MAGNETIC DOMAIN STUDIES USING PERMEABILITY SPECTRA I

Measurements of the frequency spectrum of the complex reversible permeability of ferromagnetic metals are evaluated as a source of information about the general features of the magnetic domain structure, especially its dynamic aspects. Such information provides a valuable complement to essentially static visual observations of particular surface domain structures. Comparison of the measured spectra with the predictions of a simple but widely applicable model domain structure achieves (i) the separation of the contributions to the reversible permeability from domain wall displacement and coherent domain rotation, (ii) a measure of the average separation of active domain boundaries, and (iii) estimates of the mean and range of distribution of domain wall surface susceptibilities. The validity of this technique, its scope and its limitations, have been investigated using several magnetic materials with well-defined but very different domain structures. The internal consistency of the conclusions drawn, together with the good correlation between these conclusions and independent knowledge of the domain structures of these materials, testify to the essential correctness of the method.