Magnetic properties of Ni ferrite nanocrystals dispersed in the silica matrix by sol-gel technique

NiFe2O4/SiO2 nanocomposites have been prepared by the sol gel technique using tetraethylorthosilicate (TEOS) as precursor of the silica matrix, metallic nitrates as precursors of ferrites and formamide as a modifier. After heat treatment, the various samples have been studied by means of X-ray diffraction, IR and magnetic measurements. X-ray diffraction and IR spectra confirmed the presence of the spinel phase. Scherrer revealed the nanocrystals with the mean size in the range of 15 nm. Magnetic properties depending on the calcining temperature and the concentration of Ni ferrite are discussed. These results showed an analogous superparamagnetic behavior for the samples heated at lower temperature and ferrimagnetic character for the samples heated at higher temperature. The magnetization of nanocomposites almost linearly varied with the content of Ni ferrite. (C) 2004 Elsevier B.V. All rights reserved.