• Baranauskas, V. V.
• Riffle, J. S.
• Zalich, M. A.
• Pierre, Tim St
• Saunders, Martin

Abstract

Oxidatively stable magnetic cobalt nanoparticles were prepared by annealing cobalt nanoparticles coated with poly(styrene-b-4-vinylphenoxyphthalonitrile) block copolymers. An oxygen-impermeable graphitic coating around the cobalt nanoparticles was created during thermal treatment at 700 degrees C owing to the thermal decomposition/cross-linking of a polymer with a highly aromatic character. A variety of analytical techniques were used to elucidate the physical properties of the pre-heat-treated and heat-treated samples. The cobalt-specific saturation magnetization (sigma(s)) increased from 81 to 173 emu g(-1) Co upon heating of the polymer-coated cobalt nanoparticles. The pre-heat-treated sample readily oxidized, as revealed by low-temperature magnetic susceptometry studies, whereas the heat-treated sample showed oxidative stability for over 1 year. The mean cobalt particle size increased from 18.5 to 36.1 nm during thermal treatment. Electron diffraction and X-ray diffraction revealed that the pre-heat-treated particles were weakly crystalline, while the heat-treated particles were strongly crystalline. The dominant phase of the heat-treated sample was determined to be face-centered cubic with other minor phases present ( hexagonal close packed and epsilon).

Topics

• nanoparticle
• phase
• x-ray diffraction
• Oxygen
• electron diffraction
• cobalt
• annealing
• copolymer
• block copolymer
• magnetization
• thermal decomposition
• saturation magnetization