Domain structure and magnetization reversal of antiferromagnetically coupled perpendicular anisotropy films

We describe experimental and theoretical investigations of the magnetic domain formation and the field reversal behavior in antiferromagnetically coupled perpendicular anisotropy multilayers that mimic A-type antiferromagnet (AF) structures. The samples are sputter deposited Co/Pt multilayers with perpendicular anisotropy that are periodically interleaved with Ru to mediate an antiferromagnetic interlayer exchange. This structure allows precise tuning of the different magnetic energy terms involved. Using various magnetometry and magnetic imaging techniques as well as resonant soft X-ray scattering we provide a comprehensive study of the remanent and demagnetized configurations as well as the corresponding reversal mechanisms. We find that adding AF exchange to perpendicular anisotropy system alters the typical energy balance that controls magnetic stripe domain formation, thus resulting in two competing reversal modes for the composite system. In the AF-exchange dominated regime the magnetization is ferromagnetically ordered within the film plane with the magnetization of adjacent layers anti-parallel thus minimizing the interlayer AF exchange energy. In the dipolar dominated regime the magnetization pattern forms ferromagnetic (FM) stripe domains where adjacent layers are vertically correlated, but laterally anti-correlated thus minimizing the dipolar energy at the expense of the AF interlayer coupling. By tuning the layer thickness or applying a magnetic field, we observed the co-existence of AF domains and FM stripe domains. We find that a FM phase exists at AF domain boundaries, causing complex mesoscopic domain patterns with surprising reversibility during minor loop field cycling.