Mossbauer investigations of amorphous RE80Au20alloys (RE=Eu2+, Gd3+)

Amorphous Eu 80 Au 20 , Gd 80 Au 20 and Eu 60 Yb 20 Au 20 alloys have been investigated by 151 Eu Mossbauer spectroscopy over a range of temperatures (1.5 to 245K) and by 155 Gd and 197 Au Mossbauer spectroscopy at 4.2K (ordered state). In all cases, electric-field gradients (EFG) have a well defined sign; neither isomer shifts nor EFG present significant distributions. This indicates strict compositional and structural short-range order around both rare-earth and Au atoms. Previous magnetisation measurements have revealed dominant ferromagnetic interactions with a small reduction of the spontaneous moment due to asperomagnetism. Consistent with the absence of single-ion anisotropy and with the amorphous arrangement, the principal direction of the EFG tensor is random with respect to the hyperfine field at all atomic components. The distribution of the Eu 2+ and Gd 3+ magnetic hyperfine field is interpreted in terms of anisotropic conduction electron polarisation, correlated with spin misalignment at these sites, since the transferred field at Au presents no distribution.