Critical current density and irreversibility line of CuBa2Ca3Cu4Oy

The critical current density and irreversibility line of the single-phase polycrystalline sample of CuBa2Ca3Cu4Oy with Tc= 117 K have been estimated from measurements of magnetic hysteresis loops assuming Bean critical state model. Simple power law relations, Jc∝H-m, are observed in the magnetic field dependence of the intragrain Jc. Values of the intragrain Jc in a magnetic field of 1 T are about 106 and 104 A/cm2 at temperatures of 5 and 77 K, respectively. An exponential decay of the Jc with increasing temperature, Jc∝exp(-T/T0), is observed below 60 K. The characteristic temperature T0 of Cu-1234 is T0= 16.1 K in a magnetic field of 1.0 T. The dependence of the Jc on temperature is relatively small among the oxide superconductors. Simple power law relations, Jc∝(1-T/Tc)n, are found in whole ranges of the temperature and magnetic field. The value of n is 5.24 for a magnetic field of 1.0 T. The irreversibility fields at 70 and 77 K are estimated to be 9.5 and 3.7 T, respectively. The temperature dependence of the Hirr is fitted by Hirr=a(1-T/Tc)n with a=2130 and n=5.91