Dielectric properties of nanocrystalline Co-Mg ferrites

Nanocrystalline powder samples with chemical formula CoxMg1-xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been synthesized by sol-gel auto combustion method using citric acid as fuel agent. The rietveld refinement study of x-ray diffraction patterns confirmed the spinel single phase formation for all samples. Dielectric constant (epsilon'), dielectric loss tangent (tan delta) and AC conductivity of CoxMg1-xFe2O4 ferrite nanoparticles have been measured at room temperature in the frequency range from 1000 Hz to 120 MHz. The dielectric dispersion observed at lower frequency region is attributed to Maxwell-Wagner two layer model, which is in agreement with Koops phenomenological theory. The observed results have been explained by polarization which is attributed to the electron exchange between Fe2+ and Fe3+ ions. The temperature variation of epsilon' and tan delta for some particular frequencies were studied. The rapid increase in epsilon' and tan delta has been explained using thermally activated electron exchange between Fe2+ <-> Fe3+ and Co2+ <-> Co3+ ions at adjacent octahedral sites. The role of interfacial polarization has been focused to explain the high dispersion in epsilon' and tan delta with temperature observed at low frequencies. (C) 2015 Elsevier B.V. All rights reserved.