Synthesis of ultrasmall ferromagnetic face-centered tetragonal FePt graphite core-shell nanocrystals

Abstract

A simple one-step chemical-vapor-deposition (CVD) method was used to synthesize ultrasmall ferromagnetic face-centered tetragonal (fct) FePt-graphite core-shell nanocrystals. The methane-loaded silica was dried and heated to 800°C under H2 and then subjected to methane CVD for carbon deposition on the FePt nanoalloy formed on silica. Energy-dispersive X-ray (EDX) analysis show Fe/Pt ratios of 40:60 for the 2.8-nm nanocrystals and 25:75 for the 1.9-nm nanocrystals, suggesting Pt richness in the particles. The FePt nanocrystals with partially broken carbon shells turned the color of the solution in HCl to yellow after the addition owing to the Fe etching. Magnetic hysterisis loops recorded for FePt nanocrystal samples at 5 and 300K show relatively high coercivities for small particle sizes, suggesting a high portion of fct-oredres nanocrystals.