  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.
