Magnetic order and superconductivity in Eu_1.5 Ce_0.5RuSr₂Cu₂ O₁₀

AC magnetic susceptibility, x(T), and dc resistivity, p(T), measurements have been performed to study the superconductivity and magnetic properties of a polycrystalline Eu_1.5 Ce_0.5 RuSr₂Cu₂ O₁₀. X-ray diffraction shows that the single-phase compound crystallized into a tetragonal symmetry of space group I4/mmm. Ru spin ordering and superconductivity at 75 and 37 K, respectively, were evident in x(T). The magnetic responses associated with the Ru spin ordering were found to be strongly reduced by a weak applied field, indicating an antiferromagnetic character for the Ru moments. A two-step transition to the superconducting state was observed in p(T), where an intra-granular transition at T_C1=37 K and an inter-granular transition at T_C2=20 K were clearly seen. These observations confirm the coexistence of superconductivity and magnetic order at low temperatures.