The structural, magnetic, and optical properties of flame spray pyrolysis‐derived spinel NiFe ₂ O ₄ nanoparticles

Abstract In this study, spinel NiFe 2 O 4 nanoparticles were synthesized employing a one‐step flame spray pyrolysis technique and subjected to annealing at 500°C for 4 h. Thermal, structural, elemental, morphological, magnetic, and photoluminescence properties of the nanoparticles before and after annealing were evaluated using thermogravimetry–differential thermal analyzer, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy, scanning electron microscopy, dynamic light scattering, vibrating sample magnetometry, and fluorescence spectrometer, respectively. Results revealed a pronounced increase in particle size from an average of 80 nm to approximately 140 nm postannealing. XRD verified the retention of the cubic spinel structure with enhanced crystallinity and grain enlargement post‐thermal treatment, without the emergence of additional phases. The photoluminescence analysis showed distinct blue and green emission bands, with excitation at about 364 nm leading to blue emission at 500 nm and green emission at 550 nm both as‐prepared and postannealing. Additionally, magnetic characterization revealed an improvement in saturation magnetization from 16.31 emu/g for the as‐prepared samples to 29.68 emu/g postannealing, underscoring the annealing process's positive impact on magnetic properties. These findings emphasize the potential of tailored NiFe 2 O 4 nanoparticles for applications in magnetic data storage, targeted drug delivery, and bioimaging, driven by modifications in their magnetic and photoluminescence characteristics through thermal treatment.