Evolution of stripe and bubble domains in antiferromagnetically coupled [(Co/Pt)8/Co/Ru]18 multilayers

The magnetization process of antiferromagnetically coupled [(Co/Pt)(8)/Co/Ru](18) multilayers with perpendicular anisotropy is investigated via magnetic force microscopy at room temperature by imaging the domain configuration in magnetic fields. In the zero-field state, due to the perpendicular anisotropy, stripe domains characteristic for ferromagnetic coupling are observed. By increasing the external magnetic field, the domain configuration first modifies gradually, then transforms from continuous into isolated stripes, and changes in the end into bubbles, which collapse at higher fields. A theoretical model previously developed for bubble domains in single layer films is adapted for arbitrary complex multilayers and applied to the present layer architecture. The calculated values for strip-out and collapse fields compare well with the experimental results and demonstrate the validity of the theoretical description.