Keywords: high density recording media, CoPt, FePt, FePtCu, nanoparticles, high anisotropy materials, self-assembly, granular thin films, nanotechnology
FePt and CoPt magnetic nanoparticles film for future high density data storage media
Controlled self-assembly of magnetic L10 FePt and CoPt nanoparticles has stimulated great interest recently and may serve as future ultrahigh-density data storage media. This article reviews chemical synthesis of self-assembled FePtCu nanoparticles film and fabrication of CoPt/C and FePt/C granular thin films by sputtering. Their novel structural characterisation and unique magnetic properties are also reviewed. Firstly, monodispersed nanoparticle arrays of FePtCu with varying composition were synthesized by chemical reduction of Pt and Cu reagents and thermal decomposition of Fe pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers. As prepared particles had FCC structure with an average diameter of 3.5 nm and were superparamagnetic. The particles were well dispersed in hydrocarbon solvents and could be self-assembled into two or three dimensions particles arrays with a variety of close-packing arrangements. Heat-treatment of the self-assembled films at temperatures above 550°C transformed the particles from the FCC to the L10 phase, giving in-plane coercivities as high as 9 kOe. X-ray diffraction revealed that the Cu remained in the annealed FePtCu films. The magnetic hysteresis curves could be decomposed into a hard component (Hc > 5 kOe) and a soft component (Hc < 2 kOe). On the other hand, CoPt and FePt nanoparticles embedded in non-magnetic C matrix have been obtained by annealing CoPt/C and FePt/C multilayer precursors deposited onto Si substrate at different substrate temperature. The magnetic and structural properties of the films were investigated with respect to bilayer thickness, annealing conditions and temperature. Ordered FePt nanoparticles with average particle size from a few nanometers to about 20 nm were obtained directly by depositing at high substrate temperature. These particles showed higher magnetic ordering than particles made via multilayer precursors. With a certain FePt to C ratio, films showed strong perpendicular anisotropy.