Transition from columnar to point pinning in coated conductors: critical currents that are independent of magnetic field direction
We identify a sharp crossover in the vortex pinning of a high-temperature superconductor with nanocolumnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field BX(T) the vortex response is no longer determined by the nanocolumns, and is instead det...
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Veröffentlicht in: | Superconductor science & technology 2012-07, Vol.25 (7), p.75009-1-5 |
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Sprache: | eng |
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Zusammenfassung: | We identify a sharp crossover in the vortex pinning of a high-temperature superconductor with nanocolumnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field BX(T) the vortex response is no longer determined by the nanocolumns, and is instead determined by point-like pinning. This crossover is evident as a change in the dependence of the critical current density on the angle between the applied magnetic field and the nanocolumns. It also leads to the field-orientation-independent power law index n of the E-J curves. Below the transition, there is a strong maximum in JC when the field is aligned parallel to the columns and n depends on field direction. Above the transition, n is independent of the field direction and there is a JC minimum for H parallel to the columns. We discuss a possible mechanism for such behavior change, as well as testing and confirming a prediction that the crossover must become very broad at high temperatures and low fields. |
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ISSN: | 0953-2048 1361-6668 |
DOI: | 10.1088/0953-2048/25/7/075009 |