Magnetocrystalline anisotropy of partially ordered Fe-Pt nanoparticles directly synthesized with microwave-polyol method

We report direct synthesis of chemically ordered Fe-Pt nanoparticles using microwave irradiation during polyol reaction at 250/spl deg/C without any post-synthesis treatments. Mo/spl uml/ssbauer analysis exhibits the Fe-Pt nanoparticles having partially ordered L1/sub 0/ structure, and the fraction of Fe atoms in the chemically ordered L1/sub 0/ structure to the total amount of Fe atoms is 57%. Coercivity and saturation magnetization of the partially ordered Fe-Pt nanoparticles are 3.0 kOe and 57 emu/g at room temperature, respectively. An evaluation of the anisotropy-field distribution using Flanders-Shtrikman method reveals that the Fe-Pt sample includes nanoparticles with anisotropy fields much lower than the anisotropy field H/sub k//sup Wr/ of 85 kOe obtained by rotational hysteresis loss measurements.