Magnetic-flux penetration in Li doped and undoped Bi2Sr2CaCu2Oz cast tapes before and after fast-neutron irradiation

In a study of the effects of Li fission on magnetic-flux pinning in Bi2Sr2CaCu2Oz (2212), a high-resolution, magneto-optical imaging technique (MOT) has been employed to conduct the first direct observations of microscopic flux flow in Li doped and undoped 2212 polycrystalline tapes before and after fast-neutron irradiation. The studies were performed at applied magnetic fields in the range of 0 to +/-65 mT and at temperatures of 20, 30 and 40 K. The local magnetization behavior was correlated with bulk magnetization measurements obtained by superconducting quantum interference device (SQUID) magnetometry at the same applied fields and temperatures. The MOT studies showed that flux penetration in both the Li doped and undoped tapes was highly non-uniform. Measurements by the two techniques demonstrated that the neutron-irradiation treatment caused a significant increase in the magnetic-flux pinning in both tapes. SQUID measurements performed at applied fields up to +/-5 T showed that the irradiation treatment increased pinning by the same factor (2.2 at 20 K and 30 K) in the two tapes.