Synthesis and characterisation of silica encapsulated cobalt nanoparticles and nanoparticle chains

Nanoparticles of cobalt were produced by direct reduction in aqueous solution. These were subsequently coated in silica by a very slow hydrolysis reaction. Electrostatic and magnetic forces between the nanoparticles led to ordered structures forming, which were analysed by high resolution transmission electron microscopy. SQUID magnetometry showed that the nanoparticles were ferromagnetic with an additional magnetic signal from highly disordered surface states. Off-axis electron holography of the structures was undertaken and gives evidence for the mechanism by which the structures form.