Mössbauer Spectroscopy on Superconducting and Mixed Valent Europium Compounds

Abstract

Mössbauer spectroscopy has been applied to investigate Eu_zSn_1−zMo₆S₈ and (ScEu)Al₂. The former compound is superconducting for z lt; 0.9. Its ¹⁵¹Eu Mössbauer spectra show a magnetic hyperfine splitting at T lt; 0.5 K, and in addition a single line at T > 0.1 K. The behavior is considered to result from spin-glass type magnetic ordering. The linewidth of the single line increases by about a factor of three from 300 K to 0.15 K, and its isomer shift indicates a very low conduction electron density at the Eu site. The ¹⁵¹Eu Mössbauer spectra of (ScEu)Al₂ show a line whose position changes from −5.8 mm/sec at 325 K to −1.9 mm/sec at 4.2 K. This change results from a change of the valence of the mixed valent Eu impurity ions in ScAl₂ from (2.34 ± 0.05) to (2.73 ± 0.07) as the temperature is decreased. For the valence fluctuations we obtain a fluctuation temperature of (50 ± 10) K and an excitation energy of (280 ± 40) K.