Possible Competition between superconductivity and magnetism in RuSr2Gd1.5Ce0.5Cu2O10-d (Ru-1222) Rutheno-cuprate compounds

The RuSr2Gd1.5Ce0.5Cu2O10-d (Ru-1222) compounds, with varying oxygen content, crystallize in a tetragonal crystal structure (space group I4/mmm). Resistance (R) versus temperature (T) measurements show that the air-annealed samples exhibit superconductivity with superconducting transition temperature (Tc) onset at around 32 K and R=0 at 3.5 K. On the other hand, the N2-annealed sample is semiconducting down to 2 K. Magneto-transport measurements on air-annealed sample in applied magnetic fields of 3 and 6 Tesla show a decrease in both Tc onset and TR=0. Magnetoresistance of up to 20% is observed in N2-annealed sample at 2 K and 3 T applied field. The DC magnetization data (M vs. T) reveal magnetic transitions (Tmag.) at 100 K and 106 K, respectively, for both air- and N2-annealed samples. Ferromagnetic components in the magnetization are observed for both samples at 5K and 20 K. The superconducting transition temperature (Tc) seems to compete with the magnetic transition temperature (Tmag.). Our results suggest that the magnetic ordering temperature (Tmag.) of Ru moments in RuO6 octahedra may have direct influence/connection with the appearance of superconductivity in Cu-O2 planes of Ru-1222 compounds. Key words: Ruthenocuprates, Superconductivity and Magnetism, Magneto transport and Magneto resistance. PACS: 74.25. Ha, 74.72. Jt, 75.25. +z, 75.30. Cr.