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 (4)A(2) -> T-4(1) (F-4) transition while the former is attributed to the overlapping of the (4)A(2) -> T-4(1) (F-4) 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 (CoFeO4)-O-2 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. (C) 2010 Elsevier B.V. All rights reserved.