Structural, dielectric and complex impedance properties of T0.6Co0.4Fe2O4 (T=Ni, Mg) ferrite nanoparticles prepared by sol gel method

Spinel ferrites T0.6Co0.4Fe2O4 (T= Ni, Mg) were prepared by Pechini sol-gel technique at 1323 K. The X-ray diffraction results indicate that the ferrite samples have a cubic spinel type structure with Fd (3) over barm space group. FTIR showed two absorption bands (v(1) and v(2)) that are attributed to the stretching vibration of tetrahedral and octahedral sites. The electrical properties of the studied samples using complex impedance spectroscopy technique have been investigated in the frequency range 40 Hz - 10(7) Hz and in the temperature range 200 - 420 K. The total conductivity curves for samples are found to obey Jonscher power law sigma(omega) =sigma(dc) +A omega(n) with an increase of the frequency exponent (n) as temperature increases. The effect of frequency, temperature and composition on dielectric constant (epsilon') and dielectric loss (tan delta) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. Activation energy has been estimated from both temperature dependent of de conductivity and relaxation time data, which indicates that same kinds of charge carriers are governing both the processes. Nyquist plots of impedance show semicircle arcs for samples and an electrical equivalent circuit of the type of R-g+(R-gb//Z(CPE)) has been proposed to explain the impedance results.