NMR studies of magnetic superconductor RuSr2RECu2O8 (RE=Gd, Eu and Y) Original Research Article

We have carried out 99/101Ru and 63/65Cu nuclear magnetic resonance experiments in order to investigate magnetic and electronic properties of the magnetic superconductor RuSr2RECu2O8 (RE=Gd, Eu and Y). The two kinds of 99/101Ru signals were observed in the magnetically ordered state for each system, suggesting a charge segregation of Ru5+ (S=3/2) and Ru4+ (S=1) ions in the RuO2 layers. The internal field at the Cu sites is revealed to be of the order of kilo Oe, indicating weak magnetic interactions between the CuO2 and RuO2 planes. The temperature dependence of nuclear spin-lattice relaxation time T1 of 63Cu in RE=Y shows a ‘spin gap’ like behavior, suggesting the system is under-doped.