Effect of Additive Cu, Ag, and Au on L1_0 Ordering in Chemically Synthesized FePt Nanoparticles

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FePtCu, FePtAg, and FePtAu nanoparticles have been chemically synthesized using a modification of the method reported by IBM for synthesizing FePt nanoparticles. The procedure involved the simultaneous polyol reduction of platinum acetylacetate and the appropriate metal additive reagent and the decomposition of iron pentacarbonyl in the presence of organic surfactants. The ternary particles possess the disordered fee structure and are approximately 4 nm in diameter with uniform particle size, which is approximately the same as for FePt without the additive metals. The effect of the additive metal on the transformation to the L1_0 phase has been studied. Cu increases the temperature required for phase transformation and leads to mixed phases at high annealing temperature, while Ag and Au lower the temperature for transformation by 100-150℃. During heat treatment Cu remains in the particles while Ag and Au segregate. The anisotropy of (FePt)_<76>Au_<24> annealed at 500℃ for 30 min is approximately 3×10^7 erg/cc. Measurements of the X-ray diffraction line width and magnetic switching volume suggest that the nanoparticles sinter during the phase transformation.
社団法人日本磁気学会の論文
2004-07-01