Optical, magnetic and electrical investigation of cobalt ferrite nanoparticles synthesized by co-precipitation route

Aluminum substituted cobalt ferrite nanoparticles CoFe2−xAlxO4 (for x = 0.00, 0.25, 0.50) have been synthesized by the chemical co-precipitation route. The average crystallite size was calculated using the Scherrer formula and found within 17–27 nm range. The optical absorption spectra of all the samples showed two clear electronic transitions, first is around 0.75 eV while the second at about 0.84 eV. The later is identified by means of 4A2 → 4T1 (4F) transition while the former is attributed to the overlapping of the 4A2 → 4T1 (4F) transition of the tetrahedral Co2+ ions and the Co2+ + Fe3+ → Co3+ + Fe2+ metal–metal charge transfer transition. The saturation magnetization at room temperatures was found to be 61.50 emu/g for pure CoFe2O4 nanoparticles, while it decreased with increasing Al3+ concentration up to 52.00 emu/g (for x = 0.50). The Curie temperature was determined from AC magnetic susceptibility measurement. It was observed that Curie temperature decreased with Al3+ concentration (x) and DC electrical resistivity decreased with increase in temperature. Activation energy and drift mobility have been calculated from the temperature dependent DC electrical resistivity measurements for all the samples. The variation of dielectric constant, dielectric loss and tangent loss factor for all the samples have been studied as a function of frequency in the range 600 Hz to 1 MHz at room temperature.

Research highlights▶ Particle size reduces to less than 50 nm. ▶ DC electrical resistivity increases with substitution of Al. ▶ Dielectric constant decreases. ▶ Dielectric loss factor also decreases with substitution of Al. ▶ High dielectric constants decrease the penetration depth of the electromagnetic waves by increasing the skin effect. Hence, the much lower dielectric constants obtained for the ferrites warrant their application at high frequencies.