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Magnetoresistance of Co/Cu superlattices grown by molecular beam epitaxy.

The giant magnetoresistance (GMR) has been investigated for Co/Cu superlattices grown by molecular beam epitaxy (MBE) with the copper and cobalt (111) planes parallel to the surface. When Au was used as a buffer layer, values of the GMR were found as high as 30%. Oscillations were observed in the saturation magnetic field as a function of the thickness of the Cu layer, but these oscillations were not observed in the GMR. The central purpose of the investigation was to study the effect on the GMR of annealing the superlattices and to interpret the changes in terms of the relative contributions to the resistivity of bulk and interface electron scattering. It was found that the magnitude of the GMR for the Co/Cu system decreases on annealing in sharp contrast to previous observations in Fe/Cr superlattices for which several workers have shown that the effect of annealing was normally to increase the GMR. This striking difference between the two systems is explained in terms of their very different spin dependence for interface electron scattering. A calculation is presented which accounts quantitatively for both our results for the Co/Cu system, and for the contrasting results in Fe/Cr.