Investigations on microstructure, electrical and magnetic properties of Ni-Zn-Ga spinel ferrites

Two spinel ferrite samples Ni0.7Zn0.3GayFe2-yO4 (y = 0.5, 1.0) were prepared by both ceramic and citrate methods. X-ray diffraction patterns indicated a single phase of cubic structure for all the samples that have a space group Fd-3m. Rietveld analysis using MAUD software for all samples showed that the lattice parameter (a) decreases, while oxygen parameter (U) and strain () increase by increasing the amount of Ga. A marked increase in the frequency bands in both the tetrahedral and octahedral sites was observed in the vibrational frequency bands of Fourier transform infrared spectra. Mossbauer effect (ME) spectra recorded at room temperature for the bulk sample (prepared by ceramic method) with lower concentrations of Ga3+ (y = 0.5) consist of two Zeeman sextets. ME spectra for the other bulk sample (y = 1.0) and the two samples in nanoscale (prepared by citrate method) can be fitted by one and two doublets due to the paramagnetic and superparamagnetic behaviour, respectively. Vibrating sample magnetometer measurements showed that the saturation magnetization (M-s) obtained from the hysteresis loop is decreased by increasing Ga3+ concentration for all the samples. The coercivity (H-c) is inversely proportional to the particle size (D) for bulk samples. Nevertheless, H-c of the nanoscale samples enhanced by increasing the particle size. The size dependence of H-c is an indication of the superparamagnetic characteristics supported by ME. The ac electrical conductivity (ln sigma), dielectric constant (epsilon ') and dielectric loss tangent (tan delta) were studied at different frequencies and temperatures for the investigated samples. The obtained results showed that the conductivity for all samples increases with increasing temperature in a behaviour similar to that of the most semi-conductor materials.