Magnetic and Mössbauer spectroscopy studies of NiAl0.2Fe1.8O4/SiO2 nanocomposites synthesized by sol–gel method

•The grain size 5–37 nm of NiAl0.2Fe1.8O4 in NiAl0.2Fe1.8O4/SiO2 nanocomposites were prepared.•The thickness of magnetically dead layer on the surface of ferrite grain was calculated.•The amount of Fe3+ on the surface of grains decreased with increasing annealing temperature.

The structural and magnetic properties of NiAl0.2Fe1.8O4/SiO2 nanocomposites prepared with the sol–gel method were studied by using X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer, and Mössbauer spectroscopy. The average grain size of NiAl0.2Fe1.8O4 in the nanocomposites was found to increase from 5 to 37 nm with increasing the annealing temperature from 800 to 1200 °C while the lattice constant was almost kept a constant of ~0.833 nm. The saturation magnetization of the nanocomposites was shown to increase with increasing the grain size. The thickness of the dead layer on the surface of the ferrite grain was obtained to about (0.61±0.02) nm. The Mössbauer spectra indicated the evolution of magnetic properties of NiAl0.2Fe1.8O4 nanoparticles in the nanocomposites from superparamagnetic to magnetically ordered character with increasing the size of nanoparticles.