STUDIES ON MAGNETIZATION AND MICROWAVE PROPERTIES OF GAMMA-RAY-IRRADIATED SM-BA-CU-O SUPERCONDUCTORS

Studies on the effect of gamma-ray irradiation on critical transition temperature, transport and magnetic critical current density (at 4.2 K ), high-field magnetization (at 4.2 K), and microwave-induced d.c. vol tage (inverse a.c. Josephson effect) have been performed on SmBa2Cu3O7 -delta ceramic superconducting samples prepared by the coprecipitation technique. Gamma-ray irradiation of the samples was carried out using a Co-60 source of 10(3) Ci strength for several hundreds of hours; th e dose received by the samples was 80 K rad/h. Gamma-Ray irradiation w as found to have no effect on its structural modification and on the c ritical transition temperature. However, transport and magnetic critic al current density are increased. Irradiation also caused a significan t increase in the high-field magnetic hysteresis, which is presumably connected with the creation of radiation-induced mobile defects. An ap preciable decrease in the microwave-induced d.c. voltage at 77 K was a lso observed after irradiation, which suggests that the mobile defects are clustered at the major defect region and thus reduce the total nu mber of weak links. Enhancement of transport and magnetic critical cur rent density may be due to the stronger pinning of flux lines at the g amma-ray-induced defect site in SBCO ceramic superconductors.