Novel Frequency Dispersion of Permeability in Nickel Ferrites with Different Amounts of Cobalt Doping

The effect of cobalt doping on permeability spectra of nickel ferrites with excess iron (Ni0.743-xMn0.057CoxFe2.20O4, x = 0-0.027) has been studied. With increasing amounts of Co-doping, the static permeability mu(i) decreases at first, then increases to the localmaximum at Co substitution of x = 0.018, and finally decreases again. The permeability spectra go through a modification of relaxation-resonance-relaxation dispersions. The samples with Co substitution of x = 0.018 and 0.021 have the static permeability of similar to 13, resonance frequency of 400 MHz, and sufficiently low magnetic loss tangents, over 1-250 MHz, make them promising candidates for high frequency applications.