Flux pinning in Al doped TSMG YBCO bulk superconductors

The superconducting properties of Y1Ba2(Cu1−x Alx)3O7/Y2BaCuO5 bulk superconductors with different Al contents were studied (x = 0.0025–0.05). A peak effect was observed at intermediate magnetic fields over a wide temperature range below Tc. The influence of standard oxygenation (SO) at 400 ◦C and high pressure oxygenation (HPO) at 750 ◦C on the critical current density Jc was investigated. We show that the critical current density is higher by a factor of 3 in samples oxygenated at high pressure. The magnetization relaxation rates were investigated for an undoped HPO sample as well as for the lowest Al concentration for HPO and SO in the temperature range from 15 to 77 K and at magnetic fields of 0.5 and 1 T. The normalized relaxation rates, S, and the pinning potentials, U0, have been calculated from the time-dependent magnetization curves. (Some figures in this article are in colour only in the electronic version)