title: Characterization of superparamagnetic "core-shell" nanoparticles and monitoring their anisotropic phase transition to ferromagnetic "solid solution" nanoalloys.
abstract: The structure, magnetism, and phase transition of core-shell type CoPt nanoparticles en route to solid solution alloy nanostructures are systematically investigated. The characterization of Co(core)Pt(shell) nanoparticles obtained by a "redox transmetalation" process by transmission electron microscopy (TEM) and, in particular, X-ray absorption spectroscopy (XAS) provides clear evidence for the existence of a core-shell type bimetallic interfacial structure. Nanoscale phase transitions of the Co(core)Pt(shell) structures toward c-axis compressed face-centered tetragonal (fct) solid solution alloy CoPt nanoparticles are monitored at various stages of a thermally induced annealing process and the obtained fct nanoalloys show a large enhancement of their magnetic properties with ferromagnetism. The relationship between the nanostructures and their magnetic properties is in part elucidated through the use of XAS as a critical analytical tool.
authors.affiliation: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
authors.forename: Jong-Il
authors.initials: JI
authors.lastname: Park
authors.forename: Min Gyu
authors.initials: MG
authors.lastname: Kim
authors.forename: Young-Wook
authors.initials: YW
authors.lastname: Jun
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Lee
authors.forename: Woo-Ram
authors.initials: WR
authors.lastname: Lee
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Cheon