Soft x-ray magnetic scattering evidence for biquadratic coupling in Co/Cu multilayers

Soft x-ray resonant magnetic scattering has been used to study the magnetic structure of sputtered Co/Cu multilayers. A pure magnetic peak, at half the scattering vector of the structural Bragg peak from the multilayer, was observed from layers with and without deliberate oxygen contamination in the middle of the copper spacer layer. With increasing field in the sample plane, the magnetic peak intensity varied very differently for the two types of sample due to the high sensitivity of the magnetic scattering to changes in moment rotation in the sample plane. The data provide strong support for a model of biquadratic coupling in the contaminated samples and bilinear, antiferromagnetic coupling in the clean samples