A brief review of the domain wall (DW) response of polycrystalline ferrites, when subjected to AC excitation fields, is given. When the AC field frequency attains the limiting frequency where DW are able to follow the field, ferrites tend to show a complex dispersion that is a mixture of relaxation and resonance. The effect of microstructure (namely grain size distribution) is analyzed on NiZn ferrites with varying contents of V_2O_3 as additive. The results obtained show that a tight grain size distribution leads to clearer resonant character, while a wide distribution results in a mixed dispersion.
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