Xiaocao Hu

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.

Direct liquid phase synthesis of ordered L10 FePt colloidal particles with high coercivity using an Au nanoparticle seeding approach

Ordered L10 and high coercivity FePt nanoparticles were successfully synthesized via a chemical method using pre-synthesized Au nanoparticles as nuclei seeds. The size of the Au nanoparticles seems to play a significant role in the formation of the tetragonal phase (L10) FePt colloidal nanoalloys. Seeding with ∼12 nm diameter monodispersed Au nanoparticles in the reaction mixture was found to lead to partial L10 FePt particles with 2.8 kOe coercivity at room temperature, while seeding with ∼6 nm Au nanoparticles leads to the formation of well L10 ordered FePt colloidal particles with 8.8 kOe coercivity at room temperature, one of the highest values for the direct liquid phase synthesis of L10 FePt colloidal particles. Furthermore, seeding with smaller Au particles decreases the ordering temperature from 360 °C to 300 °C leading to the formation of more uniform well-shaped nanoparticles.