Chemical synthesis of monodisperse Fe-Ni nanoparticles via a diffusion-based approach.

We report a chemical route for the preparation of monodisperse Fe-Ni nanoparticles with tunable compositions and sizes. Unlike commonly used synthetic approaches that involve the simultaneous reduction of metal precursors in the presence of reducing agents, the approach developed in this study utilizes pre-formed Ni nanoparticles to react with Fe(III) acetylacetonate in high boiling-point solvents, wherein newly-generated Fe atoms diffuse into Ni nanoparticles to form Fe-Ni nanoparticles. The analytic results of powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the as-synthesized Fe-Ni nanoparticles possess a face-centered cubic (fcc) crystalline structure and have a spherical or near-spherical morphology. X-ray photoelectron spectroscopy (XPS) study reveals metallic characteristics for the chemical state of Fe and Ni. The particle morphology and size distribution of the as-synthesized Fe-Ni nanoparticles are regulated by the pre-formed Ni nanoparticles, while the composition can be adjusted to some extent by the ratio of Fe precursor to Ni nanoparticles. Magnetic measurements reveal a superparamagnetic characteristic above the blocking temperature for the as-synthesized Fe-Ni nanoparticles. The synthetic approach may also be applied to other bimetallic nanoparticle systems.