In-plane CrI₂/CrI₃ 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 CrI₂/CrI₃ in-plane heterostructure or superlattice can be obtained via deposition of Cr atoms on the CrI₃ monolayer. Our results show that CrI₂/CrI₃ superlattices are magnetic semiconductors with the magnetic order depending on the width of the CrI₂ ribbon. Interestingly, space charge separation exists in CrI₂/CrI₃ superlattices independent of the width of CrI₂ and CrI₃ ribbons. Under appropriate excitation, holes accumulate in the CrI₂ part of the superlattice and 100% spin polarized electrons accumulate in the CrI₃ part. A 3% tensile strain on the superlattice will induce a phase transition of the CrI₂ part. Nevertheless, the space charge separation in the CrI₂/CrI₃ superlattice occurs under tensile strain smaller than 6%. The tunable magnetic order and robust space charge separation indicate promising applications of CrI₂/CrI₃ superlattices in spintronic devices.