The diameter dependent magnetoresistance of a single Ni nanowire (i.e. 200 and 30 nm diameter) bridging microfabricated Ni electrodes was investigated at temperatures ranging from 10 to 300 K. Overall, the magnetotransport behaviour of single Ni nanowires was similar to the results for thin films, except that the magnitudes of transverse magnetoresistance and longitudinal magnetoresistance differed from the values for thin films when the diameter of the nanowire was small. The difference might be attributed to a change in the stress anisotropy of the nanowire from a tensile stress induced by a thermal expansion mismatch between the nanowire and the Si substrate or different magnetocrystalline anisotropy. Based on the angle dependent switching field, the magnetization reversal mechanism of 30 and 200 nm nanowires at 10 K was determined to be the curling mode, and the size of the curling nucleation is smaller than the diameter of the nanowire.
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