Towards direct synthesis of fct-FePt nanoparticles by chemical route

Abstract

The possibility for direct synthesis of fct-FePt nanoparticles of the order of 3–4 nm in diameter through the coreduction of iron and platinum ions in a polyol has been explored. We have succeeded in the synthesis of face-centered cubic structured 3–4 nm diameter FePt particles whose composition was very close to Fe 50 Pt 50. The Fe:Pt ratio was influenced little by the molar ratios of Fe and Pt acetylacetonate dissolved in ethylene glycol. However, depending on the polyol/Pt ratio, the as-prepared samples were either superparamagnetic or ferromagnetic. The transitiontemperature (T t ) and magnetic properties of the as-prepared FePt were very sensitive to the reaction conditions, and the T t varied between 593 and 893 K and the particles were ferromagnetic. The as-prepared FePt under the optimum condition had a T t as low as 593 K and H c as high as 1.11 kOe at an applied field of 1 T at room temperature. Furthermore, when the as-prepared FePt nanoparticles with T t around 593 K were annealed at 673 K in H 2 / N 2 atmosphere for an hour they transformed to the ordered fct (L1 0 ) structure with coercivity as high as 4.2 kOe at 300 K. This confirmed the lowering of T t by the manipulation of the reaction condition alone.