Superconductivity of individual grains and inter-grain boundaries for polycrystalline FeSr2YCu2O6+yFeSr2YCu2O6+y

Polycrystalline FeSr2YCu2O6+yFeSr2YCu2O6+y was synthesized and its transport and magnetic properties were studied. Diamagnetism was observed below 60 K. Zero resistivity was observed below 38 K under zero magnetic field and below 10 K under 160 kOe. A two-step transition was observed in resistivity measurement due to the superconductivity in individual grains and across inter-grain boundaries. The critical current density in individual grains, Jcintra, at 2 K under 1 kOe was deduced 3.4 × 105 A/cm2 from the Bean model. In contrast, the critical current density in inter-grain boundaries, Jcinter, at 2 K was 1.7 A/cm2 in voltage–current measurement. The two-step transition seems to result from the large difference between Jcintra and Jcinter.