Effect of Magnesium Substitution on Structural and Magnetic Properties of Nickel Ferrite Nanoparticles

Magnesium-substituted Ni-ferrite (Mg_xNi_{1 − x}Fe₂O₄; 0 ≤ x ≤ 1) nanoparticles were prepared by sol-gel method and were annealed at 550 °C and 900 °C in air. All the as-prepared samples and the samples annealed at 550 °C were single phase whereas some additional peaks of α-Fe₂O₃ was observed for the samples annealed at 900 °C. Lattice constant increased with the increase in Mg²⁺ concentration. Crystallite size did not show any systematic variation with the increase in Mg²⁺ concentration and was increased after annealing in these nanoparticle samples. The highest M_S values of 42 and 46 emu/g were observed at 300 and 60 K respectively for the as-prepared sample with x = 0.05 and the lowest values of 21 and 26 emu/g were observed at 300 and 60 K respectively for the 550 °C-annealed sample with x = 1. The magnetization and coercivity decreased with the increase in Mg²⁺ concentration. The non-saturation behavior was found to be increased with the increase in Mg²⁺ concentration in these samples. The observed magnetic behavior can be understood on the basis of increase in nonmagnetic Mg²⁺ concentration, cation distribution in the lattice sites, growth of crystallite size, and the decrease in anisotropy with the increase in Mg²⁺ concentration in these nanoparticle samples.