Superconducting screening on different length scales in high-quality bulk MgB2 superconductor
J. Appl. Phys. 96, 4342 (2004); doi:10.1063/1.1790069
Issue Date: 15 October 2004
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High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ~1 µm, ~10 µm, and whole of the sample (~millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (
m). The analysis of the field dependence of
m for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to
m. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to
m in the intermediate fields (1 T<H<4 T at 20 K) and they can be used to obtain the value of Jc from critical state model, which corresponds to the transport Jc. The stretched exponential field dependence of these currents is similar to the one obtained for high-temperature superconductors, and it seems to be connected with the percolation of the currents.
©2004 American Institute of Physics
m). The analysis of the field dependence of
m for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to
m. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to
m in the intermediate fields (1 T<H<4 T at 20 K) and they can be used to obtain the value of Jc from critical state model, which corresponds to the transport Jc. The stretched exponential field dependence of these currents is similar to the one obtained for high-temperature superconductors, and it seems to be connected with the percolation of the currents.
©2004 American Institute of Physics
| History: | Received 8 March 2004; accepted 15 July 2004 |
| Permalink: |
http://link.aip.org/link/?JAPIAU/96/4342/1 |
KEYWORDS and PACS
magnesium compounds,
type II superconductors,
voids (solid),
crystal structure,
critical current density (superconductivity),
magnetic moments
- 74.70.Ad
Superconducting metals; alloys and binary compounds (including A15, MgB2, etc.) - 74.25.Ha
Magnetic properties of superconductors - 74.25.Fy
Transport properties of superconductors including electric and thermal conductivity, thermoelectric effects, etc - 74.25.Sv
Critical currents in superconductors - 61.72.Qq
Microscopic defects (voids, inclusions, etc.) - 61.66.Fn
Crystal structure of specific inorganic compounds - YEAR: 2004
RELATED DATABASES
PUBLICATION DATA
0021-8979 (print)
1089-7550 (online)
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