Magnetic domain studies using permeability spectra - II: iron and silicon iron

The magnetic permeability of a number of specimens of iron and silicon iron, differing in grain size and heat treatment, has been measured over the range 500 Hz to 30 MHz; measurements were made on thermal and ac demagnetized states and in polarizing fields extending well beyond the knee of the magnetization curve. The measured dispersion of permeability, ascribed to eddy currents, has been analysed in terms of a simple but general domain model as in a previous paper by Collar et al. Consistent values of the rotational contribution to the permeability have been extracted from the measurements which are shown to be in quantitative agreement with theory provided due allowance is made for magnetic interactions between crystallites. There is found to be only a weak dependence of domain wall susceptibility upon grain size; the restoring force on a domain wall must therefore be caused primarily by metallurgical conditions within the crystal grains rather than by any direct influence of the grain boundaries.