Mixed valencies of Eu in intermetallic compounds with the CaCu5 structure

The Moessbauer spectra of EuNisub(x)Znsub(5-x) and EuNisub(x)Cusub(5-x) compounds are composed of three subspectra: one corresponding to Eu2+, one to Eu3+ and one to Eu in a mixed valence state. The mixed valency is interpreted in terms of fast fluctuations between 4f6 and 4f7 configurations. The energy necessary to make an interconfiguration excitation depends on the number of Ni neighbours of Eu, on x and on the temperature. Suceptibility measurements are consistent with the analysis of the Moessbauer experiments. The dependence of the magnetic hyperfine fields, the Curie temperatures and the isomer shifts on x, is discussed. (Auth.)