Improvement of the magnetic properties of new compound SmFe_7 by nitrogenation

点击翻译按钮获取中文摘要

SmFe_7 is known to have large spontaneous magnetic moment and magnetocrystalline anisotropy, which are equivalent to those of NdFeB hard magnetic material. However, although single crystal of SmFe_7 was obtained by a flux method, polycrystalline specimen has not been obtained. This seems to be due to that SmFe_7 phase exists in a narrow composition and temperature region. This study was performed to identify SmFe_7 phase in the phase diagram of Sm-Fe system, to improve magnetic properties by nitrogenation or substitution, and to search new materials in Sm-Fe system. SmFe_7 phase was identified by x-ray diffraction studies for arc-melted specimens that were annealed at 900℃〜1200℃ and quenched into water. It was revealed that SmFe_7 phase appears at temperatures between 1030℃〜950℃. However, it was unsuccessful to obtain single SmFe_7 phase.Nitrogenation of SmFe_7 crystal was unsuccessful. This is due to the oxidation of Sm. It is well known that Sm is the most oxidizable metal in the rar … More e-earth metal. When SmFe_7 crystal was heated in the stream of nitrogen gas, it was oxidized easily by the residual oxygen even at lower temperatures below 400℃ and decomposed. To overcome this difficulty new annealing system, which can be evacuated to a vacuum level more than 10^<-7> Torr, is necessary. However, we could not equip these type of system at present study. Therefore, we studied the effect of substitution of non-magnetic Al to the crystallographic and magnetic properties of SmFe_7 by comparing with the effect to other compounds in the Sm-Fe system. It was for the first time to study Al substitution effect systematically by using single crystal specimens of various phases in Sm-Fe system. Although Al substitution decreases saturation moment of Sm-Fe compounds, it is effective to increase Curie temperature and magnetocrystalline anisotropy. Moreover, in the process of crystal growth of SmFe_3, new compound with a formula of Sm_6Fe_<23> was discovered in this study. Sm_6Fe_<23> contains a lot of Fe atoms in unit cell, and, therefore, it is very interesting as a practical magnetic material. Less