Dragging of domains by an electric current in ferromagnetic bulk cobalt at 4 K

The electrical resistivity of cobalt single crystals of high purity has been measured for current densities j up to 400 A/mm2, at 4.2 K. Large deviations from Ohm’s law are observed when j exceeds ≃12 A/mm2, in agreement with theoretical predictions. The electron gas in translation exerts hydromagnetic forces on the domain walls. The deviations from Ohm’s law happen when these forces are large enough to overcome the pinning forces and to set the walls in motion, in a direction parallel to the drift speed of the charge carriers. The dragging forces also tend to reorient the walls in a direction parallel to the current. Magnetic fields parallel to the current are used to minimize this reorientation.