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

epsilon-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 degrees C, followed by annealing at 573 K. Nanostructured and monophasic oxygen-free iron nitride, epsilon-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 mu(B)/Fe and a Curie temperature of 500 K. T-c is lower than that of bulk epsilon-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-FexOy 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.