Nanoscale Iron Nitride, ε‑Fe₃N: Preparation from Liquid Ammonia and Magnetic Properties

ε-Fe₃N shows interesting magnetism but is difficult to obtain as a pure and single-phase sample. We report a new preparation method using the reduction of iron­(II) bromide with elemental sodium in liquid ammonia at −78 °C, followed by annealing at 573 K. Nanostructured and monophasic oxygen-free iron nitride, ε-Fe₃N, is produced according to X-ray diffraction and transmission electron microscopy experiments. The magnetic properties between 2 and 625 K were characterized using a vibrating sample magnetometer, revealing soft ferromagnetic behavior with a low-temperature average moment of 1.5 μ_B/Fe and a Curie temperature of 500 K. T_C is lower than that of bulk ε-Fe₃N (575 K) [Chem. Phys. Lett 2010, 493, 299], which corresponds well with the small particle size within the agglomerates (15.4 (±4.1) nm according to TEM, 15.8(1) according to XRD). Samples were analyzed before and after partial oxidation (Fe₃N–Fe_xO_y core–shell nanoparticles with a 2–3 nm thick shell) by X-ray diffraction, transmission electron microscopy, electron energy-loss spectroscopy, and magnetic measurements. Both the pristine Fe₃N nanoparticles and the oxidized core–shell particles showed shifting and broadening of the magnetic hysteresis loops upon cooling in a magnetic field.