Title: 2D Materials: Magnetic, Structural, and Electronic properties of MBE grown monolayers of TMDs

Speaker: Dr. Sadhu Kolekar, University of South Florida

Abstract: Monolayer van der Waals materials with ferromagnetic ordering would enable the design of novel van der Waals heterostructures and enable combination of materials that interact via proximity effects but have only weak chemical interactions. Such heterostructures may be fabricated either by mechanical exfoliation and stacking or by direct growth methods. Recently, it has been shown that van der Waals materials with ferromagnetic ordering in the bulk can be reduced to a single layer and still exhibit ferromagnetic ordering.i,ii Also, it has been shown possible that the magnetic properties of such ultrathin materials can be tuned by external electric fieldsiii and exhibit magnetoresistance in magnetic van der Waals heterostructures.iv In general, these materials exhibit however Curie temperatures far below room temperature and thus are not suitable for most applications. Consequently, there has been some interest in van der Waals materials that may exhibit ferromagnetic ordering above room temperature. Density functional theory (DFT) by various groups have predicted ferromagnetic ordering in the family of simple vanadium dichalcogenides, i.e. VX2 with X=S, Se, or Te, with predications of very high Curie temperatures.v,viThese predictions are remarkable, because bulk materials of VX2 are known to be paramagnetic.vii Interestingly, experimental evidence for magnetism in VSe2 mono/few layer materials was found by liquid exfoliationviii. Moreover, monolayers of VSe2 grown by MBE on graphite (HOPG) or MoS2 van der Waals substrateshave been shown by the authors of this article to exhibit ferromagnetism to above room temperature.ix Similar magnetic properties were also recently reported by Duvjir et al. for MBE grown VSe2 on graphene.xThus these measurements indicate ferromagnetic properties in VSe2 for various substrates and even in solution and thus apparently supporting DFT predictions.