Reversal processes and domain wall pinning in polycrystalline Co-nanowires

The magnetization reversal process of single Co nanowires is investigated experimentally by magnetoresistance measurements at low temperatures. The results are compared to magnetic force micrographs of the remanent domain configuration. The theoretical expectation for the reversal process is obtained from Monte Carlo simulations. We find that both the width and the thickness of the wires as well as surface scattering play a significant role for the magnetization reversal processes. While thick (t > 15 nm) and narrow nanowires (w < 800 nm) switch by domain wall nucleation at the wire ends followed by wall motion, the magnetization reversal process in wide and/or thin nanowires is achieved by the generation of a multidomain state of the magnetization. It is shown both experimentally as well as theoretically that the wire width dependence of the coercive field can be used to pin a domain wall between two wire parts of different widths.