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

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Abstract
Amorphous Eu80Au20, Gd80Au20 and Eu60Yb20Au20 alloys have been investigated by 151Eu Mossbauer spectroscopy over a range of temperatures (1.5 to 245K) and by 155Gd and 197Au 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 Eu2+ and Gd3+ 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.