Ferromagnetic 2D Materials

Two-dimensional transition-metal dichalcogenides (2DTMDs) exhibit a multitude of exotic properties. These properties can be exploited as potential building blocks for applications in electronic, magnetic, storage, sensing, or catalytic applications. 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 <i>et al</i>. reported strong room-temperature ferromagnetism in VSe₂ monolayers on van der Waals substrates. We show however, that 2D 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.<br/> <br/>We have addressed the conflicting reports on the ferromagnetism of clean monolayer VSe₂. We studied the controllable formation of 1D defect line patterns in vanadium diselenide (VSe₂) monolayers using scanning tunneling microscopy and q-plus atomic force microscopy 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 density functional theory 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, which influence potential device performance. We also discuss magnetic Cr selenides and tellurides that we have recently worked with, that show evidence of Curie temperatures above room temperature.