Since the direct observation of magnetization reversal processes in nanostructured systems is hard to achieve, we use magnetoresistance measurements as an indirect sensing tool. To avoid dipolar interactions present in nanowire gratings individual $\mathrm{Co}$ nanowires are prepared by electron beam lithography on $\mathrm{Si}$ substrates. Using a special two step process nonmagnetic gold contacts are attached to the $\mathrm{Co}$ nanowires to exclude an influence of the contact structures on the magnetization reversal process. To support the magnetoresistance analysis also the structure and morphology as well as the magnetic properties of the $\mathrm{Co}$ nanowires have been characterized using various microscopy and measurement techniques. Depending on the direction of the applied field three different magnetoresistance measurements can be distinguished. Based on the anisotropic magnetoresistance effect the transversal and the polar magnetoresistance reflect a coherent rotation of the magnetization independent of the wire width. In contrast, the longitudinal magnetoresistance shows a wire widths dependence of the magnetization reversal processes. In small wires nucleation processes occur whereas in wide wires the formation of complex domain structures has been observed. Nanowires with a width in between these groups show “transition”-like reversal processes.

• Received 10 September 2004

DOI:https://doi.org/10.1103/PhysRevB.71.064411