Magnetoresistance hysteresis and critical current density in granular (formula presented)

We report resistivity data on ceramic (formula presented) which is the first Cu-O based system in which superconductivity (SC) in the (formula presented) 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 (formula presented) superconducting materials. Below the superconducting transition (formula presented) the magnetoresistance (formula presented) is positive and unexpected hysteresis loops are observed. The hysteresis loop is completely different than that observed in conventional homogeneous superconductors. (formula presented) on decreasing the applied field (formula presented) is much smaller than the (formula presented) for increasing (formula presented) The width of the loops depends strongly on the weak-link properties. Similar hysteresis loops are observed in the reference nonmagnetic (formula presented) which is SC at (formula presented) thus the possibility that the hysteresis phenomenom is caused by the coexistence of both SC and magnetic states is excluded.