Tunneling of domain walls in ferromagnetic materials

For picture-frame-type specimens of various ferromagnetic alloys, the dependence of the domain wall velocity v on the external magnetic field H and on temperature T has been experimentally investigated. T ranged from 1.4 to 5 K and v from 1 to 106 μm/s. For four alloys, v varied exponentially with H and T. A model has been developed which describes the function v(H,T) found experimentally. The basic assumptions of this model are: (i) v is governed by the interaction of the domain wall with small obstacles present in the specimen. (ii) These obstacles can be overcome by a combination of two processes: thermal activation and tunneling. The experimental data are in excellent agreement with this model. Below 2.0 K, v is nearly exclusively governed by tunneling. The obstacles, which pin the domain walls, are probably small clusters of atoms.