Influence of Dy3+ and Cu substitution on the structural, electrical and dielectric properties of CoFe2O4 nanoferrites

In this work, Dy3+ and Cu doped cobalt ferrites with general chemical formula Co0.8−xDyxCu0.2Fe2O4 (where x = 0.0, 0.1, 0.3 and 0.5) have been synthesized via sol–gel route. The cubic phase confirmation and chemical bonding were revealed using X-ray diffraction and Fourier transform infrared spectroscopy respectively. Thermal stability of as-prepared samples was checked by thermo-gravimetric and differential thermal analysis. The surface morphology was studied by scanning electron microscopy. Raman spectroscopy was used for further confirmation of the single-phase cubic spinel structure of the samples. The average crystallite size was found to decrease from 17.5 to 12.4 nm and the lattice constant was increased from 8.3564 to 8.3811 A on incorporation of Dy3+ ions. The dc electrical resistivity in the temperature range of 303–393 K shows the semiconducting nature of the as-prepared samples. The activation energies for different samples were estimated from the Arrhenius plot and found to be in range of 0.25–0.30 eV. The dielectric constant (e′), ac conductivity (σac) and dielectric loss (tanδ) have been analyzed in the frequency range of 42 Hz - 5 MHz at room temperature. All the dielectric parameters were found to decrease on adding Dy3+ ions. The variation of dielectric properties e′, tanδ, and σac with frequency indicates the typical Maxwell–Wagner type dielectric behavior due to interfacial (space charge) polarization and the exchange of electrons among Fe2+ and Fe3+ ions. Electron paramagnetic resonance measurements of as-prepared ferrite nanoparticles show the weak super-exchange interactions which cause the large g-value and broadening of the resonance line as compared to the free electron g-value. The prepared ferrites have high dielectric permittivity and low loss making them promising materials for the applications in high frequency memory storage devices.