Proximity induced exchange coupling in a Phosphorene heterojunction with CrI₃ substrate: a first-principles calculation

The two-dimensional (2D) van der Waals (vdW) materials offer a platform to design heterojunctions in various stacking orders to create different functionalities at an atomically thin thickness [1]. Recently, the family of 2D ferromagnetic materials [2, 3, 4] has emerged as a new field of research, which violates the Mermin-Wagner theorem, and their exciting electron charge and spin behavior offer potential for spin devices. In this study, we have systematically investigated the electronic and magnetic behavior of phosphorene - CrI₃ (P/CrI₃) heterojunction through the first-principles based density functional theory (DFT) calculations. We built the heterojunction by using a single layer of black phosphorene with magnetic substrate 2D CrI₃ by weak vdW force, where the average relaxed interlayer distance is 3.51Å [5]. The result indicates that the valence and conduction bands near the Fermi level are localized in different monolayers of P/CrI₃ heterojunction, where the energy gap of heterojunction is reduced from that of the monolayers of black phosphorene and CrI₃. The intrinsically nonmagnetic phosphorene layer [6] is also magnetized and enhances the magnetic anisotropy energy of the CrI₃ substrate in heterojunction. In addition, we demonstrate perfect spin filtering by spin injection from a ferromagnetic substrate to a phosphorene layer. These results help in a fundamental understanding of the 2D heterojunctions and are of significant importance for CrI3-based spintronic devices.