Pinning effects and critical currents in YBa 2Cu 3O 7− δ single crystals

Abstract

Magnetic measurements have been carried out on a series of four YBa 2Cu 3O 7− δ single crystals exhibiting different transition temperatures T c and a pronounced fishtail effect over a wide range of temperatures and in magnetic fields up to 11 T applied parallel to the c-axis. These crystals that originated from the same batch are prepared by solid-state reaction. The measured values of T c fall within the range of 65.5–92 K. Only the results on the highest and the lowest T c crystal are presented in this article. The lowest T c sample (65.5 K), called hereafter YBCO1, contains large green phase inclusions, with different orientations and the highest T c one (92 K), called hereafter YBCO2, has no green phase inclusions. The main idea of this work is to study the influence of these green phase inclusions on the pinning mechanisms. The analysis of our experimental data comes within the frame of the dynamic description based upon the theory of collective pinning. Our results show that the large green phase inclusions, with different orientations reduce the T c, the critical currents and the pinning in YBa 2Cu 3O 7− δ system. They act notably on their pinning mechanisms.