Spin Filtering in CrI₃ Tunnel Junctions

The recently discovered magnetism of two-dimensional (2D) van der Waals crystals has attracted a lot of attention. Among these materials is CrI₃, a magnetic semiconductor, exhibiting transitions between ferromagnetic and antiferromagnetic orderings under the influence of an applied magnetic field. Here, using first-principles methods based on density functional theory, we explore spin-dependent transport in tunnel junctions formed of face-centered cubic Cu(111) electrodes and a CrI₃ tunnel barrier. We find about 100% spin polarization of the tunneling current for a ferromagnetically ordered four-monolayer CrI₃ and a tunneling magnetoresistance of about 3000% associated with a change of magnetic ordering in CrI₃. This behavior is understood in terms of the spin and wave-vector-dependent evanescent states in CrI₃, which control the tunneling conductance. We find a sizable charge transfer from Cu to CrI₃, which adds new features to the mechanism of spin filtering in CrI₃-based tunnel junctions. Our results elucidate the mechanisms of spin filtering in CrI₃ tunnel junctions and provide important insights for the design of magnetoresistive devices based on 2D magnetic crystals.