Semi-hard magnetic properties of nanoparticles of cobalt ferrite synthesized by the co-precipitation process

Abstract The nanoparticles ferromagnetic materials CoFe 2 O 4 have been synthesized by the co-precipitation method and annealed at various temperatures from 773 to 1223 K. The influence of the heat treatment on the structural, morphological and magnetic properties of CoFe 2 O 4 nanoparticles was investigated. The structure, morphology and magnetic properties of the annealing samples were reached by mean of X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques and measurement of hysteresis loop. The average crystallite size, lattice parameter and X-ray density were calculated from X-ray diffraction data. All samples have the cubic spinel structure with average crystallite sizes increasing from 30 to 178 nm with the temperature. The results show that CoFe 2 O 4 nanoparticles prepared by this method have small and more uniform size. The measurements of the hysteresis loop, performed at both 10 K and 300 K, indicate a ferromagnetic behavior of nanoparticles. Also the measurement at 300 K shows that the sample annealed at 1023 K is magnetically harder than the other samples. The coercive fields are 1.58 kOe against the values inferior at 0.61 kOe for the other samples. Indeed, the remanent magnetization is 31.85 emu g −1 for the hard magnetic sample against 13.02 and 17.29 emu g −1 for the soft magnetic samples annealed at 773 and 1223 K, respectively. The origin of the hard-soft magnetic properties of nanoparticles CoFe 2 O 4 is discussed in terms of the co-existence of secondary phases β -Fe 2 O 3 , CoO 2 and the distribution of Fe 2 + and Co 2 + ions within the lattice.