Local structure of directly synthesized [L1.sub.0] FePt nanoparticles

The FePt particles synthesized by polyoi process using tetraethylene glycol (TEG) as reducing agent at reaction temperatures 200 [degrees]C and 300 [degrees]C are superparamagnetic and ferromagnetic, respectively. The crystal structure of these particles is analyzed using XRD, XAS, and ASAXS to understand the formation of these particles at different heating temperatures. The results suggest that at 200 [degrees]C particles with Pt rich FePt core and amorphous shell rich in Fe are formed. However, when the reaction solution is annealed at 300 [degrees]C, sintering of several small particles occur. On the other hand, when hexachloroplatinum as nucleation control agent and a carboxylic acid as complex agent was added into the reaction solution, homogeneous alloy FePt particles with relatively large grain size of about 8 nm were obtained. In the process of forming the alloy nanoparticles, precipitated small particles were sintered at the amorphous interface and crystallization progresses along with ordering resulting in the formation of partially ordered ferromagnetic FePt. Index Terms--ASAXS, fcc-FePt, fct-FePt, polyol process, XAFS.