Chemically synthesized L1₀-Type FePt nanoparticles and nanoparticle arrays via template-assisted self-assembly

Chemically ordered L1₀-type FePt nanoparticle agglomerates were synthesized directly by the co-reduction of Fe(III) and Pt(II) acetylacetonates in tetraethylene glycol at 300°C in the absence of surfactants. These nanoparticles could be dispersed in n-hexane by coating with oleic acid and oleylamine. However, the dispersed particles exhibited only chemically disordered fee phase and superparamagnetic behavior. The FePt nanoparticle film composed of dispersed particles and stabilized using amino-silane began to structurally transform to ordered L1₀ phase at 600°C, which is lower compared to that prepared by the hot soap method. Rotational hysteresis loss measurement suggested that the ordering was incomplete at 600°C and the nanoparticle film had the distribution of magnetocrystalline anisotropy field values. The FePt nanoparticle array was fabricated using the template-assisted self-assembly technique. To produce periodic dots on a substrate, positive-biased pulse voltage was applied to the substrate coated with octadecyltrichlorosilane monolayer by using a conducting cantilever used in a scanning probe microscope. This process induced electrochemical modification of -CH₃ groups into polar ones. The resulting template had well-aligned sub-100-nm dot arrays with sub-100-nm periodicity. The FePt nanoparticles were fixed on the patterned areas selectively.