Hyperfine characterization of the crystallization of nanocrystalline NiFe2O4 from the amorphous silica gel

Nanocrystalline NiFe2O4 was in-situ prepared in amorphous silica using tetr amethylor-thosilicate and nickel (iron) nitrate hydrate as the starting mat erials in a sol-gel reaction. The magnetic nanocrystals in the amorphous si lica glasses grew slowly with increasing temperature. Above 600 degreesC, n ickel ferrite nanoparticles began to precipitate from the amorphous silica matrix. Mossbauer spectroscopy of the nanocomposites suggested that in the silica glasses, Fe ions were present exclusively as Fe3+ in octahedral coor dination, and the chemical environment of the Fe3+ ions appeared to remain unchanged until the crystallization of nickel ferrite nanocrystals. The for mation of NiFe2O4 nanocrystals was the result of partial transformation of the FeO6 octahedra to FeO4 tetrahedra. The nanocrystalline NiFe2O4 are char acterized by super-paramagnetic behaviour at room temperature.