Effects of impurity atoms on sputtered GMR multilayers

We have investigated the effects of residual gas impurity atoms on interlayer exchange coupling and giant magnetoresistance (GMR) in Co(9Å)/Cu(9Å) multilayers. Structural analysis was performed by Co⁵⁹ NMR. We deposited sub-monolayer quantities of residual gases at different points in the Co/Cu bilayer; the interfaces, or the middle of the Cu spacers or Co magnetic layers. Impurities at the interface lower the GMR and increase remanent fraction and saturation field. We are able to model these results phenomenologically by adding biquadratic coupling. Impurities in the bulk of the Cu layers lower GMR still further, and such samples are well described by models containing almost 100% biquadratic coupling. We have demonstrated that the transport parameters in our samples are largely unaffected by small quantities of impurities, but that the interlayer coupling is extremely sensitive to them, particularly in the bulk of the Cu spacer layers