This report describes the physical characterization of cobalt nanoparticles formed using (1) polysiloxane copolymer micelles and (2) poly(styrene-b-4-vinylphenoxyphtalonitrile) copolymer solutions. Formation of silica coatings around the cobalt nanoparticles is shown to protect the cobalt from oxidation in aerobic environments. Native particles have a narrow particle size distribution while pyrolyzed particles appear to comprise a bimodal or broader distribution of sizes. Pyrolysis of the native sample increases the cobalt specific saturation magnetization. Native cobalt nanoparticles formed in poly(styrene-b-4-vinylphenoxyphthalonitrile) copolymer solutions are weakly crystalline while their pyrolyzed counterparts have a high degree of crystallinity. Pyrolysis increases the cobalt specific saturation magnetization from approximately 80 emu/g Co to values close to that observed for bulk cobalt (160 emu/g Co). The formation of a graphitic coating around the cobalt nanoparticles upon pyrolysis appears to prevent oxidation of the cobalt in air.
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