The magnetism of rare earth intermetallics RFe4Al8

The YFe4Al8 and ErFe4Al8 intermetallics were studied by57Fe Mössbauer spectroscopy between 2 K and room temperature. The spectra are consistent with iron occupying 8f sites only. There is hardly any difference between corresponding spectra of YFe4Al8 and ErFe4Al8. The Néel temperatures (≈185 K) and saturation hyperfine fields (≈11 T) are practically the same, confirming that the presence of the additional rare earth magnetic sublattice has hardly any influence on the magnetism of the Fe sublattice. From the saturation hyperfine field a low moment of ≈0.7μB on the Fe ions is deduced. The Mössbauer spectra show that atTN not all Fe ions order magnetically, a fraction of Fe ions remaining in a magnetically non-ordered state. This non-ordered fraction diminishes when the temperature decreases, but never vanishes completely. This peculiar behaviour seems to be characteristic for allx=4 members of the RFexAl12−x series of alloys. Its origin is not understood at this stage. It might be connected with the complex Fe spin structure exhibited by thex=4 intermetallics and needs to be considered in interpretations of magnetic measurements.