Nonuniform current distribution in the neighborhood of a ferromagnetic domain wall in cobalt at 4.2 K

Abstract

It is shown theoretically and experimentally that the current density is not uniform in the neighborhood of a 180 ° domain wall, in a pure ferromagnet traversed by an electric current at low temperature. The effect is caused by the abrupt reversal of the internal field B=Ms across the wall, and by the corresponding gradual reversal of the Hall electric field. In a noncompensated ferromagnetic metal (Co, Ni) in the high field limit ωcτ≫1, domain walls would act as if they were electrically insulating; the current could cross the wall only through a small ``hole'' located at one end of the wall, creating an infinite current density there. A cobalt single crystal of limited purity (R300/R4.2 = 65) was cut in the shape of a thin slab normal to the c axis. One-half of the slab is magnetized to saturation in the c direction and the other half is magnetized in the opposite direction, thus simulating one domain wall. When a dc current crosses the wall, the current density is found to be larger at one end of the wall than at the other end in a ratio of 1.7, in agreement with predictions. Current density is monitored locally with pairs of voltage probes. The magnitude and sign of the effect is consistent with ωcτ = 0.18 and electronlike carriers.