Study of the pinning behaviour in yttrium-doped Eu-123 superconductors

The magnetic properties of a series of superconductors (Eu1-xYx)Ba2Cu3O7-y (x = 0, 0.2, 0.3, 0.5, 0.7 and 0.8) have been investigated by magnetic meas urements from 20 to 90 K. Magnetization hysteresis loops of the Y-doped sam ple exhibit a strongly developed second peak in the higher temperature rang e. We discuss the experimental results in the framework of a stress-field p inning model. The stress field induced by the lattice mismatch is also an e ffective pinning centre, in addition to pinning by 211 phase precipitates a nd oxygen vacancies. We further suggest that in the (Eu1-xYx)Ba2Cu3O7-y sam ples the oxygen deficient regions induced by the stress held in Cu-O chains also act as pinning centres, thus causing the second peak in the J(c)-B cu rves of (Eu1-xYx)Ba2Cu3O7-y.