Prof. Andrew T. S. Wee, Department of Physics, National University of Singapore
Is 2D Vanadium Diselenide Ferromagnetic?
2D transition-metal dichalcogenides (2D TMDs) exhibit a multitude of exotic properties. In particular, if 2D van der Waals magnets exist, they would be ideal atomically thin building blocks for 2D spintronics . Theories have predicted intrinsic magnetism in 2D VX2, such as vanadium diselenide and vanadium ditelluride. Bonilla et al. reported strong room-temperature ferromagnetism in 1T-VSe2 monolayers on van der Waals substrates . We show however, that 2D 1T-VSe2 is not intrinsically ferromagnetic, but displays evidence of spin frustration . Nevertheless, a magnetic transition in 2D VSe2 can be induced at the contamination-free interface between Co and VSe2 via interface hybridization . Promotion of ferromagnetism in 2D VSe2 is accompanied by antiferromagnetic coupling to Co and a reduction in the spin moment of Co. Consistent results are obtained for 2D VTe2 .
We have addressed the conflicting reports on the ferromagnetism of clean monolayer VSe2. We studied the controllable formation of 1D defect line patterns in VSe2 monolayers using STM and q-plus AFM techniques . We found that the reconstructed VSe2 monolayer with Se-deficient line defects displays room-temperature ferromagnetism under X-ray magnetic circular dichroism and magnetic force microscopy, consistent with the DFT calculations. This work possibly resolves the controversy on whether monolayer VSe2 is intrinsically ferromagnetic, and highlights the importance of controlling surface defects in 2D crystals.
 W. Zhang, P. K. J. Wong, R. Zhu, A. T. S. Wee, InfoMat. (2019) 1, 1–17.
 M. Bonilla et al., Nat. Nano. (2018) 13, 289-293.
 P. K. J. Wong et al., Adv. Mater. (2019) 31, 1901185.
 W. Zhang et al., ACS Nano (2019) 13, 8997-9004
 P. K. J. Wong et al., ACS Nano (2019) 13, 11, 12894–12900
 R. Chua et al., Adv. Mater. (2020) 200069