Role of quantum confinement and interlayer coupling in CrI$_3$-graphene magnetic tunnel junctions

Recent demonstrations of magnetic ordering and spin transport in two-dimensional heterostructures have opened research venues in these material systems. In order to control and enhance the related physical phenomena, quantitative descriptions linking experimental observations to atomic details must be produced. Here we combine first principles and quantum ballistic transport calculations to shed important insights from an atomistic viewpoint on the underlying mechanisms governing spin transport in graphene/CrI$_3$ junctions. Descriptions of the electronic structure reveal that tunneling is the dominant transport mechanism in these heterostructures and help differentiate intermediate metamagnetic states present in the switching process. We find that quantum confinement and layer-layer interactions are key to describing transport in these two-dimensional systems. Ballistic transport calculations further support these findings and yield magnetoresistance values in remarkable agreement with experiments. The short width of these barriers limits analysis solely based on the bulk complex band structure often employed in the description of magnetic tunnel junctions. Our work devises mechanisms to attain larger tunneling magnetoresistances, proving valuable to the advancement of spin valves in layered heterostructures.