Superconductivity And Weak Ferromagnetic Order Of The New Ruca2rcu2o8+Delta (R = Pr, Nd, Sm, Eu, Gd) System

Superconducting onset temperatures T up to 23-44 K are reported for the new RuCa2RCu2O8+delta (R = Pr, Nd, Sm, Eu, Cd) system with a Ru-1212 RuCa2PrCu2O8+delta-type structure. Preliminary study indicates that the crystal structure is an orthorhombic distortion of the tetragonal RuSr2GdCU2O8+delta-type structure which has space group P4/mmm, T-m similar to 136 K, and T-c(max) similar to 65 K. With similar RuO6 octahedral and CuO5 pyramidal units, superconductivity from the Cu-O bi-layers apparently coexists with the weak ferromagnetic (WFM) order with magnetic ordering temperature T-m similar to 49 K. Low temperature anomalous in magnetic properties observed in both field-cooled (FC) and zero-field-cooled (ZFC) modes are closely related to the complex interplay and coexistence between weak ferromagnetic order and superconductivity as well as from structural distortion and sensitive sample oxygen concentration variation. No superconductivity or Ru-1212 structure can be detected for larger rare earth compounds R = La and Ce.