Reduction of spin-flip scattering in metallic nonlocal spin valves

Cobalt-copper nonlocal spin valves are fabricated by shadow evaporation through nanoscale masks. The thickness of Co electrodes is varied and the spin diffusion length of the Cu channel is determined. Short spin diffusion lengths are found in devices with thick (>20nm) Co layers. Co impurities are introduced into the Cu channel in the shadow evaporation process during the fabrication, and the impurities cause spin-flip scattering. The amount of Co impurities can be reduced by decreasing the thicknesses of Co electrodes. Spin diffusion lengths of similar to 400 nm at 295 K and similar to 800 nm at 4.2 K are measured in devices with thin (<10 nm) Co layers. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3514204]