Charge and spin states of Ru and Cu in magnetic superconductor RuSr2GdCu2O8 studied by NMR

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Electronic and magnetic properties of RuSr2GdCu2O8 have been investigated by electric resistivity, magnetization,and Cu-, Ru-NMR measurements. Magnetic order (TM5133 K) and superconductivity[Ts(onset);52 K] have been confirmed. We observed two kinds of Ru-NMR signals (the hyperfine fields of101Ru are 590 kOe and 290 kOe), suggesting a charge segregation of Ru5+ (S-3/2) and Ru4+ (S=1) in theRuO2 layers. The hyperfine field at the Cu site is diminishingly small, indicating magnetic interactions betweenCuO2 and RuO2 layers are weak. Assuming that holes are inherently doped in the CuO2 layers from the (Ru4+,Ru5+)O2 layers, the high-Tc superconductivity can occur under weak magnetic interactions between Ru andCu spins in RuSr2GdCu2O8.