High frequency permittivity dispersion of Fe-based nanocrystallined ferromagnetic flakes

Abstract High frequency permittivity of Fe-based nanocrystalline flakes (Fe-Cu-Nb-Si-B) being milled for different hours have been studied. An inverse dependence of peak frequency on the static dielectric constant in dielectric loss spectra is found. The total dielectric loss also increases with milling time. The Havriliak-Negami model is used to study the permittivity dispersion behaviors. It reveals that both the symmetric and asymmetric broadening factors play roles in the deviation of the measured permittivity spectra from the Debye-type theoretical dispersion. The fundamental physics for the dispersion of permittivity is “Maxwell-Wagner-Sillars” interfacial polarization, which arises from the difference in the conductivity of two phases existing in the nanostructures of flakes.