Magnetic and structural investigation of highly porous CoFe ₂O₄-SiO₂ nanocomposite aerogels

The structural and magnetic properties of CoFe₂O ₄-SiO₂ nanocomposite porous aerogels have been systematically investigated by XRD, TEM, and SQUID magnetometry. The preparation of the samples was performed by a cogelation sol-gel route which allows one to obtain nanocomposites with high purity and homogeneity and to control the composition of the sample in terms of ferrite loading in the nanocomposite. In particular, the compositional effect on both the structural and magnetic properties of the nanocomposite was investigated in two nanocomposites with relative CoFe₂O₄ amounts of 5 and 10 wt %. The characterization shows both similarities and differences in the structural evolution of the nanophases within the amorphous porous matrix of the two nanocomposites as a function of the calcination temperature. In both samples the ferrite nanoparticles are formed above 750 °C; however, a slower structural evolution is observed in the nanocomposites with 5 wt % CoFe₂O ₄. The nanocomposites display superparamagnetic behavior with blocking temperature that increases with both the ferrite amount and the calcination temperature. The importance of combining information from different techniques is also discussed, with particular reference to nanocrystal size determination. The results provide insights into the characterization of innovative materials and on how the compositional and microstructural features affect the properties of magnetic nanocomposites.