Initial susceptibility frequency spectra and distribution of the grain sizes in Ni-Zn and YIG polycrystalline ferrites

Abstract

The influence of the non-homogeneity of grain sizes on the initial susceptibility as depending on the mean grain size and the frequency spectra in polycrystalline soft-ferrites is investigated. An estimation of the non-homogeneity of grain sizes is made based on the frequency dispersion of the initial susceptibility characteristics. The distributions of the grain sizes in Ni-Zn-Co, NiFe2O4 and YIG ferrites is measured. It is found that the coefficient a = (μ′max − μ′0)/μ′0 related to the (μ′ − 1)c = F(f) characteristics is proportional to the standard deviation of the grain size distribution σ, where the μ′max denotes the maximum value of the initial permeability in the frequency range of the domain walls resonance, μ′0 the initial permeability value existing below this frequency range, f the frequency, the index c = dx/d, where dx is the X = ray density and d the density of a given sample. This regularity is found to appear for the same number of maxima n for a given distribution. If the coefficient a is equal to zero there is no non-homogeneity of grain sizes. For a one-maximum distribution and for a < 0.2, the non-homogeneity of grain sizes has no influence on the (μ′ − 1)c = F(D) characteristics in the investigated ferrites (D is the mean grain size).