Microstructures and magnetic domain structures in Sm2(Fe,Mn)17Nδ powders studied by analytical electron microscopy and Lorentz microscopy

Microstructures and magnetic domain structures of Sm2(Fe,Mn)17Nδ (δ=0, 3.4, 4.2, 5.0) powders are investigated by analytical electron microscopy and Lorentz microscopy, respectively. It is found that amorphous phases form with the addition of nitrogen and the area of the amorphous phases increases with the increase in nitrogen content. By elemental mapping with electron energy-loss spectroscopy (EELS), it is elucidated that the amorphous phase is enriched with N and Mn, while the crystalline phase is enriched with Fe. The analysis with Lorentz microscopy reveals that the size of the magnetic domains decreases with the increase in nitrogen content. Further, it is clarified that the domain walls exist on the Mn-enriched amorphous phases. Finally, the domain wall pinning in the amorphous boundary regions is considered to result in a large coercivity (1.04 MA/m) in Sm2(Fe,Mn)17N5.0 powder.