Evidence of Spin Frustration in a Vanadium Diselenide Monolayer Magnet

Abstract

Monolayer VSe 2 , 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 3d 1 electronic configuration in monolayer VSe 2 grown on graphite by molecular-beam epitaxy. Element-specific X-ray magnetic circular dichroism, complemented with magnetic susceptibility measurements, further reveals monolayer VSe 2 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. Endowed by the many possible combinations of their constituting elements, two-dimensional transition-metal dichalcogenides (2D-TMDs) can exhibit a multitude of exotic properties. [1, 2] For the much-studied group-VI 2D semiconductors, these include coupled spin and valley Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…A, Crystal structure of 1 T ‐VSe 2 on that of graphite . B, Atomic resolution STM image of monolayer VSe 2 .…”

“…A, Crystal structure of 1 T ‐VSe 2 on that of graphite . B, Atomic resolution STM image of monolayer VSe 2 . C, ARPES intensity map of monolayer VSe 2 in comparison with theoretical spin‐resolved and nonmagnetic electronic bands .…”

“…D, In‐plane magnetic hysteresis of monolayer VSe 2 grown on MoS 2 substrate . E, Magnetic‐field‐dependent out‐of‐plane moment and temperature‐dependent magnetic susceptibility and its inverse of monolayer VSe 2 on graphite . F, Proposed model of 2D triangular spin lattice of monolayer VSe 2 .…”

“…More recently, this issues have been revisited in reference . Combining in situ microscopic and spectroscopic techniques, including STM/STS, synchrotron‐based photoelectron spectroscopy, and ARPES and X‐ray absorption (XAS), the authors have elucidated the metallic 1 T ‐phase (Figure A) and 3 d 1 electronic configuration of MBE‐grown monolayer VSe 2 on graphite.…”

“…Similar results have been demonstrated in monolayer VTe 2 grown on graphite by MBE as well, namely, the metallic 1T-phase, 3d 1 electronic configuration, and no signature of ferromagnetic order intrinsic F I G U R E 5 A, Crystal structure of 1T-VSe 2 on that of graphite. 97 B, Atomic resolution STM image of monolayer VSe 2 . 97 C, ARPES intensity map of monolayer VSe 2 in comparison with theoretical spin-resolved and nonmagnetic electronic bands.…”