Anomalous superconducting properties in the weak-ferromagnetic superconductors RuSr2GdCu2O8and RuCa2PrCu2O8

Anomalous superconducting properties are reported through transport, magnetic, and x-ray absorption near-edge spectroscopy (XANES) studies on the weak-ferromagnetic superconductors RuSr(2)GdCUu(2)O(8) and RuCa2PrCU2O8. For RuSr2GdCu2O8 [T-m = 131 K, resistivity T-c(onset) = 56 K, T-c(zero) = T-c(dia) = 39 K], a spontaneous vortex state above To = 30 K and a weak Meissner state below To with a lower critical field Bcj(0) = 12 G is observed due to the weak dipole field (similar to 4 G) of the weak-ferromagnetic order. In RuCa(2)PrCu2O(8) (T-m = 47 K, possible T-c = 37 K), an anomalously large field-cooled diamagnetic shielding signal is observed below Tc. Both samples show mixed-valence Ru4/5+ character from XANES data.