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Effect of sample size on magnetic Jc for MgB2 superconductor

Appl. Phys. Lett. 84, 3109 (2004); doi:10.1063/1.1713031

Issue Date: 19 April 2004

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J. Horvat, S. Soltanian, X. L. Wang, and S. X. Dou
Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522, Australia
A strong effect of sample size on magnetic Jc(H) was observed for bulk MgB2 when Jc is obtained directly from the critical state model. Thus obtained zero-field Jc (Jc0) decreases strongly with the sample size, attaining a constant value for the samples larger than a few millimeters. On the other hand, the irreversibility field (Hirr) defined at Jc = 100 A/cm2 increases with the sample size. The decrease of Jc0 is described in terms of voids in the bulk MgB2 samples and superconducting screening around the cells of superconducting material between these voids (35 µm), because of concentration of the current in the narrow bridges connecting the cells. For samples larger than a few millimeters, the value of magnetic Jc is in agreement with the transport Jc and it is restricted by the voids. The critical state model is not suitable for obtaining Jc for small bulk MgB2. The increase of Hirr with the sample size is an artifact of defining Hirr by the value of Jc at which an additional superconducting screening on 1 µm scale dominates Deltam. ©2004 American Institute of Physics.
History: Received 16 September 2003; accepted 26 February 2004
Permalink: http://link.aip.org/link/?APPLAB/84/3109/1
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KEYWORDS and PACS

Keywords
PACS
  • 74.25.Sv
    Critical currents in superconductors
  • 74.70.Ad
    Superconducting metals; alloys and binary compounds (including A15, MgB2, etc.)
  • YEAR: 2004

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ISSN:
0003-6951 (print)   1077-3118 (online)
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REFERENCES (13)
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  12. In addition to the restriction of Jcs in the bridges, the values of Jcc and Jcs also depend on the redistribution of the currents in the cells. This occurs because Jcc is either added to, or subtracted from Jcs, depending on the position in the cell (Fig. 5).
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