TEM and XAS characterization of hard magnetic phase in Nd-Fe alloys

Nd₈₀Fe₂₀ alloys were prepared by copper mold casting and directional solidification (DS) to obtain a coarse microstructure, which can be identified unambigously. The mold-cast samples exhibit a fine globular eutectic structure and show high room temperature coercivity (∼ 5 kOe). Transmission electron microscopic (TEM) investigations reveal the presence of fcc (a = 5.32 Å) Nd-rich and nanocrystalline non-cubic Fe-rich phases. The directionally solidified (DS) samples exhibit large grains (composition close to NdFe₂). The NdFe₂ grains (formed in the DS samples) show clear magnetic domains with uniaxial anisotropy indicating that the NdFe₂-type phase observed in the present samples is not a cubic phase. X-ray absorption spectroscopy (XAS) was used to analyze the local configuration around Fe atoms in the mold-cast samples. The XAS patterns do not match with the bcc and fcc standards, which supports the presence of NdFe ₂ phase with uniaxial symmetry in the DS samples.