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. © 2006 The American Physical Society.