Preparation and characterization of hollow hybrid magnetic microspheres

The ionic poly(St-co-MAA) microsphere with about 250 nm diameter was prepared by soap-free emulsion polymerization. Then, the Fe₂O₃/SiO₂/poly(St-co-MAA) core/shell sphere was prepared by chemical co-precipitation and followed by a sol-gel method. Finally, the hollow SiO₂/Fe₂O₃ spheres were formed by tetrahydrofuran (THF) solvent treatment. The TEM photographs of core/shell spheres and hollow spheres shows that the poly(St-co-MAA) microspheres have a smooth surface and their diameter is about 250 nm. The XRD patterns of the hollow SiO₂/Fe spheres are obtained at various reduction times. When the reduced time is increasing, the relative intensities of diffraction peaks increases and the saturation magnetization and remnant magnetization values increased. And the H_c is also increased.