Structural, AC conductivity, impedance and dielectric study of nanocrystalline MFe₂O₄ (M = Mg, Co or Cu) spinel ferrites

Nanocrystalline MFe₂O₄ (M = Mg, Co or Cu) spinel ferrites were prepared using novel combustion method and its structural, AC conductivity, impedance and dielectric properties were investigated. The powder X-ray diffraction analysis shows that the size and lattice constant of nanocrystalline MgFe₂O₄, CoFe₂O₄ and CuFe₂O₄ are 10.4, 28.6 and 9.6 nm (8.330, 8.369, and 8.342 Å), respectively. Further the Raman spectra confirm the spinel phase formation and five active Raman modes such as 1A_1g, 1E_g, 3T_2g are assigned for each ferrite. The Fourier transform infrared spectra confirms the formation of tetrahedral and octahedral sites. The electrical properties such as AC conductivity, impedance, dielectric constant and tan δ are reported. The value of AC conductivity at 30 °C (at 1 Hz) is 1.12 × 10⁻⁸, 1.91 × 10⁻¹⁰ and 9.19 × 10⁻⁸ S/cm, respectively for MgFe₂O₄, CoFe₂O₄ and CuFe₂O₄ ferrites. The activation energy of AC conductivity process, calculated using Arrhenius relation is ranged from 0.45 to 0.56 eV. The impedance analysis shows that the contribution of grain boundary is more than that of grain for the electrical behavior of the prepared samples. The dielectric study shows that the CoFe₂O₄ has the lowest value of dielectric constant and tanδ among the three investigated samples.