Synthesis and self-assembly of monodispersed cobalt-platinum, iron-cobalt-platinum, iron-paladium, and iron-platinum nanoparticles

Iron platinum (FePt) alloy nanoparticles were synthesized by simultaneous chemical reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl. Similarly, iron cobalt platinum (FeCoPt) alloy nanoparticles were synthesized by simultaneous chemical reduction of platinum acetylacetonate and cobalt acetylacetonate and thermal decomposition of iron pentacarbonyl; iron palladium (FePd) alloy nanoparticles were prepared by simultaneous chemical reduction of palladium acetylacetonate and thermal decomposition of iron pentacarbonyl; and cobalt platinum (CoPt) nanoparticles were obtained by the simultaneous chemical reduction of platinum acetylacetonate and the thermal decomposition of cobalt tricarbonyl nitrosyl. Their composition, surface chemistry, crystalline structure, particle morphology, and magnetic properties were characterized. The as-prepared particles were superparamagnetic and had a distorted fcc structure. The average diameter for the FePt particles was 3.0 nm, while for the FeCoPt, FePd, and CoPt particles were 3.5, 7.0, and 11.0 nm, respectively. The particles could be dispersed in hydrocarbon solvents and formed films consisting of hexagonal close-packed particles on carbon-coated copper TEM grids or silicon wafers. After annealing above 550°C, FePt and FeCoPt film transformed to the tetragonal (L1₀) phase. Only after annealing at 700°C for three hours did the Co₄₈Pt ₅₂ films transform to the L1₀ phase. However, the Co ₄₈Pt₅₂ films also experienced phase separation. There was no obvious evidence for the tetragonal phase for the films containing Fe ₅₀Pd₅₀ particles after annealing at temperature between 550°C–700°C. The order parameter and coercivity of the annealed films varied with composition and increased with increasing annealing temperature and time. After annealing at 700°C for 30 minutes, the coercivity of Fe₄₈Pt₅₂ film increased to over 11.6 kOe. However, the particle size increased to 16 nm due to sintering.