Dative epitaxy of covalent 2D magnets

Moiré superlattices formed by stacking two-dimensional (2D) van der Waals (vdW) materials have become promising platforms for studying emergent phenomena. However, moiré superlattices obtained by exfoliation and restacking via aligning/twisting van der Waals layers are typically small in size and accompanied by gradual spatial modulation or local domain formation.

In this work, we report hybrid covalent-vdW moiré superlattices of Cr₅Te₈/WSe₂ by epitaxial growth of the covalently bonded 2D magnet Cr₅Te₈ on top of a semiconducting vdW monolayer WSe₂ template, via a two-step chemical vapor deposition process. The thickness of Cr₅Te₈ is tunable down to a single unit cell, with a lateral dimension of up to 50 µm. The Cr self-intercalation within the vdW gap creates a Te-Cr-Se Janus interface with covalent-like bonding, which is absent in fully vdW heterostructures. The strong interlayer coupling stabilizes the metastable trigonal structure of Cr₅Te₈ to form a perfectly commensurate 3 × 3/7 × 7 Moiré superlattice via lattice strain. Magnetic domain structures of Cr₅Te₈ imaged by photoemission electron microscopy reveal distinct domain patterns in the 2D limit in which the shape and size are dramatically different from those of thicker samples. Magnetization reversal is further studied by reflective magnetic circular dichroism down to a thickness of two unit cells. Our work expands moiré superlattices into the regime of strong interlayer-coupling.