Magnetic properties and microstructure of isolated Fe-Pt nanoparticle-monolayer assembly by protective coating

In order to diminish coalescence and interparticle sintering during high-temperature annealing of Fe-Pt nanoparticle films above 700 K, carbon or hafnium oxide overcoats are deposited on the nanoparticle-monolayer films. TEM observations reveal that grains in the Fe-Pt nanoparticle-monolayers are kept to be 4 nm in size even after annealing at 873 K; the particle size is close to the crystallite size estimated using Scherrer´s formula as 4 nm from x-ray diffraction. In-plane coercivity of the monolayer films at room temperature is 4 kOe and much higher than that without any overcoats. Furthermore, the hafnium-oxide coated monolayer-film shows a high magnetocrystalline anisotropy (K_u=4×10⁷ erg/cm³) and a high K_u V/kT value of 39.2 at 300 K, indicating the Fe-Pt nanoparticle-monolayers have high thermal stability as magnetic recording media.