I - V asymmetry and magnetoresistance in nickel nanoconstrictions

We present a joint experimental and theoretical study on the transport properties of nickel nanoconstrictions. The samples show highly non-linear and asymmetric I-V characteristics when the conductance is smaller than G ₀ = 2e²/h, and huge magnetoresistance ratios exceeding 99.9%. We model a single point contact in a two-band tight-binding model as a 2 × 2 nickel chain connected to two semi-infinite nickel leads. The magnetoresistance is calculated by using a non-equilibrium Green's function technique.