Significant tunneling magnetoresistance and excellent spin filtering effect in CrI-based van der Waals magnetic tunnel junctions.

van der Waals (vdW) heterojunctions stacked by different two-dimensional (2D) layered materials not only exhibit the complementary effect of short plates, but also harbor novel physical phenomena. In particular, the emergence of 2D magnetic vdW materials has provided novel opportunities for the application of these materials in spintronics. However, to the best of our knowledge, to date, the spin-related transport mechanism in magnetic tunnel junctions (MTJs) based on these 2D vdW magnetic materials and the effect of pinning layers on their transport properties have not been elucidated by the non-equilibrium state theory. Herein, based on first-principles calculations, we report the spin-polarized quantum transport properties of sandwich-type vdW magnetic tunnel junctions (CrI3/h-BN/n·CrI3) comprising monolayer CrI3, a hexagonal boron nitride (h-BN) spacer layer, and n-layer CrI3 (n = 1, 2, 3, and 4). Considering the inter-layer antiferromagnetic coupling in n-layer CrI3, a few layers of CrI3 can be regarded as its own natural pinning layers. Especially, when n is equal to 3, an almost fully spin-polarized current and large tunnel magnetoresistance ratio (3600%) are obtained in the equilibrium state. Excitingly, due to different numbers of pinning layers in MTJs, the transport properties of these MTJs at positive bias voltages exhibit an interesting odd-even effect within a limited thickness of these pinning layers. Moreover, an almost perfect spin filtering effect and remarkable negative differential resistance (NDR) were observed in the MTJs where n was odd (n = 1 and 3). The observed non-equilibrium quantum transport phenomenon is explained by spin-dependent transmission coefficient at different bias voltages. Our results provide effective guidance for the experimental studies of the MTJs based on 2D magnetic vdW materials.