Direct synthesis and characterizations of fct-structured FePt nanoparticles using poly(N-vinyl-2-pyrrolidone) as a protecting agent.
FePt alloy in a bulk state is well known as a magnetic material. FePt nanoparticles, which are protected by poly(N-vinyl-2-pyrrolidone) (PVP) and have a face-centered tetragonal (fct) structure at a size of a few nanometers in diameter, have been directly synthesized by a polyol process in high-boiling point tetraethylene glycol used as a reducing reagent for the reduction of Fe(III) acetylacetonate and Pt(II) acetylacetonate. Their magnetic properties (coercivity and saturation magnetization) were dependent on the size and made progress as their diameters increased. The size in diameter was easily controlled by altering the content of PVP, the time for refluxing, and reaction temperature. FePt nanoparticles showed diameter-dependent coercivities at room temperature and they abruptly increased at over 4 nm in diameter. Ferromagnetic FePt nanoparticles with an fct structure were also synthesized at relatively low reaction temperature without refluxing. Likewise, as-synthesized FePt nanoparticles prepared by refluxing at 251 degrees C for 3 h displayed the fct structure and clearly indicated the ferromagnetism at room temperature. Reaction kinetics such as long refluxing time and slow temperature elevation rate were found to be important key factors to synthesize the ferromagnetic FePt nanoparticles although the reaction temperature was very critical as well.
Iwamoto
Takashi
T
Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan. iwamoto@ed.yama.tus.ac.jp
Matsumoto
Kinya
K
Matsushita
Toru
T
Inokuchi
Makoto
M
Toshima
Naoki
N