Magnetoresistance and negative differential resistance in Ni/graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study

Using the nonequilibrium Green's function formalism combined with density functional theory, we study finite bias quantum transport in Ni/Gr(n)/Ni vertical heterostructures where n graphene layers are sandwiched between two semi-infinite Ni(111) electrodes. We find that the recently predicted "pessimistic" magnetoresistance of 100% for n >= 5 junctions at zero bias voltage V-b -> 0 persists up to V-b similar or equal to 0.4 V, which makes such devices promising for spin-torque-based device applications. In addition, for parallel orientations of the Ni magnetizations, the n = 5 junction exhibits a pronounced negative differential resistance as the bias voltage is increased from V-b = 0 V to V-b similar or equal to 0.5 V. We confirm that both of these nonequilibrium transport effects hold for different types of bonding of Gr on the Ni(111) surface while maintaining Bernal stacking between individual Gr layers.