Influence of cobalt substitution in CoFe$_2$O$_4$ nanoparticles on structural, morphological, cation distribution, optical and magnetic properties

This paper presents the first-time synthesis of CoFe$_{2-x}$Co$_x$O$_4$ nanoparticles (where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) through hydrothermal methods utilizing metal chloride precursors. X-ray diffraction (XRD) analysis confirms the formation of a cubic spinel structure characterized by the Fdm space group. Field Emission Scanning Electron Microscopy (FE-SEM) images reveal that the average grain size of the nanoparticles lies between 50 nm and 90 nm. Notably, the optical band gap of the Co$^{3+}$-doped samples exhibits a gradual increase from 1.7 eV to 2.5 eV. Furthermore, a reduction in saturation magnetization was noted with increasing doping content at both 5 K and 300 K. The observed decrease in saturation magnetization in the doped samples can be attributed to the migration of Co$^{2+}$ ions from the B site to the A site, as well as the substitution of Fe$^{3+}$ ions with Co$^{3+}$ ions in the B site. Additionally, the influence of annealing temperature on the structure, morphology, and magnetic properties of the nanoparticles was examined.