Structure Optimization of FePt Nanoparticles of Various Sizes for Magnetic Data Storage

Surfactant-coated, fcc disordered FePt nanoparticles of three different sizes between 3 and 7 nm were prepared and washed according to a modified reaction route based on Sun et al. Hexane dispersions of nanoparticles were dried on transmission electron microscopy (TEM) grids, and the resulting monolayers were annealed by a sinter-free procedure at 600 C and at 650 C for 2 hours, respectively, developing the L10 phase while preserving their monodispersity. The order parameter of the L10 phase was measured using electron diffraction from statistically large ensembles of nanoparticles using an X-ray-like signal collection technique. The order parameter increases with particle size and with the temperature in the range 600 C to 650 C, being close to unity for the 7.2-nm particles annealed at 650 C for 2 hours.