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] [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 disordered fcc structure and show superparamagnetic behavior. 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 [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. Index Terms--FePt nanoparticle, high Ku FePt, magnetic recording, nanoparticle synthesis, self-assembly, thermal annealing.