Impact of In3+ ion substitution on microstructural, magnetic and dielectric responses of nickel–cobalt spinel ferrite nanocrystals

Abstract

In this article, indium ion-doped mixed nickel–cobalt ferrite nanoparticles with chemical composition Ni0.7Co0.3InxFe2−xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.30) were synthesized using soft co-precipitation method. All prepared nanoferrites showed pure cubic spinel structure without containing any impurity phases as ensured by X-ray diffraction profiles. Mean diameters of nanocrystals were found within the range of 5 nm to 13 nm as estimated from Williamson–Hall (W–H) plots. Due to large size of In3+ ions, the compressive microstrain inside the nanocrystals became tensile in nature. Both the coercive field and saturation magnetization were reduced with increasing In3+ ion concentration in nickel–cobalt ferrite nanoparticles. Overall effective anisotropy was noticed to decrease with In3+ ion doping. This is due to the diamagnetic response of indium ions and weakening of magnetic interactions. Hopping of electrons between sublattice sites was the charge conduction process for all nanoferrites as confirmed by the AC conductivity measurement. Single semi-circular arc was observed in Cole–Cole plot for all samples which also revealed that the non-conductive grain boundaries was most effective in comparison to grains in dielectric responses. Decrement in the radius of semi-circles with respect to pristine sample also indicated the enhancement in DC conductivity with indium doping.