Effect of doping different rare earth ions on microstructural, optical, and magnetic properties of nickel–cobalt ferrite nanoparticles

Abstract

The influence of doping different rare earth ions (Gd³⁺, Sm³⁺, and Eu³⁺) on the structural, optical, and magnetic properties of Ni–Co spinel ferrite nanoparticles synthesized via chemical co-precipitation method was investigated. The formation of pure cubic spinel phase along with complete solubility of large-sized rare earth ions inside the crystal structure was verified by the X-ray diffractograms. A slight reduction in crystallite size due to hindered crystal growth by the large-sized rare earth ions was also observed. The mean particle size estimated from HRTEM micrograph also followed the X-ray diffraction results closely. The paramagnetic nature of rare earth ions at room temperature also weakens the superexchange interactions between sub-lattices. The coercivity, saturation magnetization, and Curie temperature were observed to reduce in comparison to the pristine sample values due to rare earth ion substitution. The enhancement in indirect allowed optical band gap for all the nanoferrites from the bulk value is attributed to the nanosize effect of the prepared particles.