Galvanomagnetic voltages in the vicinity of a domain wall in ferromagnetic thin films

Ferromagnetic Ni-Fe films of thickness <85 nm contain Néel or crosstie walls, with wall thickness as large as 6 μm. Because of the anisotropic magnetoresistance Δρ/ρ0≂2% in Ni-Fe, the electrical resistivity is slightly larger inside a wall than in the adjacent domains, for currents normal to the wall. This should result in a detectable increase dV of the ohmic voltage between two miniature potential probes when a wall is located between them. For reasonable values of the dc current density, our calculations predict dV≂9 μV per wall. When the current is parallel to Néel walls, there should be a local decrease of the resistivity inside each wall, manifested as a decrease of the average sample resistance. This effect seems to provide an explanation for the upward resistance jumps observed in Ni-Fe magnetoresistive reading heads when Néel walls disappear. Also, because of the planar Hall effect, a voltage V should appear between two potential probes when one probe is located at the wall center.