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Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches our understanding of two-dimensional (2D) magnetic orders and presents several advantages over ferromagnetism in spintronic applications. However, studies of 2D intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. Here, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular-beam epitaxy. We observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is ferromagnetic, and correlate its imaged zigzag spin texture with the atomic lattice structure. The AFM order exhibits an intriguing noncollinear spin reorientation under magnetic fields, consistent with its calculated moderate magnetic anisotropy. The findings of this study demonstrate the intricacy of 2D vdW magnetic materials and pave the way for their in-depth analysis. In two dimensions magnetic order without magnetic anisotropy is forbidden, making 2D magnetic systems a rich playground for interesting physics. Here, Xian et al. fabricate monolayers of CrTe2, and demonstrate antiferromagnetic ordering, with spin reorientation at finite magnetic fields. [ABSTRACT FROM AUTHOR]

Manipulating single electrons at the atomic scale is vital for mastering complex surface processes governed by the transfer of individual electrons. Polarons, composed of electrons stabilized by electron-phonon coupling, offer a pivotal medium for such manipulation. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) and density functional theory (DFT) calculations, we report the identification and manipulation of a new type of polaron, dubbed van der Waals (vdW) polaron, within mono- to trilayer ultrathin films composed of Sb 2 O 3 molecules that are bonded via vdW attractions. The Sb 2 O 3 films were grown on a graphene-covered SiC(0001) substrate via molecular beam epitaxy. Unlike prior molecular polarons, STM imaging observed polarons at the interstitial sites of the molecular film, presenting unique electronic states and localized band bending. DFT calculations revealed the lowest conduction band as an intermolecular bonding state, capable of ensnaring an extra electron through locally diminished intermolecular distances, thereby forming an intermolecular vdW polaron. We also demonstrated the ability to generate, move, and erase such vdW polarons using an STM tip. Our work uncovers a new type of polaron stabilized by coupling with intermolecular vibrations where vdW interactions dominate, paving the way for designing atomic-scale electron transfer processes and enabling precise tailoring of electron-related properties and functionalities.

The fabrication of planar heterojunctions with magnetic van der Waals ultrathin crystals is essential for constructing miniaturized spintronic devices but is yet to be realized. Here, we report the growth of CrTe 3 and CrTe 2 ultrathin films with molecular beam epitaxy and characterize their morphological and electronic structure through low-temperature scanning tunneling microscopy/spectroscopy. The former is identified as a Mott insulator, and the latter has shown a robust magnetic order previously. Through vacuum annealing, CrTe 3 can be transformed into CrTe 2 , whose relative ratio is controlled via the annealing time. This renders the feasibility of constructing CrTe 3 -CrTe 2 planar heterojunctions, which express atomically sharp interfaces and smooth band bending. We also identified a superstructure conceivably formed via hybrid units of CrTe 3 and CrTe 2 , whose electronic structure exhibits stunning tunability with the length of the superstructure. Our study sets a foundation for the development of magnetic tunneling junctions for building spintronic circuits and engineering electronic states in artificial superlattice structures.