Delocalized versus localized magnetization reversal in template-grown Ni and Ni80Fe20 nanowires

The study of magnetization reversal processes of highly ordered magnetic nanowire arrays is of particular interest due to their potential application as perpendicular recording media. We electrodeposited high-aspect ratio Ni and Ni80Fe20 nanowires in nanoporous alumina templates and performed SQUID measurements as a function of temperature (5-350 K) in order to better understand the magnetization reversal mechanisms active in our arrays. A strong coercive field deviation from the expected theoretical value calculated from the Stoner-Wolfarth model assuming delocalized magnetization reversal processes was observed. To explain our results, we then assumed a magnetization reversal triggered by thermal activation over an energy barrier. Taking into account the measured effective anisotropy, obtained experimentally from a low-field susceptibility approximation, we extracted the activation volume and found it to be much smaller than the nanowire physical volumes. This lead us to conclude that domain nucleation was present, mainly due to imperfections that introduce different local anisotropies and thus domain wall nucleation sites.