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FIZIKA A 14 (2005) 1, 75 - 88
 
VORTEX PINNING AND CRITICAL CURRENTS IN NANOSTRUCTURED NOVEL
SUPERCONDUCTORS
IVICA KUŠEVIĆ and EMIL BABIĆ
Department of Physics, Faculty of Science, University of Zagreb,
HR-10000 Zagreb, Croatia
Received 28 September 2004; Accepted 13 June
2005
Online 7 November 2005
A systematic analysis of the parameters associated with vortex pinning in novel
superconductors containing nano-scale strong isotropic pinning centres (such as U/n
processed Bi2223/Ag tapes and nanoparticle added MgB2) has been carried out.
Although the systems studied are very different as regards their structures, types of
nano-scale defects and vortices, their pinning parameters (irreversibility fields and the
fields for the maximum volume pinning force) show distinct common features. In particular,
for moderate defect densities nf, in all these
systems the enhancement of the pinning parameters in nanostructured state is approximately
linear in nf over sizable field and temperature
windows. Accordingly, these systems exhibit a kind of matching effects with the effective
matching field Bf, correlated with the areal density
of defects. The field Bf forms a natural field scale
for the vortex pinning phenomena in such systems. However, at fields far from Bf, an interplay of different pinning mechanisms sets in. The
impact of these results for the future enhancement of the flux pinning and critical
currents in nanostructured Bi2223 and MgB2 superconductors is briefly
discussed.
PACS numbers: 74.60.Ge,74.60.Jg,74.62.Dh
UDC 538.945
Keywords: novel superconductors, vortex pinning, U/n processed Bi2223/Ag, MgB2
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