NMR evidence for coexistence of superconductivity and ferromagnetic component in magnetic superconductor RuSr2YCu2O8:: 99,101Ru and 63Cu NMR

From Ru- and Cu-NMR studies, we present evidence for coexistence of superconductivity and ferromagnetism in a cuprate superconductor RuSr2YCu2O8 (RuY1212). The observation of a large enhancement of a radio-frequency field for the Ru-NMR signal at zero field reveals the existence of a ferromagnetic (FM) component in the ordered RuO2 plane below a Curie temperature of T-M = 150 K. Just below the onset temperature of superconductivity T-c(onset) = 45 K, a remarkable decrease of the nuclear spin-lattice relaxation rate 1/T-1 was observed within the ordered RuO2 plane as well as the CuO2 plane, revealing that the superconducting gap coexists with the FM component in the RuO2 plane on a microscopic scale. In addition, from the observation of a sharp peak in (101)(1/T-1) at T-c(zero) similar to 23 K where the resistivity becomes zero, we suggest that the motion of self-induced vortices originating from fluctuations of the FM component induces the resistivity between T-c(onset) and T-c(zero) in RuY1212.