Specular reflection in spin valves bounded by NiO layers

We have experimentally investigated the possibility of increased electron reflectivity induced by an insulating NiO layer that is used to exchange bias a metallic spin-valve. For this purpose Ni₈₀Fe ₂₀/Cu/Ni₈₀Fe₂₀ and Ni₆₆Fe ₁₆Co₁₈/Cu/Co₉₀Fe₁₀ spin-valves were grown and subsequently covered by insulating NiO or by metallic FeMn. In all cases the giant magnetoresistance of the NiO spin-valves is systematically larger upon a variation of the exchange-biased ferromagnetic layer thickness, also after correcting the data for the conductivity of FeMn which we have determined from a separately grown series of samples with variable FeMn thickness. The increased giant magnetoresistance ratios can be qualitatively understood on the basis of a semiclassical calculation in which (partial) specular reflectivity at the NiO interface has been included