A New Green Chemical Synthesis Strategy for Synthesis of L10 FePt Nanoparticles from Layered Precursor Fe(H$_{2}$O)$_{6}$PtCl$_{6}$

In this work, a new green chemical strategy for the synthesis of L1$_{0}$ FePt nanoparticles is reported. The starting material is a polycrystalline molecular complex (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$, in which Fe and Pt atoms are arranged on alternating planes. The starting compound was milled with crystalline NaCl and then annealed under forming gas (5 {\%} H$_{2}$ and 95 {\%} Ar) at 450 $^{\circ}$C for 2h. Finally, the mixture was washed with water to remove the NaCl and L1$_{0}$ FePt nanoparticles were obtained. Transmission electron microscopy (TEM) images revealed that this method is able to produce L1$_{0}$ nanoparticles with different average size varying from 13.9 nm to 5.4 nm depending on the (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$/NaCl ratio. With smaller (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$/NaCl ratio(10mg/20g) and longer milling time(15h), FePt nanoparticles had a smaller size and narrower size distribution. The X-Ray Diffraction (XRD) pattern showed the presence of the characteristic peaks of the fct phase. The hysteresis loop, measured both at room temperature and 50 K, shows a high coercivity of 7.6 kOe and 11.2 kOe, respectively as expected for the high anisotropy L1$_{0}$ phase. Larger precursor/NaCl ratio and shorter ball milling time led to larger coercivity.