Domain Rotation in Nickel Ferrite

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Abstract
An experiment has been performed which leads to the conclusion that the initial permeability and radio-frequency dispersion in sintered nickel ferrite are due principally to rotation of crystallite magnetic moments in an equivalent anisotropy field. Samples have been prepared by the partial sintering of nickel ferrite particles of size 0.5 to 1.0 micron. For a series of samples sintered to various maximum temperatures, complete permeability spectra have been obtained, and it has been found that the susceptibility at low frequencies is related to the resonant frequency of the dispersion, defined as the point where susceptibility reduces to one-half its low-frequency value, in a manner which is predictable from the theory of domain rotation. Significant contribution from domain wall motion is probably inhibited by the small grain size in the samples studied. Our results do not preclude the existence of domain wall motion as a significant phenomenon in the behavior of certain ferrites, but indicate the importance of polycrystalline structure in determining the mechanism of initial polarization.

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