Flux mapping at 77 K and local measurement at lower temperature of thin-wall YBaCuO single-domain samples oxygenated under high pressure

• Published in: Physica. C, Superconductivity Superconductivity, 2009-10, Vol.469 (15), p.1200-1206
• Main Authors: Chaud, X., Noudem, J., Prikhna, T., Savchuk, Y., Haanappel, E., Diko, P., Zhang, C.P.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; High pressure; Magnetic properties; Oxygen annealing; Physics; Properties of type I and type II superconductors; Single domain; Superconductivity; Trapped field; Y-based cuprates
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2009.05.017

YBCO single-domain samples are suitable for the production of high trapped fields in the range 20–77 K using a cryocooler or liquid nitrogen. But the oxygenation process required to actually transform the single domains into superconductors induces an extensive crack network that is limiting the material performances. Thin-wall geometry has been introduced to reduce the diffusion paths and to enable a progressive oxygenation strategy. As a consequence cracks are drastically reduced. In addition the use of a high oxygen pressure (16 MPa) speeds up further the process by displacing the oxygen–temperature equilibrium towards the higher temperature of the phase diagram. The advantage of thin-wall geometry is that such an annealing can be applied directly to a much larger sample. Remarkable results are obtained without any doping by the combination of thin walls and oxygen high pressure. While classical plain samples yield 300–400 mT, a trapped field of 840 mT has been measured at 77 K on a 16 mm diameter Y123 thin-wall single-domain sample with an annealing time as short as 3 days. Local measurements with a fixed Hall probe on top of the sample were performed at lower temperature after magnetization either in a static field or in a pulse field. The trapped field is significantly higher at lower temperature. Cryocoolers become the key to compromise between performances and cryogenic cost around 40 K.