SIZE QUANTIZATION AND INTERFACIAL EFFECTS ON A NOVEL GAMMA-FE2O3 SIO2MAGNETIC NANOCOMPOSITE VIA SOL-GEL MATRIX-MEDIATED SYNTHESIS/

Novel isolated magnetic single-domain gamma-Fe2O3 nanoclusters have be en prepared by coprecipitation of ferrous and ferric salts encapsulate d within sol-gel derived silica (SiO2). The nonmagnetic SiO2 coating f ormed by hydrolysis and polycondensation of tetraethoxysilane on the s urface of the Fe2O3 nanoclusters provides a means for thermally stable dispersion of Fe2O3 clusters. The precipitated particles coated with SiO2 are spherical with 4-5 nm diameters. Surface and strain effects p layed a critical role in determining the overall magnetic behavior of the spherical single-domain particles. Superparamagnetic behavior was observed by superconducting quantum interference device magnetometry a nd Mossbauer spectroscopy. Superparamagnetic barrier energies and the low-temperature coercivities were modified through cluster/support int erface microstructure manipulation. The optical studies showed the abs orption edge of the nanocomposites to be slightly blue shifted in the UV-VIS spectrum range when compared to that of bulk gamma-Fe2O3. This was attributed to the combined effects of the quantum confinement of t he nanocrystalline gamma-Fe2O3 clusters and the stress present at the particle/support interface. The magnetic properties can be manipulated via the matrix microstructure, synthesis conditions and thermal treat ment. (C) 1997 American Institute of Physics.