| Summary: | The structure, morphology and magnetic properties of (Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub>)<sub>α</sub>(SiO<sub>2</sub>)<sub>100−α</sub> (α = 0–100%) nanocomposites (NCs) produced by sol-gel synthesis were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and vibrating sample magnetometry (VSM). At low calcination temperatures (300 °C), poorly crystallized Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub>, while at high calcination temperatures, well-crystallized Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub> was obtained along with α-Fe<sub>2</sub>O<sub>3</sub>, quartz, cristobalite or iron silicate secondary phase, depending on the Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub> content in the NCs. The average crystallite size increases from 2.6 to 74.5 nm with the increase of calcination temperature and ferrite content embedded in the SiO<sub>2</sub> matrix. The saturation magnetization (<i>Ms</i>) enhances from 2.5 to 80.5 emu/g, the remanent magnetization (<i>M<sub>R</sub></i>) from 0.68 to 12.6 emu/g and the coercive field (<i>H<sub>C</sub>)</i> from 126 to 260 Oe with increasing of Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub> content in the NCs. The SiO<sub>2</sub> matrix has a diamagnetic behavior with a minor ferromagnetic fraction, Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub> embedded in SiO<sub>2</sub> matrix displays superparamagnetic behavior, while unembedded Ni<sub>0.6</sub>Mn<sub>0.4</sub>Fe<sub>2</sub>O<sub>4</sub> has a high-quality ferromagnetic behavior.
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