Sol-Gel Synthesis, Structure, Morphology and Magnetic Properties of Ni 0.6 Mn 0.4 Fe 2 O 4 Nanoparticles Embedded in SiO 2 Matrix.

The structure, morphology and magnetic properties of (Ni 0.6 Mn 0.4 Fe 2 O 4 ) α (SiO 2 ) 100-α (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 0.6 Mn 0.4 Fe 2 O 4 , while at high calcination temperatures, well-crystallized Ni 0.6 Mn 0.4 Fe 2 O 4 was obtained along with α-Fe 2 O 3 , quartz, cristobalite or iron silicate secondary phase, depending on the Ni 0.6 Mn 0.4 Fe 2 O 4 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 2 matrix. The saturation magnetization ( Ms ) enhances from 2.5 to 80.5 emu/g, the remanent magnetization ( M R ) from 0.68 to 12.6 emu/g and the coercive field ( H C ) from 126 to 260 Oe with increasing of Ni 0.6 Mn 0.4 Fe 2 O 4 content in the NCs. The SiO 2 matrix has a diamagnetic behavior with a minor ferromagnetic fraction, Ni 0.6 Mn 0.4 Fe 2 O 4 embedded in SiO 2 matrix displays superparamagnetic behavior, while unembedded Ni 0.6 Mn 0.4 Fe 2 O 4 has a high-quality ferromagnetic behavior.