Evidence of Spin Frustration in Vanadium Diselenide Monolayer Magnet

TL;DR

This study provides spectroscopic evidence that monolayer VSe2 exhibits spin frustration and lacks long-range magnetic order, highlighting complex magnetic interactions in 2D van der Waals materials.

Contribution

It is the first to directly identify spin frustration in monolayer VSe2 using advanced spectroscopic techniques, revealing subtle magnetic correlations without long-range order.

Findings

Monolayer VSe2 is a metallic 1T-phase with vanadium 3d1 configuration.

It exhibits spin frustration with no long-range magnetic order down to 2 K.

Structural features like disorder and edges influence magnetic ground states.

Abstract

Monolayer VSe2, featuring both charge density wave and magnetism phenomena, represents a unique van der Waals magnet in the family of metallic two-dimensional transition-metal dichalcogenides (2D-TMDs). Herein, by means of in-situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, direct spectroscopic signatures are established, that identify the metallic 1T-phase and vanadium 3d1 electronic configuration in monolayer VSe2 grown on graphite by molecular-beam epitaxy. Element-specific X-ray magnetic circular dichroism, complemented with magnetic susceptibility measurements, further reveals monolayer VSe2 as a frustrated magnet, with its spins exhibiting subtle correlations, albeit in the absence of a long-range magnetic order down to 2 K and up to a 7 T magnetic field. This observation is attributed to the relative stability of the ferromagnetic and antiferromagnetic ground states, arising from its atomic-scale structural features, such as rotational disorders and edges. The results of this study extend the current understanding of metallic 2D-TMDs in the search for exotic low-dimensional quantum phenomena, and stimulate further theoretical and experimental studies on van der Waals monolayer magnets.