Structural, magnetic and electrical properties of cobalt ferrites prepared by the sol–gel route

Abstract

Abstract Nanosized cobalt ferrites having the general formula CoFe 2− x Al x O 4 (for x = 0.00, 0.25, 0.50) have been synthesized by the sol–gel route. The effect of Al 3+ ions on structural, Curie temperature, DC electrical resistivity and dielecltric properties are presented in this paper. From the analysis of powder X-ray diffraction patterns, the nanocrystallite size was calculated by the most intense peak (3 1 1) using Scherrer formula. The crystallite size decreases with increase in aluminium concentartion. The lattice parameter ‘ a ’ also decreased with increase in aluminum concentration. The magnetic and electrical properties have been studied as a function of temperature. The Curie temperature was determined from AC magnetic susceptibility measurement. It is observed that Curie temperature decreases and DC electrical resistivity increases with increasing concentration of Al 3+ ions. The observed variations in DC electrical resistivity have been explained by Verwey's hopping mechanism. The activation energy was found to increase with increasing Al 3+ ions. The variations of dielectric constant for all the samples have been studied as a function of frequency in the range 500 Hz to 1 MHz at room temperature. The room temperature dielectric constant decreases with increase of trivalent Al 3+ ions. The observed variation in dielectric constant has been explained on the basis of space charge polarization.