Fabrication of FePt/SiO₂ composite magnetic beads

The present paper describes effects of organic molecules such as polymers and low molecular surfactants for chemical synthesis of magnetic core-shell FFePt/SiO₂ composite microspheres for biomedical applications such as the magnetic hyperthermia and the magnetically guided drug delivery system in cancer therapy. We obtained FePt/SiO₂ composite microspheres approximately 330 nm in diameter with a thin shell of 5 nm in thickness by synthesizing FePt nanoparticles on silica microspheres modified with polydiallyldimethylammonium chloride (PDDA). The magnetic shell of 5 nm in thickness is a nanohybrid composed of FePt nanoparticles of approximately 3-4 nm in size and a single-layer of the polymer. The FePt/PDDA/SiO₂ core-shell particles exhibit ferromagnetic features at room temperature because the Fe-Pt nanoparticles with ordered-alloy phase are formed with the aid of PDDA despite of small size. The blocking temperature depends on the synthesis temperature of FePt nanoparticles.