Domain wall resistance and magnetoresistance of narrow ferromagnetic wires

We report new experimental results for the transport properties of very narrow Ni wires. By suitable preparation with a magnetic field applied parallel to the axis of a wire it is possible to introduce domain walls, or to sweep all walls out of a sample. We find that domain walls make a contribution to the resistance which is negative. When a field is applied perpendicular to the axis of a wire, the resistance exhibits abrupt steps and hysteresis which suggest that rather modest perpendicular fields are able to nucleate domain walls, and enable us to measure the resistance of a single domain wall.