E-J characteristics and n value of melt-textured REBa/sub 2/Cu/sub 3/O/sub x/ (RE: Nd, Y)

Melt-textured NdBa/sub 2/Cu/sub 3/O/sub x/ (Nd123) exhibits the secondary peak effect on the magnetic field dependence of the critical current density (J/sub c/), which is attributed to the field-induced pinning. The electric field (E)-the current density (J) characteristics will be affected by the field-induced pinning. With the aim of clarifying this effect, we have investigated the E-J characteristics for melt-textured Nd123 with the secondary peak and YBa/sub 2/Cu/sub 3/O/sub x/ (Y123) with smaller secondary peak through dc magnetization and ac susceptibility. The n value was estimated on the assumption that E follows the power law: E=E/sub c/(J/J/sub c/)/sup n/. The n value was about 30 at 77 K for Y123. In the case of Nd123, the peak structure was observed on the magnetic field dependence of the n value, which exceeded 60 at 77 K. This suggests that the n value is increased by the field-induced pinning.