Magnetoresistance of carbon-covered Co nanowires

We have investigated the magnetoresistance of carbon-coated Co nanowires with various widths down to w=32 nm at low temperatures (T=4.2 K). The nanowires and their non-magnetic contact pads are prepared by means of a three-step electron beam lithography (EBL) process in a LEO secondary electron microscope. We obtain wires with highest quality by using specifically customized resist systems with undercut. The longitudinal magnetoresistance shows pronounced features at the coercive fields Hc-where Hc increases with decreasing wire width as 1w-indicating a magnetization reversal process accomplished by domain nucleation and traversal. In contrast, the transverse and perpendicular magnetoresistance continuously decrease to their saturation values which can be understood in terms of a coherent rotation of the magnetization using the anisotropic magnetoresistance.