Magnetic behavior of systems composed of coupled ferromagnetic bilayers with distinct anisotropy directions

A shift in the hysteresis loop of a NiFe thin film (with in-plane anisotropy) exchange coupled to a [Pt/Co] multilayer (with out-of-plane anisotropy) is observed after in-plane saturation of the system. The origin of this effect and the related magnetic properties are investigated by means of in-plane and out-of-plane magnetometry techniques, magnetic force microscopy imaging, and micromagnetic simulations. Both the number of Pt/Co repetitions in the multilayer and the NiFe thickness are found to have an influence on the magnitude of the loop shift and the in-plane and out-of-plane coercivity values of the system. This is correlated with variations in the number and average size of the magnetic domains formed in the [Pt/Co] multilayer which, as revealed by micromagnetic simulations, pin the NiFe magnetization via formation of closure domains with a preferential orientation at the interface between the [Pt/Co] multilayer and the NiFe.