Unique magnetic structure of the vdW antiferromagnet VBr$_3$

TL;DR

This study uncovers the unique antiferromagnetic structure of VBr3 using neutron diffraction, revealing a complex magnetic unit cell with layered antiferromagnetic coupling, contributing new insights into van der Waals magnetic materials.

Contribution

The paper experimentally determines the magnetic structure of VBr3, identifying a novel antiferromagnetic arrangement with a specific propagation vector and space group, not previously characterized.

Findings

Magnetic structure propagation vector k = (1, 0, 0.5)

Magnetic unit cell built from two triple layers with antiferromagnetic coupling

Best fit magnetic space group P-1.1'_c

Abstract

VBr$_3$ is a van der Waals antiferromagnet below the N\'eel temperature of 26.5 K with a saturation moment of 1.2 mB/f.u. above the metamagnetic transitions detected in the in-plane and out-of-plane directions. To reveal the AFM structure of VBr$_3$ experimentally, we performed a single-crystal neutron diffraction study on a large high-quality crystal. The collected data confirmed a slight monoclinic distortion of the high-temperature rhombohedral structure below 90 K. The magnetic structure was, nevertheless, investigated within the R-3 model. The antiferromagnetic structure propagation vector k = (1, 0, 0.5) was revealed. In an attempt to determine the magnetic structure, 72 non-equivalent magnetic reflections were recorded. The experimental data were confronted with the magnetic space groups dictated by the R-3 lattice symmetry and propagation vector. The best agreement between the experimental data and the magnetic structure model was obtained for the space group P-1.1'_c. The magnetic unit cell of the proposed unique antiferromagnetic structure with periodicity 6c is built from two identical triple layers antiferromagnetically coupled along the c axis. Each triple layer comprises a N\'eel antiferromagnetic monolayer sandwiched between two antiferromagnetically coupled ferromagnetic monolayers.