonstrates through ab-initio calculations that monolayer VOCl has monoclinic distortions and complex magnetic interactions, highlighting the importance of higher-order magnetic terms.

Findings

Monolayer VOCl exhibits monoclinic lattice symmetry.

Competing magnetic interactions lead to a frustrated magnetic structure.

Higher-order magnetic interactions are essential for stabilizing the magnetic ground state.

Abstract

Atomically thin layers exfoliated from magnetic van der Waals layered materials are currently of high interest in solid state physics. VOCl is a quasi-two-dimensional layered antiferromagnet which was recently synthesized in monolayer form. Previous theoretical studies have assumed the high-temperature orthorhombic lattice symmetry also in the low temperature range, where the bulk system is known to be monoclinic due to a strong magnetoelastic coupling. We demonstrate from \textit{ab-initio} calulations that this monoclinic distortion is prevalent also in monolayers, which is in line with recent experimental indications of monoclinic symmetry. Our calculations also show that competing ferromagnetic and antiferromagnetic interactions give rise a frustrated two-fold magnetic superstructure where higher-order magnetic interactions play a key role to stabilize the observed magnetic ground state.