Anisotropic Growth and Magnetic Properties of α″-Fe16N2@C Nanocones

Abstract

α″-Fe16N2 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)5 as the iron source and tetraethylenepentamine (TEPA) as the N/C source at low synthesis temperatures to fabricate carbon-coated tetragonal α″-Fe16N2 nanocones. Magnetocrystalline anisotropy energy is suggested as the driving force for the anisotropic growth of α″-Fe16N2@C nanocones because the easy magnetization direction of tetragonal α″-Fe16N2 nanocrystals is along the c axis. The α″-Fe16N2@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″-Fe16N2@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″-Fe16N2 nanocones from oxidation in air atmosphere. The α″-Fe16N2@C nanocones synthesized at 433 K show a room-temperature saturation magnetization of 82.6 emu/g and a coercive force of 320 Oe.

Innovative Method for the Mass Preparation of α″-Fe16N2 Powders via Gas Atomization

“…After the first report by Kim and Takahashi on the giant saturation magnetization of about 290 emu/g of the α -Fe 16 N 2 phase in the evaporated Fe-N thin film, many researchers have made sustained efforts on both the fundamental [8,9] and practical aspects of preparing of the α -Fe 16 N 2 material. Thus, several attempts have been successfully made to develop magnetic materials containing α -Fe 16 N 2 phase in the form of thin films [10][11][12][13], foils [14,15], rods [16], ribbons [17], nanocones [18], and nanoparticles and powders [19,20], by using different preparation methods. The reported values of saturation magnetizations were widely scattered from 230 to 315 emu/g and appeared to be inconsistent and sometimes contradictory.…”

The Influence of Preparation Parameters on the Morphology and Magnetic Properties of Fe-N Powders Obtained by the Gas Atomization Method

“…Encouraged by the promising magnetic properties demonstrated by thin films, researchers are interested in preparing bulk samples with the same promising magnetic properties as potential precursors for permanent magnets. Thus, magnetic materials containing the α -Fe 16 N 2 phase have been prepared in the form of thin films, foils, rods, ribbons, nanocones, nanopowders, and powders [21][22][23][24][25][26][27][28][29][30]. However, the most suitable precursors for the preparation of permanent magnets are materials in the form of powders or even nanopowders.…”

Core–Shell Magnetic Nanoparticles

“…In this Special Issue there are research articles that focus on the different types of core-shell magnetic nanoparticles, which have uses ranging from biomedical applications to corrosion stability [1,2]. Moreover, this Special Issue focuses on different synthetic and fabrication methodologies to obtain these types of hybrid structures [1][2][3][4], such as gas phase synthesis [4], colloidal methodologies [2], and mechanochemical preparation [1,4].…”