Remarkable structural and magnetic properties of nickel-zinc spinel ferrites synthesized by refluxing method

The structural and magnetic properties of the spinel ferrite system $\text{N}{\text{i}}_{0.36}\text{Z}{\text{n}}_{0.64}\text{F}{\text{e}}_{2+z}{O}_4$ (z = 0.00, 0.05, 0.10) synthesized by the reflux method were thoroughly investigated. X-ray diffraction (XRD) and Raman spectroscopy confirmed the formation of a single-phase cubic spinel structure, with crystallite sizes ranging from 8.20 nm to 11.3 nm. High-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) revealed semi-spherical nanoparticles. Brunauer-Emmet-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses indicated a type IV isotherm, characteristic of mesoporous materials with relatively high surface area. Electron density maps showed enhanced electron density at B-sites and around Zn ions, with moderate displacement of oxygen positions within the unit cell compared to Ni and Fe sites. The vibrating sample magnetometer (VSM) measurements at room temperature revealed superparamagnetic behavior of the nanoparticles, with high saturation magnetization. The coercive field decreased monotonically with increasing excess Fe ions, while remnant magnetization exhibited correlation with saturation magnetization. A strong correlation between saturation magnetization and crystallite size was also observed.