Van der Waals epitaxial growth of air-stable CrSe nanosheets with thickness-tunable magnetic order.

The discovery of intrinsic ferromagnetism in ultrathin two-dimensional van der Waals crystals opens up exciting prospects for exploring magnetism in the ultimate two-dimensional limit. Here, we show that environmentally stable CrSe nanosheets can be readily grown on a dangling-bond-free WSe substrate with systematically tunable thickness down to the monolayer limit. These CrSe/WSe heterostructures display high-quality van der Waals interfaces with well-resolved moiré superlattices and ferromagnetic behaviour. We find no apparent change in surface roughness or magnetic properties after months of exposure in air. Our calculations suggest that charge transfer from the WSe substrate and interlayer coupling within CrSe play a critical role in the magnetic order in few-layer CrSe nanosheets. The highly controllable growth of environmentally stable CrSe nanosheets with tunable thickness defines a robust two-dimensional magnet for fundamental studies and potential applications in magnetoelectronic and spintronic devices.