Coexistence of ferromagnetism and superconductivity in magnetic superconductor RuSr2YCu2O8 revealed by Cu-63-NMR

Cu-63-NMR measurement has been performed to investigate the coexistence of superconductivity and ferromagnetism in a hybrid ruthenium (Ru)-copper (Cu) oxide superconductor RuSr2YCu2O8 (RuY1212). Broadening of the Cu-NMR signa l below Tm demonstrates that Cu nuclei in CuO2 planes feel a dipolar field from ordered Ru moments in RuO2 planes. On the other hand, the opening of t he SC gap is confirmed from the observation of a decrease in the nuclear sp in-lattice relaxation rate, (63)l/T-l below T-c(onset) = 45 K. These NMR re sults provide evidence that the superconductivity coexists with the (field induced) ferromagnetism at a microscopic scale. We also found that the T de pendence and the magnitude of l/TlT are quite similar to those in YBa2Cu3O7 (Y1237), indicative of the same spin-fluctuation character in both compoun ds. This suggests that the hole content in RuY1212 is comparable to that in Y1237. (C) 2001 Elsevier Science B.V. All rights reserved.