A comprehensive study on crystal structure, magnetic, and electrical properties of Ni-doped Fe–Cd spinel nano-ferrites

The flash auto-combustion method was used to synthesize nanocrystalline spinel ferrites with the general formula Cd 1− x Ni x Fe 2 O 4 ( x = 0, 0.25, 0.50, 0.75, and 1.0). Structural characterizations of all prepared samples were carried out by the X-ray diffraction technique (XRD), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Broadband dielectric spectroscopy (BDS) and vibration sample magnetometer (VSM) measurements were used to evaluate the dielectric and magnetic characteristics of the synthesized ferrite samples, respectively. The formation of the main cubic phase with space group Fd3m was confirmed by X-ray diffraction examination besides hemitate hexagonal phase α-Fe 2 O 3 . Rietweld refinement revealed that increasing Ni-doping content led to decrease the volume fraction of hemitate hexagonal phase until it vanished at x = 1 and decreasing of lattice parameters. Along with the X-ray diffraction revealed that the particle size and lattice strain were increased with increasing Ni content ( x ). The two distinctive absorption bands of spinel ferrites were identified using FTIR, and their dependency on Ni concentration was studied and explained. The saturation magnetization ( M s ) and coercivity ( H c ) increased as the Ni concentration increased, according to VSM measurements. The frequency dependence of the permittivity for the studied composition as sintered @ 950 °C in comparison with the as-prepared ones shows development of a net of micro-capacitors like behavior in the former. This is due to a thin layer of weakly conducting grain boundaries separating the effectively conducting grains. The conductivity spectra of the compositions show two distinguished trends separated by a characteristic frequency. These three phenomena will be discussed and explained in some detail.