Correlation between giant magnetoresistance and the antiferromagnetic volume fraction in superlattices

We investigated the giant magnetoresistance (GMR) of metallic magnetic superlattices and its correlation to the volume fraction of antiferromagnetically aligned magnetic layers. It is assumed that the superlattices are composed of a mixture of regions having, respectively, antiferromagnetic and ferromagnetic alignments. The calculated correlation curves for Co/Cu and FeNiCo/Cu superlattices show good agreement with the experimental results. The upper limits of the GMR in these superlattices are predicted in the case of a perfect antiferromagnetic alignment. It is shown that the observed nonlinear behavior of correlations is attributed to the film quality of superlattices. By assuming the existence of different regions of ferromagnetic but antiparallel alignment, it is understood that the observed results of no GMR for small volume fraction are due to an apparent phenomenon. The GMR is analyzed from the point of view of the preparation conditions of superlattices. (C) 1996 American Institute of Physics.