Magnetic field dependence of the relative critical current density in γ-irradiated polycrystalline YBa2Cu3O7

The effect of different doses of gamma-rays on the behavior of the critical current density, J(c) in an YBa2Cu3O7 polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a Co-60 gamma-ray source at a dose rate of 0.5 MR/h. J(c) was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J(c) above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non-monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by gamma-rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.