Thermally activated domain-wall motion in ferromagnetic single crystals

Abstract

For picture-frame-type single-crystal specimens of the ferromagnetic nickel-base alloy PE 16, the dependence of the domain wall velocity v on the applied magnetic field H and on temperature T has been experimentally investigated for 1.7<T<5 K. The results are interpreted by assuming that the domain wall can overcome the interaction with obstacles present in the specimen by thermal activation. Interaction potentials, which have been in common use for such problems, e.g., triangular ones, failed to give agreement between theory and experiment. Therefore a formalism has been developed, by which information on the interaction force, F (x), between the obstacle and the domain wall can directly be obtained from the experimental data. By using F (x), a relation H (v,T) can be reconstructed which is in perfect agreement with the experimental results. The obstalces, which interact with the domain wall, are probably single atoms or small clusters.

A phenomenological model of magnetisation kinetics

“…As in the mechanical case dAG(Hi)/dHi is related to U , the volume involved in the activation process (Siemers andNembach 1979, Street et a1 1987) and may be written as…”

“…The latter component is related at the microscopic level to the motion of dislocations. Siemers and Nembach (1979) developed this analogy and considered a model of thermally activated domain wall mobility using a number of plausible potential functions to describe the interaction of a domain wall with pinning centres. A more elaborate theory taking into account the statistical distribution of pinning centres and the flexibility of domain boundary walls was developed by Gaunt (1983) by analogy with statistical theories of dislocation motion through a random array of obstacles.…”