Characterization of superparamagnetic "core-shell" nanoparticles and monitoring their anisotropic phase transition to ferromagnetic "solid solution" nanoalloys.
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.
Park
Jong-Il
JI
Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
Kim
Min Gyu
MG
Jun
Young-Wook
YW
Lee
Jae Sung
JS
Lee
Woo-Ram
WR
Cheon
Jinwoo
J