Saturday, 3G-07, 12:15-12:20

Magnetic Pinning in YBCO

S. C. Wimbush

J. H. Durrell, M. G. Blamire, R. B. Dinner, S. L. Sahonta, S. A. Harrington, R. Bali and J. L. MacManus-Driscoll

Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK. Tel.: +44 1223 767140 Fax: +44 1223 334567 Email: scw42@cam.ac.uk

The practical introduction of effective flux pinning sites into high-temperature superconductors is of paramount importance for their eventual widespread application. The search for suitable processes for the generation of nanoscale defects to act as core pinning sites in the superconductor matrix has been extensive and highly fruitful, yielding improvements in the critical current density under specific experimental conditions approaching an order of magnitude. At the same time, many fundamental experiments have been performed on the formation of magnetic pinning sites in both low and high temperature superconductors, and their influence on the vortex lattice. However, to date no practical and effective approach to the formation of magnetic pinning centres for critical current enhancement in the high-temperature materials has been proposed.

We demonstrate the successful incorporation of nanoscale ferromagnetic pinning centres within YBCO thin films. For sufficiently low dopant concentrations, the suppression of transition temperature due to poisoning of the YBCO is overcome. Even at these low dopant levels, the resultant films exhibit a coexistence of superconductivity and ferromagnetism, and a consequent absolute enhancement of the critical current density up to a factor two under all applied fields and field orientations, including self field. The nature of the pinning is investigated, and a theoretical framework for the observed behaviour postulated. The potential for future development is outlined and discussed.

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