Magnetic force microscopy (MFM) study of FePt nanocrystals overcoated with silica

Chemically-synthesized FePt nanocrystals must be annealed at $\sim $550C to induce the hard magnetic L10 phase.~ Sintering of nanocrystal films occurs at these temperatures, resulting in the loss of control over nanocrystal size and separation in the film.~ We have developed a silica overcoating strategy to prevent nanocrystal sintering.~ In this study, 6 nm diameter FePt nanocrystals were coated with 20 nm thick shells of silica using an inverse micelle process.~ Magnetization measurements of the annealed FePt@SiO2 nanocrystals indicate ferromagnetism at room temperature.~ The micromagnetic properties of thin films of these nanocrystals were studied using MFM.