Characterization of the dispersion process for NiFe2O4 nanocrystals in a silica matrix with infrared spectroscopy and electron paramagnetic resonance

The structural development of the NiFe2O4 nanocrystals dispersed in a silic a matrix was followed by IR and EPR spectroscopies of the dried gel 10NiO-1 0Fe(2)O(3)-90SiO(2) after heat treatment. The dried gel obtained at 200 deg reesC was amorphous, in which Fe3+ and Ni2+ ions were distributed in the po res of silica matrix. When the dried gel was heat treated at 400 degreesC, NiFe2O4 clusters were partially formed, showing an enhanced interaction wit h the silica matrix. NiFe2O4 clusters were completely formed in silica matr ix when the heat treatment was increased to 600 degreesC, at which the inte ractions between the clusters and silica matrix reached a maximum. The form ation reaction of NiFe2O4 clusters was accompanied by a rearrangement of th e silica matrix network. Further increase of the heat treatment temperature to 800 degreesC led to superparamagnetic single domain NiFe2O4 nanocrystal s (ca. 4 nm) dispersed in the silica matrix with the elimination of the int eractions between magnetic nanocrystals and silica matrix. (C) 2001 Elsevie r Science B.V. All rights reserved.