Structure and magnetic properties of Co nanoclusters fabricated by ion beam synthesis in SiO2 films.

Abstract: Co nanoparticles fabricated by ion beam synthesis in SiO2 films were inve-stigated with TEM and SQUID technique. The variation of the thermal treatment enables the formation of Co nanoclusters of different sizes ranging from 2 to 40 nm. Small nanoclusters of about 2-3 nm are amorphous, whereas clusters above 7 nm show the configuration of cubic Co nanocrystals. Measurements of magnetization at tem-peratures between 2 K and 360 K reveal superparamagnetic behaviour for the small nanoclusters up to 3 nm and ferromagnetism for clusters above 7 nm .