Reduction of the fcc to L1₀ Ordering Temperature for Self-Assembled FePt Nanoparticles Containing Ag

Abstract

[Fe 49 Pt 51 ] 88 Ag 12 nanoparticles were prepared by the simultaneous polyol reduction of platiunum acetylacetonate and silver acetate and the thermal decomposition of iron pentacarbonyl, giving 3.5 nm diameter FePt particles with Ag atoms substituted in the lattice. The addition of Ag promoted the fcc to tetragonal phase transition, thereby reducing the temperature required for this transition by some 100 to 150 °C compared with pure FePt nanoparticles. After heat treatment at 400 °C for 30 min, the coercivity of the films containing [Fe 49 Pt 51 ] 88 Ag 12 nanoparticles was more than 3400 Oe, while the films containing FePt nanoparticles were superparamagnetic. This decrease in phase transformation temperature allowed us to decrease the particle coalescence and loss in particle positional order seen when FePt nanoparticles were transformed at temperatures above 550 °C.