NMR Evidence for Coexistence of Superconductivity and Ferromagnetic Component in Magnetic SuperconductorRuSr2YCu2O8:R99,101uandC63uNMR

From Ru- and Cu-NMR studies, we present evidence for coexistence of superconductivity and ferromagnetism in a cuprate superconductor ${\mathrm{RuSr}}_2{\mathrm{YCu}}_2{\mathrm{O}}_8$ (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 ${\mathrm{RuO}}_2$ plane below a Curie temperature of $T_M=150\mathrm{}\mathrm{K}$. Just below the onset temperature of superconductivity $T_c^{\mathrm{onset}}=45\mathrm{}\mathrm{K}$, a remarkable decrease of the nuclear spin-lattice relaxation rate ${1/T}_1$ was observed within the ordered ${\mathrm{RuO}}_2$ plane as well as the ${\mathrm{CuO}}_2$ plane, revealing that the superconducting gap coexists with the FM component in the ${\mathrm{RuO}}_2$ plane on a microscopic scale. In addition, from the observation of a sharp peak in ${}^{101}\left({1/T}_1\right)$ at $T_c^{\mathrm{zero}}\sim 23\mathrm{K}$ 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 $T_c^{\mathrm{onset}}$ and $T_c^{\mathrm{zero}}$ in RuY1212.