Analysis of measured transport properties of domain walls in magnetic nanowires and films

Existing data for soft magnetic materials of critical current for domain-wall motion, wall speed driven by a magnetic field, and wall electrical resistance show that all three observable properties are related through a single parameter: the wall mobility μ. The reciprocal of μ represents the strength of viscous friction between domain wall and conduction-electron gas. And μ is a function of the wall width, which depends in turn on the aspect ratio t∕w, where t and w are the thickness and width of the sample. Over four orders of magnitude of μ, the data for nanowires show μ∝(t∕w)^−2.2. This dependence is in approximate agreement with the prediction of the 1984 Berger theory based on s-d exchange. On the other hand, it is inconsistent with the prediction of the 2004 Tatara and Kohno theory, and of the 2004 Zhang and Li theory.