We report a comprehensive investigation of the structural, morphological, and magnetic properties of cobalt ferrite (CF) nanoparticles synthesized via a hydrothermal method. X-ray diffraction analysis (XRD), supported by Rietveld refinement, confirmed the formation of a single-phase cubic spinel structure with a lattice parameter of \(8.3621\ {\text{\AA }}\) and an average crystallite size of 12.3 nm. Transmission electron microscopy (TEM) revealed spherical nanoparticles with sizes ranging from 10 to 40 nm. Magnetic measurements indicated a coexistence of ferrimagnetic (FM) and superparamagnetic (SPM) phases at room temperature, with phase fractions of 92% FM and 8% SPM. By separating the SPM component and fitting its magnetization data with a log-normal distribution of Langevin functions, we extracted the magnetic moment distribution, \(f(\mu )\) , and converted it into a particle size distribution, f(D). The analysis yielded a critical size of 13.1 nm, which corresponds to the upper size limit of nanoparticles that can be considered superparamagnetic. These findings highlight the influence of particle size distribution on the magnetic properties of CF nanoparticles, offering valuable insights for their optimization in biomedical and magnetic storage applications.
