Self-organized surface ripples as a source of magnetic anisotropies

In thin film magnetism surface and interfacemorphologies are important sources of magnetic anisotropy. This can be either due to the reduced coordination of step edge atoms (intrinsic contribution) or due to magnetic stray fields emanating from the film corrugation (extrinsic contribution). Low energy ion erosion is perfectly suited to create a periodic surface modulation (so-called ripples) on the nanoscale. By changing the primary energy of the ions the ripple periodicities can be varied from 20 to 150 nm. Subsequently, thin magnetic films are deposited on these template systems in order to investigate the influence of the surface morphology on the induced magnetic anisotropies. For small ripple periodicities a strong uniaxial magnetic anisotropy is found which rapidly decrease for larger ripple periodicities. In the case of Permalloy (Ni81Fe19) the induced anisotropy can be more than a factor of 20 larger compared to the intrinsic anisotropy of flat Permalloy. The microscopic origin of this effect will be discussed.