Valence fluctuations in ternary europium compounds

We outline the possibility to study europium valence fluctuations with the μSR method and report on μSR 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 neodymium system behaves like a typical localized moment system. In the valence fluctuating europium compound the zero field relaxation rate levels off at 1.0\ μs^-1 above 40 K. Furthermore, the relaxation enhancement in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of typical strength is assumed and a valence fluctuation rate of 0.8 μs^-1 at 200 K is derived. Below the magnetic transition at 5 K a disordered spin freezing is concluded in EuPdAs. This revised version was published online in July 2006 with corrections to the Cover Date.     

μ+SR on ( La_1.85-x Ndx) Sr0.15 CuO_4

Below 30 K, magnetic order was found in La_1.85-x Nd_x Sr_0.15 CuO_4 with x ranging between 0.30 and 0.60. This order occurs in the low temperature tetragonal phase. Below 5 K, the interaction of Nd and Cu moments modifies the magnetic order in the Cu–O planes leading to an increase of the muon spin rotation frequency and the transverse damping rate. Even down to 0.1 K, considerable spin dynamics is observable. This revised version was published online in August 2006 with corrections to the Cover Date.