Journal
IEEE TRANSACTIONS ON MAGNETICS
Volume 49, Issue 7, Pages 3303-3306Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TMAG.2013.2243710
Keywords
EXAFS; L1(0)-type structure; local structure; polyol process
Funding
- Japan Society for Promotion of Science [23760620]
- Photon Factory Program Advisory Committee [2010G661]
- Grants-in-Aid for Scientific Research [23760620] Funding Source: KAKEN
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The ordering process of FePt nanoparticles synthesized in polyol solution at 383 K was investigated. Whereas X-ray diffraction peaks of the as-synthesized specimen corresponded to the fcc structure, the Fe-O correlation and Pt-O correlation peaks were observed in the radial structure functions of Fe and Pt atoms obtained by X-ray absorption spectroscopy. Thus, the as-synthesized specimen was composed of crystalline FePt alloy phase and poorly crystallized Fe- and Pt-oxide phase. In X-ray diffraction patterns of the specimens which were heat-treated at temperatures above 568 K in a mixture of 5% H in Ar, diffraction peaks corresponding to superlattice lines were observed. Although the lattice constants of the as-synthesized specimen were much larger than that of the bulk fcc-FePt alloy with equiatomic composition, the lattice constants of the specimen heat-treated at 1173 K were very close to the bulk L1(0)-FePt alloy. Additionally, in the radial structure function, peaks corresponding to the Fe-O and Pt-O correlations disappeared and peaks corresponding to Fe-Pt (or Fe) and Pt-Fe (Pt) correlations clearly appeared after heat treatment at temperatures above 568 K. Consequently, it is highly probable that the disorder-order transformation of FePt nanoparticles synthesized in polyol solution is accompanied by compositional homogenization due to the reduction of the poorly crystallized Fe- and Pt-oxide phase.
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