In-plane CrI 2 /CrI 3 2D superlattices: novel electronic properties and strain induced phase transition.

Two-dimensional (2D) magnetic materials show promising applications in spintronic devices. Heterostructures and superlattices play an important role in property tuning and device design. Vertical heterostructures of 2D magnets have been widely studied while the study of in-plane heterostructures is quite limited. Here, based on density functional theory, we propose that a perfect CrI 2 /CrI 3 in-plane heterostructure or superlattice can be obtained via deposition of Cr atoms on the CrI 3 monolayer. Our results show that CrI 2 /CrI 3 superlattices are magnetic semiconductors with the magnetic order depending on the width of the CrI 2 ribbon. Interestingly, space charge separation exists in CrI 2 /CrI 3 superlattices independent of the width of CrI 2 and CrI 3 ribbons. Under appropriate excitation, holes accumulate in the CrI 2 part of the superlattice and 100% spin polarized electrons accumulate in the CrI 3 part. A 3% tensile strain on the superlattice will induce a phase transition of the CrI 2 part. Nevertheless, the space charge separation in the CrI 2 /CrI 3 superlattice occurs under tensile strain smaller than 6%. The tunable magnetic order and robust space charge separation indicate promising applications of CrI 2 /CrI 3 superlattices in spintronic devices.