Self-assembly of superparamagnetic magnetite particles into peapod-like structures and their application in optical modulation

Superparamagnetic Fe3O4/SiO2/TiO2 peapod-like nanostructures have been successfully synthesized by using Fe3O4/SiO2 core/shell particles as building blocks and TiO2 as the adhesive without the need of any hard or soft templates. The fabrication process involves chaining the Fe3O4/SiO2 cores during magnetic stirring and subsequent fixing of the chain structure during TiO2 coating. The number of Fe3O4/SiO2 cores arranged linearly in the chains could be effectively controlled by tuning the amount of titanium precursor or the magnetic stirring rate. The double layer coating of SiO2 and TiO2 enhances thermal and chemical stability of the nanopeapods, and the one-dimensional chain structure produces interesting properties that enable applications not possible with conventional magnetite materials. As a demonstration, we show here the use of these superparamagnetic peapod-like nanostructures for low-frequency optical modulation.