Direct observation of van der Waals stacking–dependent interlayer magnetism

Abstract

Controlling the crystal structure is a powerful approach for manipulating the fundamental properties of solids. Unique to two-dimensional (2D) van der Waals materials, the control can be achieved by modifying the stacking order through rotation and translation between the layers. Here, we report the first observation of stacking dependent interlayer magnetism in the 2D magnetic semiconductor, chromium tribromide (CrBr 3 ), enabled by the successful growth of its monolayer and bilayer through molecular beam epitaxy. Using in situ spin-polarized scanning tunneling microscopy and spectroscopy, we directly correlated the atomic lattice structure with observed magnetic order. We demonstrated that while individual CrBr 3 monolayer is ferromagnetic, the interlayer coupling in bilayer depends strongly on the stacking order and can be either ferromagnetic or antiferromagnetic. Our observations provide direct experimental evidence for exploring the stacking dependent layered magnetism, and pave the way for manipulating 2D magnetism with unique layer twist angle control.

Low-temperature monoclinic layer stacking in atomically thin CrI3 crystals

“…This picture is in agreement with recent measurements on few-layer CrI 3 where either an accidental puncture 14 or an external pressure 25,26 provided the energy to undergo a structural transformation with a corresponding transition to FM ordering. Additional validations supporting the connection between crystal structure and magnetism have been achieved in a related material, CrBr 3 , by observing different magnetic ordering associated with novel stacking patterns (not corresponding to the bulk phases) in bilayers grown by molecular beam epitaxy 27 . The ultimate confirmation of the proposed scenario requires a technique sensitive to the stacking order of few layer structures in order to verify the absence of structural phase transition in few layers.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…From an experimental perspective, direct observation of stacking-dependent interlayer magnetism in CrBr 3 has been realized successfully. 75 This study shows that while molecular beam epitaxy (MBE)-grown monolayer CrBr 3 is ferromagnetic, the interlayer coupling in its bilayer can be either ferromagnetic or antiferromagnetic depending on the exact stacking order. Figure 3A illustrates the atomic structure of Cr 2 Ge 2 Te 6 (CGT), 76 a 2D Heisenberg ferromagnet with a small out-ofplane magnetocrystalline anisotropy that results from its slightly distorted Cr-Te 6 octahedral cage with spin-orbit coupling on the Cr ions.…”

Prospects and Opportunities of 2D van der Waals Magnetic Systems

“…using in situ spin‐polarized scanning tunneling microscopy. [ 169 ] They found that when two single layer CrBr 3 stacked together has the same orientation, the bilayer CrBr 3 is antiferromagnetic. But when two single‐layer CrBr 3 oriented in the opposite direction(correspond to a 180° rotation between layers) are stacked together, the resulting bilayer CrBr 3 is ferromagnetic.…”

“…But when two single‐layer CrBr 3 oriented in the opposite direction(correspond to a 180° rotation between layers) are stacked together, the resulting bilayer CrBr 3 is ferromagnetic. [ 169 ] Although both the detailed physics of this orientation‐dependent magnetism and the growth mechanism for specific stacking order need to be further investigated, these results demonstrate that vdW heterostructure is a promising way to manipulate magnetic properties of 2D materials.…”