PREPARATION AND PROPERTIES OF FERROMAGNETIC FePt DISPERSION

K. Sato, B. Jeydevan , K. Tohji.

Dowa Mining Company, Daiichi Tekko Building, 1-8-2 Marunouchi, Chiyoda-ku, Tokyo 100-8282 Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan.

In most cases, the magnetic fluid is a dispersion of superparamagnetic iron oxide nanoparticles in water or in an organic solvent. Magnetic fluids dispersing metallic and alloy nanoparticles have been attempted in the past. However, the phase stability of these particles in oxidizing atmosphere has been a serious impediment for their use in any industrial applications. The superparamagnetic and chemically disordered fee FePt particles synthesized via chemical route are considered to be a consequence of the fast reaction kinetics. Therefore, it is believed that the direct synthesis of chemically ordered fee structure is possible through finer control of the reaction kinetics. Is this paper, we describe the preparation of ferromagnetic FePt particles dispersed in hexane-based suspension.

Specified amounts of Fe acetylacetate and Pt acetylacetat precursors were dissolved in 100 ml of tetraethylene glycol (TEG) in a reaction vessel with a reflux attachment and placed in a mantle heater and heated at constant rate under gentle mechanical stirring and the suspensions was refluxed for three and a half hours at specific temperatures between 533 and 573 K at 10 K interval. During this stage, generally, the pale yellow colored solution turned colorless and finally black suggesting theformation of FePt particles. The FePt particles thus produced were recover by cenrtifuging the suspension for analysis.

The particles synthesized were of about 5 – 6 nm in diameter. The saturation magnetization and coercitivy were around 50 emu per gram and 2000 Oe respectively. The particles synthesizing in polyol medium were dispersed in hexane by using solvent-solvent extraction using appropriate surfactants. The TEM micrograph of the dispersed particles is shown in Figure 1. The details of the preparation and the magnetic properties of this dispersion will also be reported and discussed.