Magnetic instabilities in thin non-planar ferromagnetic films

Lorentz microscopy images of thin permalloy films reveal the presence of vortices stabilised by a normal magnetic field. The vortex structures are also accompanied by a complex domain wall pattern which is nucleated by the external field and is believed to be related to the shape anisotropy of the system. The non-planar nature of the film investigated is, in fact, the necessary condition for the observation of such phenomena. Through the interpretation of the micrographs, we analyse the energetics of the system by formulating a magnetic model which encapsulates the shape anisotropy of the sample. We show that the external field can induce instabilities in the system and the parameters estimated through our model are consistent with the experimental values.