Investigation of the Structural, Elemental, and Magnetic Properties and Intensity-Dependent Third-Order Nonlinearity of Nickel Ferrite for Hyperthermia and Nonlinear Optical Application.

An economical sol–gel auto-combustion method aided by citric acid was used to synthesize nickel ferrite ( NiFe 2 O 4 ) nanoparticles (nickel nitrate/ferric nitrate at 1:2 and metal nitrate with citric acid at 1:1, stirring condition: 600 rpm). The impurity phase present in as-synthesized nickel ferrite was removed by sintering at 950°C in a microwave furnace. Powder x-ray diffraction of the sintered sample confirmed the removal of impurity phase and showed the spinel cubic nature of the particles. The crystallite sizes of both as-synthesized and sintered particles were calculated using the Scherrer and Williamson–Hall formulas, which confirmed the formation of nanoparticles. Further, the particle size distribution and morphology of both samples were calculated using scanning electron microscopy with the help of ImageJ software. The UV–Vis spectroscopy of the particles showed strong absorption between 200 nm and 600 nm. The room-temperature magnetic hysteresis analysis revealed that both the as-synthesized (NFO-As) and sintered (NFO-950) materials exhibited a ferromagnetic nature, with maximum saturation magnetization of 50.84 emu/g for NFO-950 and higher coercivity of 179.76 Oe for NFO-As. Specific absorption rate (SAR) values of 7.976 W/g and 11.54 W/g were determined for NFO-As and NFO-950, respectively, from induction tests, which suggests the material is a suitable candidate for hyperthermia treatment. Additionally, investigation of the particles' third-order nonlinear characteristics using a Ti-sapphire femtosecond laser showed reverse saturation absorption for NFO-950. The average nonlinear absorption coefficient of NFO-950 was found to be 1.44 times that of copper ferrite nanoparticles, rendering it a suitable candidate for optical limiting applications. [ABSTRACT FROM AUTHOR]