A promising class of ferrimagnetic materials, nickel ferrite (NiFe₂O₄) nanoparticles have great potential for use in microwave devices, magnetic storage systems, catalysis, and biomedical applications such as targeted drug administration. This study offers a thorough analysis of NiFe₂O₄ nanoparticles produced by co-precipitation, including a thorough assessment of both as-prepared and thermally treated (600 °C) samples. Under regulated conditions (pH 10.13 ± 0.06, reaction temperature of 80 °C), the synthesis used a stoichiometric Ni²⁺:Fe³⁺ molar ratio of 1:2. An inverse spinel cubic structure with crystallite diameters of 6.50 nm (as-prepared) and 7.14 nm (calcined at 600 °C), indicating a 9.8% increase after thermal treatment, was validated by structural characterisation using powder X-ray diffraction. Because of particle sintering and agglomeration, calcination increased crystallinity from 70.0% to 73.9% while decreasing specific surface area by 10.3% (from 174 to 156 m²/g). A limited, concentrated size distribution (mean 9.0 nm, 70% within the 7-11 nm range) was shown by scanning electron microscopy study of 200 nanoparticles, indicating good nucleation and growth control. Following calcination, optical characterisation using diffuse reflectance spectroscopy showed a notable 20% decrease in Urbach energy (0.30 to 0.24 eV) and a 3.4% rise in band gap energy (1.76 to 1.82 eV), indicating significantly reduced electronic disorder and enhanced crystalline quality. The XRD crystallite size (6.5-7.14 nm) was significantly smaller than the SEM particle diameter (9.0 nm), indicating that the particles are aggregates of mesoporous primary crystallites. The co-precipitation protocols dependability and scalability were confirmed by a thorough batch-to-batch reproducibility analysis that showed remarkable consistency in product output (82.27 ± 0.83%, coefficient of variation = 1.0%). These results demonstrate the effectiveness and reproducibility of co-precipitation in the production of high-quality NiFe₂O₄ nanoparticles with tunable characteristics, offering quantitative direction for thermal parameter optimization for particular applications.

Keywords: Nickel Ferrite; Thermal Calcination; Urbach Energy; Spinel Ferrites;