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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 measurements from 20 to 90 K. Magnetization hysteresis loops of the Y-doped sample exhibit a strongly developed second peak in the higher temperature range. We discuss the experimental results in the framework of a stress-field pinning model. The stress field induced by the lattice mismatch is also an effective pinning centre, in addition to pinning by 211 phase precipitates and oxygen vacancies. We further suggest that in the (Eu1-xYx)Ba2Cu3O7-y samples the oxygen deficient regions induced by the stress field in Cu-O chains also act as pinning centres, thus causing the second peak in the Jc-B curves of (Eu1-xYx)Ba2Cu3O7-y.