High frequency electrical transport properties of CoFe₂O ₄ and Sr₂NiMnFe₁₂O₂₂ composite ferrites

Composite ferrite ceramic materials were obtained by mixing sol/gel derived CoFe₂O₄ and Sr₂NiMnFe₁₂O ₂₂ nanopowders sintered at 1050 C for 3 h. The synthesized samples were characterized by XRD, Scanning Electron Microscopy, FT-IR, electrical resistivity and dielectric measurements. XRD analysis revealed that there is no new phase observed, indicating that no chemical reaction occurs between spinel and hexagonal phases and the intensity of Y-phase gradually decreased by increasing spinel concentration. Crystallite size calculated from XRD data decreased by increasing spinel concentration. Room temperature resistivity and activation energies of the samples increased with increasing spinel concentration. Dielectric constant of pure Y-type hexagonal ferrite decreased by increasing spinel concentration up to ~8.5. At higher frequency further decrease in dielectric constant was observed due to Maxwell-Wagner type relaxation with few resonance peaks beyond 2 GHz. Imaginary part of dielectric constant showed the similar behavior with frequency. Low dielectric constant, low dielectric losses and high resistivity make these composite ferrites useful in electromagnetic attenuation materials and microwave devices.