Compositionally controlled FePt nanoparticle materials

High temperature solution phase decomposition of Fe(CO)/sub 5/ and reduction of Pt(acac)/sub 2/ in the presence of stabilizers, oleic acid and oleyl amine, are employed to produce 4 nm diameter FePt nanoparticles. The Fe and Pt composition of the nanoparticle materials can be tuned by adjusting the molar ratio of Fe(CO)/sub 5/ to Pt(acac)/sub 2/, and the compositions ranging from Fe/sub 30/Pt/sub 70/ to Fe/sub 80/Pt/sub 20/ are obtained. The nanoparticle materials are easily dispersed into alkane solvent, facilitating their self-organization into nanoparticle superlattices. As synthesized FePt nanoparticles possess a disordered fcc structure and show superparamagnetic behavior. Thermal annealing induces a change of internal particle structure and thus of the magnetic properties of the particles. Composition dependent structure analysis shows that an annealed FePt nanoparticle assembly with a composition around Fe/sub 55/Pt/sub 45/ will lead to the highly ordered fct phase. This Fe/sub 55/Pt/sub 45/ nanoparticle assembly yields high coercivity, and will be a candidate for future ultra-high density magnetic recording media applications.