Bifunctional FePt Core−Shell and Hollow Spheres:  Sonochemical\nPreparation and Self-Assembly

Abstract

The sonochemical preparation of FePt/SiO₂ and FePt/ZnS/SiO₂ core−shell and hollow microspheres,\nas well as their self-assembly into a quasi-monolayer, was demonstrated. Uniform FePt nanoparticles\ncan be deposited on silica microspheres modified with polyelectrolytes by a sonochemical process, using\niron and platinum acetylacetonates as metal precursors. The amine and carboxylic functional groups in\nthe polyelectrolyte layer provided nucleation sites for FePt nanoparticles. Alternatively, if the silica was\nprecoated with ZnS, the nucleation of FePt nanoparticles on the ZnS shell can occur. A high coercivity\nof 12 kOe for these microspheres was obtained after annealing. A bifunctional microsphere with both\nluminescence and magnetic properties could be generated after the FePt/ZnS/SiO₂ microsphere was\nannealed in a vacuum.