Magnetic domains in construction steel

The magnetic domain structure in constructional steel has been studied using a ferrofluid technique. We observed domains of four types which have been described and classified. A correlation is observed between the type of domain structure and grain size. For a simple antiparallel domain structure, a relationship exists between the grain size and domain wall spacing. The coefficient characterizing the magnetic interaction between grains is suggested, and a model is proposed which gives a linear relation between sqrt (domain length) and domain wall spacing. This model gives us a reasonable agreement with experiment and is compared with the results obtained using different models. The size of a single-domain grain was also estimated using the suggested model.