| Summary: | α″-Fe<sub>16</sub>N<sub>2</sub> nanomaterials with a shape anisotropy for high coercivity performance are of interest in potential applications such as rare-earth-free permanent magnets, which are difficult to synthesize in situ anisotropic growth. Here, we develop a new and facile one-pot microemulsion method with Fe(CO)<sub>5</sub> as the iron source and tetraethylenepentamine (TEPA) as the N/C source at low synthesis temperatures to fabricate carbon-coated tetragonal α″-Fe<sub>16</sub>N<sub>2</sub> nanocones. Magnetocrystalline anisotropy energy is suggested as the driving force for the anisotropic growth of α″-Fe<sub>16</sub>N<sub>2</sub>@C nanocones because the easy magnetization direction of tetragonal α″-Fe<sub>16</sub>N<sub>2</sub> nanocrystals is along the c axis. The α″-Fe<sub>16</sub>N<sub>2</sub>@C nanocones agglomerate to form a fan-like microstructure, in which the thin ends of nanocones direct to its center, due to the magnetostatic energy. The lengths of α″-Fe<sub>16</sub>N<sub>2</sub>@C nanocones are ~200 nm and the diameters vary from ~10 nm on one end to ~40 nm on the other end. Carbon shells with a thickness of 2–3 nm protect α″-Fe<sub>16</sub>N<sub>2</sub> nanocones from oxidation in air atmosphere. The α″-Fe<sub>16</sub>N<sub>2</sub>@C nanocones synthesized at 433 K show a room-temperature saturation magnetization of 82.6 emu/g and a coercive force of 320 Oe.
|
|---|