Influence of order-disorder effects on the magnetic and optical properties of NiFe 2 O 4 nanoparticles
Abstract In this study, we focused on the influence of structural order-disorder effects on the magnetic and optical properties of single-phase nickel ferrite (NiFe 2 O 4 ) nanoparticles that, were synthesized by the co-precipitation method and subsequently calcined at 700, 800, 900 and 1000 °C for 120 min in ambient atmosphere. These results from X-ray diffraction and transmission electron microscopy confirm that the NiFe 2 O 4 nanoparticles have an inverse spinel structure with high purity and crystallinity. The average particle size range between 12 nm and 42 nm depending on the calcination temperature. An analysis of the hysteresis loops revealed a ferromagnetic behavior with an increase in saturation magnetization to 13.2 emu/g from 8.2 emu/g at room temperature. At 7 K, the nanoparticles exhibited saturation magnetization of about 18.1–19.8 emu/g and change in crystallite size, as the calcination temperature increased. UV–vis diffuse spectra results showed an increase in the direct band gap in the range 1.35–1.43 eV, likely due to the increased crystallinity of the NiFe 2 O 4 nanoparticles. Photoluminescence spectroscopy revealed a strong emission in the visible region, which can easily be attributed to the presence of structural disorders in the [FeO 6 ], [FeO 4 ], and [NiO 6 ] clusters of the NiFe 2 O 4 powders. Finally, it was found that these NiFe 2 O 4 powders as-prepared have oxygen atoms that occupy different positions and are highly disturbed in the NiFe 2 O 4 lattice. These findings provide insights into the magnetic and optical behavior of NiFe 2 O 4 spinel nanocrystals, with a significant emphasis on structural order-disorder effects, and help reveal the relationship between structure and properties at the atomic level.