Antiferromagnetic interlayer correlations in annealedNi80Fe20/Ag multilayers

Sputtered ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$/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 ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$(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 ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$ 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 ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$ 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. © 1996 The American Physical Society.