Large-scale synthesis of high-content Fe nanotubes/nanorings with high magnetization by H₂ reduction process

High-content Fe hollow nanostructures from nanotubes (NTs) to nanorings (NRs) have been successfully fabricated by reduction of α-Fe ₂O₃ hollow nanostructures at designated temperature. We investigated the influence of reduction condition on the structure and property of the products. With increasing reduction temperature, α-Fe ₂O₃ with rhombohedral phase could be converted to cubic inverse spinel phase Fe₃O₄. Thereafter the phase was converted to the dominant cubic Fe preserving the same morphology. The highest M_s is 126 emu/g and 123 emu/g for 70 nm NRs and NTs reduced at 450 °C, respectively. Our results provide a general strategy of reducing single-crystalline α-Fe₂O₃ hollow nanostructures to get high magnetization which is required for many applications.