VALENCE FLUCTUATIONS IN TERNARY EUROPIUM COMPOUNDS

We outline the possibility to study europium valence fluctuations with the mu SR method and report on mu SR experiments on the intermetallic compounds EuPdAs and NdPdAs. Above a magnetic transition at 15 K the temperature dependence of the relaxation rate in the trivalent neodymi um system behaves like a typical localized moment system. In the valen ce fluctuating europium compound the zero field relaxation rate levels off at 1.0 mu s(-1) above 40 K. Furthermore, the relaxation enhanceme nt in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of t ypical strength is assumed and a valence fluctuation rate of 0.8 mu s( -1) at 200 K is derived. Below the magnetic transition at 5 K a disord ered spin freezing is concluded in EuPdAs.