Magnetic nanostructures in a glass ceramic characterized by small angle neutron scattering

Nanocrystalline magnetite Fe3O4 embedded in a non-magnetic matrix was forme d by heat treatment of Cn-Si-B-Fe-oxide glass. Small Angle Neutron Scatteri ng (SANS) revealed a bimodal volume size distribution for the nanocrystalli ne phase with maxima centred at radii of 2.5 nm and 10 nm, respectively. Th e magnetic scattering behaviour is characteristic for superparamagnetism of single-domain particles following the Langevin statistics. Both fractions of nanocrystals are composed by a superparamagnetic core surrounded by a no nmagnetic surface layer. Magnetisation measurements indicate different ther mal variation of the superparamagnetic moments ill both fractions of nanocr ystals. (C) 1999 Acta Metallurgica Inc.