Effect on structural and magnetic properties of aluminum substituted Ni-Zn nanoferrite system prepared via citrate-gel route

Nickel zinc aluminum nanoferrites with general formula Ni0.5Zn0.5Fe2-xAlxO4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) were prepared by citrate-gel autocombustion method and heat treated in air at 1100 degrees C for 4 h. The crystallography, surface morphology and magnetic properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure and absence of any secondary phases. The crystallite size estimated from Scherrer formula for the Gaussian peak (311) has been found to be around 30 nm. The results obtained show that with Al3+ doping, the lattice parameter decreases due to smaller ionic radii of Al3+ ions replaces larger Fe3+ ions. The distribution of Al3+ ions over tetrahedral (A) and octahedral (B) sites is estimated from X-ray intensity calculations. The arrangement of magnetic ions among the tetrahedral and octahedral sites due to the substitution of Al3+ ions modifies the saturation magnetization (M-s) and coercivity (H-c). The room temperature magnetization values increases up to x = 0.1 and then decreases for the increase in aluminum concentration above x > 0.1. Surface topography of the powder samples exhibits nearly spherical shape microstructure and the average grain size has been found to be 180 nm (x = 0.05). The observed variations in the structural and magnetic properties are discussed in the light of existing understanding.