Flux pinning in neutron irradiated YBa2Cu3O7-x

This paper reports on identical polycrystalline samples of YBa2Cu3O7-x irradiated with fast neutrons (E > 0.1 MeV) in eight steps between 0 and 2.1 x 1018 n/cm2. Notable irradiation effects include a Tc depression of nearly 2 K at the highest fluence and large improvement in the critical current density for fields from 0-9 T and temperatures between 4-80 K. Critical currents approaching 2 x 107 A/cm2 are observed for optimally irradiated materials at 5K (in zero field) while at 77 K, Jc (O kOe) approaches 5 x 105 A/cm2. Irradiation is seen to take a nearly equilibrium magnetization curve at 77 K and broaden it to a significantly hysteretic curve. A substantial shift in the effective pinning potential as a function of current density is inferred from magnetic relaxation measurements at H = 1T. This is the first such measurement in which systematically increased activation energies for flux creep (as a function of current density) are noted