Model for Reverse-Domain Nucleation in Ferromagnetic Conductors

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Abstract
Recent reports indicate that the average dynamic domain size in a material undergoing a change in magnetization may be significantly smaller than the static domain size. This finer dynamic domain structure can be predicted by an application of the principle of minimum entropy production Eddycurrent dissipation and dissipative domain nucleation and annihilation processes are considered as the dominant mechanisms for entropy production. Expressions for their contributions are derived and the total entropy production is minimized with respect to the density of domains. The theoretical average domain width thus derived is found to vary with frequency as (f)−1/2 and with peak induction as (Bmax)−1, in accord with observations. A comparison of the theoretical with observed domain densities permits an evaluation of the dissipation per unit wall area associated with the dynamic process of nucleating a reverse‐domain wall. This energy is an order‐of‐magnitude larger than domainwall surface energy.