Possible competition between superconductivity and magnetism in RuSr<SUB>2</SUB>Gd<SUB>1.5</SUB>Ce<SUB>0.5</SUB>Cu<SUB>2</SUB>O<SUB>10-&#948;</SUB> ruthenocuprate compounds

The RuSr2Gd1.5Ce0.5Cu2O10-&#948; (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 (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 an air-annealed sample in applied magnetic fields of 3 and 6 T (Tesla) show a decrease in both Tc onset and TR=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 (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 5 K 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

Systematic induction of superconductivity in the Cu (Y1−xCax)Ba2Cu2O6+δ (\delta \approx 0.3 ) system by Ca substitution

Series of samples of the composition Cu (Y1−xCax)Ba2Cu3O6+δ () have been prepared by a solid-state synthesis route. Precise oxygen content was determined for all the samples by iodometric titration. The c lattice parameter increases with increasing x, indicating successful substitution of Y3+ by the bigger Ca2+ ion. Resistivity (R) versus temperature (T) measurements show that the pristine sample (x = 0.0) is semiconducting down to 5 K. Induction of superconductivity is seen with increasing x. The x = 0.10 sample exhibits the onset of superconducting transition (Tconset) at 42 K without attaining a zero resistance superconducting transition temperature (TcR = 0) state above 5 K. For the x = 0.15 and 0.20 samples TcR = 0 is observed at 25 and 35 K with Tconset at 52 and 61 K, respectively. DC magnetic susceptibility measurements corroborated the findings from the resistivity measurements. Thermoelectric power (S) measurements in the temperature range of 5–300 K exhibit TcS = 0 at 25 and 35 K respectively for x = 0.15 and 0.20 samples. The room-temperature S value decreases with increasing x, indicating an enhanced number of mobile holes. Magneto-transport measurements in applied magnetic fields of 3 and 6 T show a broadening of the superconducting transition. These results will be useful in constructing a more complete phase diagram of the Cu (Y1−xCax)Ba2Cu3O6+δ system in terms of x and δ