The impact of cobalt insertion on the structural and magnetic properties of nonstoichiometric ZnCo<inf>x</inf>Fe<inf>1.7</inf>O<inf>4</inf> (x >0.3) nanoferrites

Abstract

A single-phase nanoferrite ZnCoxFe1.7O4 (0.37≤ x ≤0.9) system has been prepared via the citrate autocombustion method. Nonstoichiometry has been progressively enhanced in the synthesized samples by increasing the cobalt content. Both XRD patterns and IR spectra have confirmed a pure cubic phase for all as-prepared samples and for that with × = 0.9 sintered at 700°C. Interestingly, the lattice parameter showed a general decreasing trend with increasing x. The determined crystallite size of as-prepared samples ranged from 17 to 30 nm in agreement with the HRTEM images. For as-prepared samples, the M−H loops exhibited nearly superparamagnetic behavior, while antiferromagnetic behavior was observed for the sintered sample. According to the suggested cation distribution, continuous insertion of Co2+ in the formula unit is compensated by both the reduction of Fe3+ cations to Fe2+ ones and the progressive occupation of Zn2+ in the 16c positions.