SYNTHESIS AND CHARACTERISATION OF STRUCTURAL, MAGNETIC AND ELECTRICAL PROPERTIES OF CO-BASED SPINEL FERRITES

The effects of zinc, nickel, zirconium and aluminum on the cobalt based spinel ferrites nanoparticles are investigated. Four series of spinel Co-ferrites with nominal compositions Co1-xZnxFe2O4 (x=0.0-0.6), Co1-xNixFe2O4(x =0.0-0.5), CoFe2-2 xZrxZnxZ4 (x = 0.0-0.4) and CoFe2-xAlx04 (x= 0.00-0.50) respectively, were prepared by the chemical co-precipitation method. The samples were characterized by X-ray diffraction, low field AC magnetic susceptibility, DC electrical resistivity and dielectric properties measurements. The average crystallite sizes were calculated from the indexed XRD diffraction peaks using the Scherrer formula. The average crystallite sizes of precipitated particles lie within the range 14-23 nm, 17-23 nm, 21-27 nm and 13-20 nm, respectively.\ud \ud The Curie temperature was obtained from AC magnetic susceptibility measurements in the range 77 K to 850 K. It is observed that Curie temperature decreases with the increase of Zn, Zr, Al and increases with Ni concentration for all the samples. The variation of Curie temperature has been explained by the A-B exchange interaction strength due to the change of Fe3+ distribution between A- and B-sites for all the samples. DC electrical resistivity measurements were carried out by two-probe method from 370 K to 580 K. Temperature dependent DC electrical resistivity decreases with increase in temperature ensuring the semiconductor nature of the samples. DC electrical resistivity results are discussed in terms of cations distribution between tetrahedral (A) and octahedral (B) sites. Activation energy calculated from the DC electrical resistivity versus temperature for all the samples. The drift mobility increases by increasing temperature due to decrease in DC electrical resistivity in all the samples. The dielectric constants, dielectric loss and tangent loss factors as a function of frequency for all the samples have been studied as a function of frequency in the range 500 Hz to 1 MHz at room temperature. The dielectric properties have been explained on the basis of space charge polarization resulting from electron displacement which is a major contributor to the dielectric constant in ferrites