FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles

We present a simple fabrication of FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles. 5 nm FePt nanoparticles were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleylamine as stabilizers. The as-synthesized FePt nanoparticles can self-organize well on a clean SiO/Si substrate and, then, were annealed in a vacuum using a rapid thermal process at different temperatures for 0.5 h. It is found that the annealing temperature plays a key role in determining the final products. The samples annealed at $\text{550\hspace{0.05em}°}\mathrm{C}$ and $\text{700\hspace{0.05em}°}\mathrm{C}$ consist of a FePt-face-centered-tetragonal (fct) phase with a coercivity of around 1000 and 8800 Oe, respectively, whereas, the samples annealed at $\text{580\hspace{0.05em}°}\mathrm{C}$ are composed of two phases: one is the FePt-fct phase and the other is a Fe-body-centered-cubic phase. The hysteresis loop of the sample annealed at $\text{580\hspace{0.05em}°}\mathrm{C}$ is also two-phase like with a kink at low field and its coercivity is around 8000 Oe. That indicates that Fe can be segregated from FePt by proper annealing, forming FePt and Fe nanocomposites.