Background: Nowadays, spinel ferrite magnetic nanoparticles have extensive applications in various fields, including medicine, information technology, and energy. Properties such as high Curie temperature, high electrical resistivity, and low eddy current losses make these materials suitable for use in permanent magnets, transformer cores, and targeted drug delivery systems.
Aim: The effect of Ni3+ on the structural and magnetic properties of Ni1+xFe2-xO4 nanoparticles was investigated for x = 0, 0.5, and 1. These samples were also examined at three annealing temperatures: 250°C, 500°C, and 1000°C. Finally, magnetic domains, interparticle interactions, intrinsic properties, and magnetic evolution were analyzed using FORC analysis. Methodology: In this study, Ni1+xFe2-xO4 nanoparticles were synthesized using the sol-gel method. Their magnetic and structural properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FTIR), hysteresis loop analysis, and First-Order Reversal Curve (FORC) analysis. Conclusions: The results of this study demonstrated that annealing temperature significantly affects the crystal structure, magnetic properties, and particle morphology. At lower temperatures (250°C), an amorphous structure with reduced magnetization was observed, whereas at higher temperatures (500°C and 1000°C), the spinel crystalline structure was stabilized. An increase in nickel content resulted in changes in lattice parameters, a reduction in magnetic moment, and variations in magnetic behavior at each temperature. Additionally, the growth of crystallite size and transitions between single-domain and pseudo-single domain behavior were found to be dependent on temperature and chemical composition. FTIR and microscopy analyses further confirmed the spinel structure and morphological