Possible competition between superconductivity and magnetism in RuSr₂Gd_1.5Ce_0.5Cu₂O_10-δ ruthenocuprate compounds

Abstract

The RuSr₂Gd_1.5Ce_0.5Cu₂O_10-δ (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 superconduting transition temperature (T_c) 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 an air-annealed sample in applied magnetic fields of 3 and 6 T (Tesla) show a decrease in both T_c onset and T_R=0. Magnetoresistance of up to 20% is observed in the N₂-annealed sample at 2 K and 3 T applied field. The dc magnetization data (M vs T) reveal magnetic transitions (T_mag) 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 5 K and 20 K. The superconducting transition temperature (T_c) seems to compete with the magnetic transition temperature (T_mag). Our results suggest that the magnetic ordering temperature (T_mag) of Ru moments in RuO₆ octahedra may have direct influence/connection with the appearance of superconductivity in Cu-O₂ planes of Ru-1222 compounds.