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

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.