Preparation and properties of magnetic iron oxide nanotubes

Magnetite (Fe3O4) nanotubes were prepared by reducing synthesized hematite (α-Fe2O3) nanotubes in 5% H2+95% Ar atmosphere, and then maghemite (γ-Fe2O3) nanotubes were obtained by re-oxidizing the Fe3O4 nanotubes. The nanotube structure was kept from collapsing or sintering throughout the high temperature reducing and re-oxidizing processes. The coercivities of the Fe3O4 and γ-Fe2O3 nanotubes synthesized were found to be 340.22 Oe and 342.23 Oe, respectively, both higher than other nanostructures with the same phase and of similar size. Both adsorbed phosphate and the nanotube structure are considered responsible for this high coercivity.