Flux pinning and flux creep in uranium-doped (Bi, Pb)-Sr-Ca-Cu-O superconducting powders after thermal-neutron irradiation

Fission fragment damage was introduced into uranium-doped powdered Bi_1.7Pb_0.3Sr₂Ca₂Cu₃ O_y by irradiation with thermal neutrons. Measurements of magnetic hysteresis and flux creep were made using a vibrating sample magnetometer. Magnetic hysteresis and intragranular critical current densities, obtained from the magnetic hysteresis using the critical state model, show an increase upon irradiation of a factor of 70 at 50 K and 0.8 T. Flux creep data, interpreted as nonlinear relations between pinning energy and magnetization, as temperature-dependent pinning energies, or as distributions of pinning energies, show significant increases in pinning energy upon irradiation. The irreversibility line is found to shift to higher magnetic fields upon irradiation. It is concluded that the increase in flux creep and decrease in critical current density at higher temperatures appear to limit the potential utility of this family of oxide superconductors to the lower-temperature regime