Nature of the interlayer coupling in annealed Ni₈₀Fe₂₀/Ag multilayers

Using x-ray and polarized neutron (PNR) reflectivity, we have measured the structural and magnetic depth profiles of annealed Ni₈₀Fe₂₀ (20 Å)/Ag (40 Å) multilayers. The x-ray data indicate that the interfaces are highly mixed. PNR measurements of the 335 °C annealed multilayer in small magnetic fields reveal a broad feature in the off-specular spin-flip scattering that is not present for the unannealed sample. The giant magnetoresistance is thus associated with antiferromagnetic correlations between micrometer-sized magnetic domains within the Ni₈₀Fe₂₀ layers. This spin ordering is consistent with a model in which weak dipolar forces lead to an antiparallel alignment of the domains across the Ag layers.