Compositionally controlled FePt nanoparticle materials

High temperature solution phase decomposition of Fe(CO)5 and reduction of Pt(acac)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)5 to Pt(acac)2, and the compositions ranging from Fe30Pt70 to Fe80Pt20 are obtained. The nanoparticle materials are easily dispersed into alkane solvent, facilitating their self-organization into nanoparticle superlattices. As synthesized FePt nanoparticles possess disordered fcc structure and show superparamagnetic behaviour. Thermal annealing induces the change of internal particle structure and thus the magnetic properties of the particles. Composition dependent structure analysis shows that an annealed FePt nanoparticle assembly with a composition around Fe55Pt45 will lead to the highly ordered fet phase. This Fe55Pt45 nanoparticle assembly yields high coercivity, and will be a candidate for future ultra-high density magnetic recording media applications.