Magnetoresistance hysteresis and critical current density in granular RuSr2Gd2-xCexCu2O10-δ -: art. no. 134506

We report resistivity data on ceramic RuSr2Gd2-xCexCu2O10-delta which is the first Cu-O based system in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the Ru sublattice are considered to coexist. Due to the granular nature of the materials the critical current density at 5 K is extremely small as compared to other high-T-C superconducting materials. Below the superconducting transition (T-C), the magnetoresistance DeltaR(H)=R(H)-R(0) is positive and unexpected hysteresis loops are observed. The hysteresis loop is completely different than that observed in conventional homogeneous superconductors. DeltaR(H) on decreasing the applied field (H-ext) is much smaller than the DeltaR(H) for increasing (H-ext). The width of the loops depends strongly on the weak-link properties. Similar hysteresis loops are observed in the reference nonmagnetic NbSr2Gd1.5Ce0.5Cu2O10 which is SC at T-C=28 K, thus the possibility that the hysteresis phenomenom is caused by the coexistence of both SC and magnetic states is excluded.