Modified Solution Combustion Synthesis of Nickel-Doped Magnetite Nanoparticles and the Influence of Annealing on Their Optical, Electrical, and Magnetic Properties

In this work, nickel-doped magnetite nanoparticles (NPs) are synthesized by a modified solution combustion method and subsequently annealed at different temperatures. We report the structural, optical, dielectric, electrical, and magnetic properties of nickel-doped magnetite nanoparticles (NPs) annealed at 800°C, 1000°C, and 1200°C for 180 min. X-ray diffraction is utilized to explore the structural properties of the prepared magnetic nanoparticles. The surface morphology indicates that the particles annealed at 800°C and 1000°C are spherical, while particles annealed at 1200°C are polyhedral in shape and have uniform distribution. Energy-dispersive spectroscopy reveals the presence of the elements Ni, Fe, and O in the synthesized nanoparticles. The optical spectra obtained from UV–visible spectroscopy reveal that heat-treated synthesized samples have allowed a direct energy band gap. Also, the optical band gap shows a decreasing trend from 1.736 eV to 1.679 eV, while Urbach energy shows an increasing trend from 0.279 eV to 0.539 eV, with increasing annealing temperature. Photoluminescence spectra show a small redshift in band-edge emission from 433.77 nm to 440.12 nm with an increase in annealing temperature from 800°C to 1200°C. The dielectric studies are carried out at (1) varying frequency (20 Hz–2 MHz) at room temperature and (2) varying temperature (100–400 K) at constant frequency of 100 kHz. Both temperature- and frequency-dependent dielectric studies show an increase in the dielectric constant and dielectric loss with an increase in annealing temperature. Also, the conductivity increases with increased temperature in all studied samples, indicating semiconducting behavior, and increased conductivity is observed with increased annealing temperature. The conductivity behavior follows Mott's law, confirming the variable-range hopping mechanism in all samples. Magnetic measurements show high coercivity of 199.12 Oe and high remanent magnetization of 27.35 emu/g at lower annealing temperature. Thus, the magnetic properties of the synthesized ferrite nanoparticles can be tuned by adjusting particle size through annealing temperature.