Li Yong, Pan Desheng, Zhou Yangtao, Kuang Qifeng, Wang Chinwei, Li Bing, Zhang Bingsen, Park Jihoon, Li Da, Choi Chuljin, Zhang Zhidong
Shenyang National Laboratory for Materials Science, Institute of Metal Research, and School of Materials Science and Engineering, University of Science and Technology of China, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, China.
National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.
Nanoscale. 2020 May 21;12(19):10834-10841. doi: 10.1039/d0nr02424d.
ε-Iron nitrides with the general formula ε-Fe3N1+x (-0.40 < x < 0.48) have been widely studied due to their interesting magnetism. However, the phase diagram of the Fe-N binary system indicates the absence of monophasic ε-Fe3N1+x (x < 0) compounds that are stable below their synthetic temperatures. Here, ε-Fe3N1+x (-0.12 ≤ x ≤ -0.01) nanoparticles with excellent thermal stability and magnetic properties were synthesized by a simple chemical solution method. The ε-Fe3N1+x nanoparticles with space group P6322 have excellent oxidation resistance due to a carbon shell with a thickness of 2-3 nm. NPD refinements suggest that the ε-Fe3N1+x nanoparticles possess a highly ordered arrangement of N atoms and their magnetic moments align parallel to the c axis. The Curie temperature (TC) and room temperature saturation magnetization (MS) increase with decreasing N content, which results in record-high TC (632 K) and MS (169.2 emu g-1) at x = -0.12, much higher than the magnetic properties of the corresponding bulk materials. The significant enhancements in the intrinsic magnetic properties and thermal stability of ε-Fe3N1+x are ascribed to chemically engineering the stoichiometry and N occupancy from the disordered to the ordered site.
通式为ε-Fe3N1+x（-0.40 < x < 0.48）的ε-氮化铁因其有趣的磁性而受到广泛研究。然而，Fe-N二元体系的相图表明不存在在合成温度以下稳定的单相ε-Fe3N1+x（x < 0）化合物。在此，通过一种简单的化学溶液法合成了具有优异热稳定性和磁性的ε-Fe3N1+x（-0.12 ≤ x ≤ -0.01）纳米颗粒。具有空间群P6322的ε-Fe3N1+x纳米颗粒由于存在厚度为2 - 3 nm的碳壳而具有优异的抗氧化性。中子粉末衍射精修表明，ε-Fe3N1+x纳米颗粒具有高度有序排列的N原子，且它们的磁矩平行于c轴排列。居里温度（TC）和室温饱和磁化强度（MS）随N含量的降低而增加，这导致在x = -0.12时达到创纪录的高TC（632 K）和MS（169.2 emu g-1），远高于相应块状材料的磁性。ε-Fe3N1+x的本征磁性和热稳定性的显著增强归因于对化学计量比和N占据情况进行化学工程调控，使其从无序位点转变为有序位点。
