Giant magnetoresistance and Co-cluster structure in phase-separated Co-Cu granular alloys

We examine the effect of Co-cluster morphology on giant magnetoresistance (MR) in phase-separated Co-Cu films. The Co clusters were characterized through grazing incidence, anomalous, small-angle x-ray scattering. With thermal annealing the Co cluster diameter increases from 21 to [similar to]250 A with a concomitant drop from [similar to]35% to 1% in the 4.2 K MR. The MR scales approximately as the inverse cluster size. Comparison with theory indicates that interfacial spin-dependent electron scattering is the dominant scattering mechanism underlying giant MR for cluster diameters up to at least 250 A.