Spin-glass ordering and absence of valence fluctuations of Eu in EuCu2Si2 single crystals

The results of x-ray diffraction, dc and ac magnetic susceptibilities, and E151u Mössbauer spectroscopy studies of single crystals of EuCu₂Si₂ grown by a flux method are reported. The magnetic susceptibility and Mössbauer data clearly demonstrate the divalent state of Eu in the temperature range 1.9-298.2 K, in contrast to an intermediate-valence state of Eu observed for polycrystalline samples. These data also show that, contrary to earlier reports, the EuCu₂Si₂ compound is a spin glass.