Antiferromagnetic interlayer correlations in anneale/Ag multilayers

Sputtered (Formula presented)(Formula presented)/Ag multilayers, annealed post-growth, exhibit giant magnetoresistance (GMR) with pronounced field sensitivity [T. L. Hylton et al., Science 261, 1021 (1993)]. We have characterized a series of (Formula presented)(Formula presented)(20 Å)/Ag(40 Å) multilayers annealed at temperatures ranging from 305 to 335°C using x-ray and polarized neutron reflectivity techniques. For all of the samples, specular x-ray measurements reveal that the laterally averaged interfaces between the (Formula presented)(Formula presented) and Ag layers are not well defined. The growth-plane morphology of the multilayers, determined from off-specular x-ray diffraction, shows a dependence on annealing temperature. Specular and off-specular polarized neutron reflectivity data indicate that the GMR in the annealed samples does not arise from long-range antiferromagnetic alignment of coherent ferromagnetic sheets, as generally observed in related materials. Instead, annealing promotes the formation of planar ferromagnetic domains of micrometer size within each (Formula presented)(Formula presented) layer that are antiferromagnetically correlated along the growth axis. The length scales of these domains are consistent with a model in which weak dipolar forces dominate the interactions between them.