A low temperature and solvent-free direct chemical synthesis of L10 FePt nanoparticles with size tailoring

The FePt alloy in the high magnetic anisotropy L10 phase is one of the most promising magnetic materials in many applications, including ultra-high-density magnetorecording. A new green chemical approach to synthesize magnetically hard L10 FePt nanoparticles is described in this paper by using crystalline saline complex hexaaquairon(II)hexachloroplatinate, [Fe(H2O)6]PtCl6, as the precursor. The crystal structure of this complex shows alternate layers of Fe and Pt atoms. After ball milling, annealing at 400 °C under a reducing atmosphere leads to the direct formation of FePt nanoparticles in the highly ordered L10 phase. This method is a green synthesis due to the low temperature for phase transformation, and the absence of organic solvents or surfactants in the reaction. Indeed the milling step is performed using NaCl as media, which can be easily removed with water. By varying the precursor/NaCl ratio, particles with size in the range of 6.2-13.2 nm were obtained. With the decrease of particle size, the room temperature coercivity of FePt nanoparticles also decreased from 10.9 kOe to 4.7 kOe.