Superparamagnetism and coercivity in HCP-Co nanoparticles dispersed in silica matrix

The magnetic properties of Co HCP nanoparticles dispersed in a silica matrix with sizes between 270: 7 and 5 +/- 2.2 nm were investigated. The temperature dependence of zero-field cooled and field cooled magnetizations and of the coercive field were analyzed considering the thermal activated demagnetization process. Enhanced anisotropy was observed for the 2 nm nanoparticles, while the demagnetization process of the larger ones is dominated by interparticle interactions.