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The full thickness-dependent electrical conductivity of polycrystalline NiO/Co/Cu/Co spin-valve structures was measured in situ during ion-beam deposition and compared with calculations based on realistic band structure. We have found striking features in the experimental conductivity which are unexpected from widely used semiclassical free-electron models. Addition of ∼ 1 ML Co to a NiO/Co/Cu surface causes the net film conductance to decrease; the reverse case of Cu on NiO/Co shows a strong positive curvature of the thicknessdependent conductance, indicating a reduction of the conductivity in Cu near the interface with Co. Quantitative agreement is found between the experimental thickness-dependent film conductance and multiband tightbinding model calculations using a single constant parameter for on-site atomic disorder. The experimental data are consistent with strong scattering of conduction electrons in Cu at the interfaces with Co. Comparison with theory suggests that most of the observed interface scattering may be considered to be intrinsic, arising from the placement of a high density of empty Co d states at the Cu boundaries.