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

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• 作者：Anne-Marie Zieschang ; Joshua D. Bocarsly ; Michael Dürrschnabel ; Leopoldo Molina-Luna ; Hans-Joachim Kleebe ; Ram SeshadriBarbara Albert
• 刊名：Chemistry of Materials
• 出版年：2017
• 出版时间：January 24, 2017
• 年：2017
• 卷：29
• 期：2
• 页码：621-628
• 全文大小：610K
• ISSN：1520-5002

文摘

ε-Fe<sub>3sub>N 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-Fe<sub>3sub>N, 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<sub>Bsub>/Fe and a Curie temperature of 500 K. T<sub>Csub> is lower than that of bulk ε-Fe<sub>3sub>N (575 K) [ Chem. Phys. Lettinstance" xml:space="preserve"> 2010instance" xml:space="preserve">, 493instance" xml:space="preserve">, 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 (Fe<sub>3sub>N–Fe<sub>xsub>O<sub>ysub> 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 Fe<sub>3sub>N nanoparticles and the oxidized core–shell particles showed shifting and broadening of the magnetic hysteresis loops upon cooling in a magnetic field.