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 semi-conductor, 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.