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

Using the nonequilibrium Green function formalism combined with density functional theory, we study finite-bias quantum transport in Ni|Grn|Ni vertical heterostructures where n graphene layers are sandwiched between two semi-infinite Ni(111) electrodes. We find that recently predicted “pessimistic” magnetoresistance of 100% for n ≥ 5 junctions at zero bias voltage Vb → 0, persists up to Vb ' 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 Vb = 0 V to Vb ' 0.5 V. We confirm that both of these nonequilibrium effects hold for different types of bonding of Gr on the Ni(111) surface while maintaining Bernal stacking between individual Gr layers.