X-ray resonant magnetic scattering study of the magnetic coupling in Co/Pt nanolines and its evolution under magnetic field

Periodic arrays of silicon nanolines, covered by a Co/Pt multilayer, with perpendicular magnetization, have been studied by soft x-ray resonant magnetic scattering at the Co L-3 edge. At the resonance, magnetic signals appear both on top of the structural diffraction peaks, characteristic of the grating, and between these peaks. These superstructure satellites reveal an antiferromagnetic order, generated by the interline dipolar coupling. Their intensities are strongly sensitive to the magnetic history, and can be enhanced through specific demagnetization processes. By applying an in situ magnetic field, the evolution of the magnetic signal has been monitored through the entire hysteresis loop. The magnetic contribution of the structural superlattice peaks can be quantified by their asymmetry ratio, whose angular variation stems from the scattering factor. The change of the purely magnetic satellites with the magnetic field is completely reproducible and characterizes the modifications of the magnetic configuration during the reversal process. A model of Ising macrospins, from which the distribution of the magnetic reversal fields can be deduced, is shown to be in agreement with the measured results.