Characterization and critical currents of the Superconducting ferromagnet RuSr/sub 2/GdCu/sub 2/O/sub 8/

Superconducting ferromagnet Ru/sub 1-x/Sr/sub 2/Gd Cu/sub 2+x/O/sub 8/ with x=0, 0.2 and 0.4 has been synthesized and characterized structurally, microstructurally and electrically by x-ray diffraction, scanning electron microscopy and resistivity measurements. Arrhenius plots of ln(/spl rho///spl rho//sub o/) vs T and potential energy are being reported. Two-different regimens of pinning are found. We show that U/sub 0/ data can be interpreted in terms of a possible structural change in the grain boundaries.