Iron oxide nanochains coated with silica: Synthesis, surface effects and magnetic properties

Investigation and synthesis of anisotropic magnetic nanostructures, such as wires, rods, fibers, tubes and chains, is an important field of research due to the beneficial properties and great potential for practical applications ranging from magnetic data storage to biomedicine. Silica coated iron oxide nanochains of length up to 1 mu m and diameter similar to 80-100 nm have been synthesized by the simultaneous magnetic assembly of superparamagnetic iron oxide nanoparticle clusters (SNCs) as links (viz. maghemite, gamma-Fe2O3) and the fixation of the assembled SNCs with an additional layer of deposited silica. We reveal that is possible to achieve either superparamagnetic or ferromagnetic behavior with the nanochains depending only on their physical orientation. The superparamagnetic behavior is observed for random orientation of nanochains whereas ferromagnetic properties (H-c approximate to 100 Oe) come to the fore when the orientation is mainly parallel. These peculiar magnetic properties can be related to: (1) the specific size, which is similar to 9 nm, of primary building blocks of the nanochains, i.e. of maghemite nanoparticles; (2) to the anisotropic chain-like shape of the particles; and (3) to inter-particle interactions. Large pore volume and pore size of silica shell as well as good colloidal stability and magnetic responsiveness of such nanochains enable applications in biomedicine.