Investigation of nickel effects on some physical properties of magnesium based ferrite

Mg0.6−xNixCo0.4Fe2O4 (x = 0 and x = 0.2) ferrites are elaborated under same conditions using the Pechini sol-gel technique. The obtained samples reveal a single phase without any detectable of secondary phase. But, the introduction of nickel in the parent ferrite system affects the grains shape, lattice parameters, volumetric mass density and the electrical resistivity. The X-ray diffraction patterns indicate that the investigated ferrites reveal a single phase without any detectable of secondary phase. Also, grains in the nickel doped compound have prismatic shape which indicates a better crystallization than in undoped one. From electrical measurements, a dramatically decrease of resistivity is observed at low temperature range. A decrease with 7 decades is observed in the temperature range 100 K-500 K. Both samples exhibit a semiconductor character in an important temperature range 80 K-700 K. The nickel effect on the electrical resistivity is well pronounced at higher temperature region (T > 150 K). Also, the nichel addition reduces the activation energy. Such variation is associated to the chemical composition, cristallite size, porosity, grain boundary and density effects. In a specific temperature range (ΔT), the ac-conductivity of the investigated materials becomes almost frequency independent. For x = 0 and x = 0.2, such range increases from ΔT = 100 K to ΔT = 220 K respectively. For x = 0.2 and for f ≤ 160 kHz, such range is extended from ambient temperature to 700 K to be ΔT = 400 K. This behaviour may be important to make the material suitable for some desired applications. Impedance analysis confirms the contribution of grain boundary on transport properties and proves the presence of relaxation phenomenon in nickel-magnesium ferrite. The temperature dependence of the average normalised change parameter is in good agreement with the temperature dependence of the dc-resistivity and the ac-conductivity of the investigated samples.