Magnetoresistance hysteresis and critical current density in granularRuSr2Gd2−xCexCu2O10−δ

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We report resistivity data on ceramic RuSr 2 Gd 2 - x Ce x Cu 2 O 1 0 - δ which is the first Cu-O based system in which superconductivity (SC) in the CuO 2 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 ΔR(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. ΔR(H) on decreasing the applied field (H e x t ) is much smaller than the ΔR(H) for increasing (H e x t ). The width of the loops depends strongly on the weak-link properties. Similar hysteresis loops are observed in the reference nonmagnetic NbSr 2 Gd 1 . 5 Ce 0 . 5 Cu 2 O 1 0 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.