Expulsion of magnetic flux in a type-I superconducting strip

Jung, G.; Girard, T.A.; Valko, Pavol; Gomes, M. L.; Jeudy, V.; Limagne, D.; Waysand, G.

doi:10.1016/s0921-4534(01)01126-1

Cited by 16 publications

(11 citation statements)

References 27 publications

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“…The results generally confirm H c3 as the first flux expulsion field, and suggest the existence of a barrier to the expulsion of flux. The measured critical fields themselves moreover yield determinations of the Ginzburg-Landau parameter κ(T c ) for the materials in agreement with those obtained from measurements on superconducting spheres, and a factor ∼ 2 below those derived from the more accepted magnetization measurements on thin films/foils (which agree with BCS estimates).The fast pulse measurement technique has been described in detail elsewhere [9,12,13]. The samples were cut from 98.8 − 99.999% pure, annealed, pinholefree metallic foils of 10-125 µm thicknesses (d).…”

supporting

confidence: 75%

“…This description however fails to treat the general nucleation of the superconductive state during a continuous decrease of the applied field. Neither does it include the effects of short-or long-range interactions, nor effects associated with demagnetization or surface nucleation.Recent experiments on a tin foil in a continuously decreasing applied field using a fast-pulse induction technique observed the first expulsion of magnetic flux to occur at H c3 [9], which the authors then discounted as coincidental. We here report an examination of the superconductive transition of several type-I materials, listed in Table 1, at several temperatures in a gradually decreasing magnetic field using fast-pulse techniques.…”

mentioning

confidence: 99%

“…Recent experiments on a tin foil in a continuously decreasing applied field using a fast-pulse induction technique observed the first expulsion of magnetic flux to occur at H c3 [9], which the authors then discounted as coincidental. We here report an examination of the superconductive transition of several type-I materials, listed in Table 1, at several temperatures in a gradually decreasing magnetic field using fast-pulse techniques.…”

mentioning

confidence: 99%

“…The fast pulse measurement technique has been described in detail elsewhere [9,12,13]. The samples were cut from 98.8 − 99.999% pure, annealed, pinholefree metallic foils of 10-125 µm thicknesses (d).…”

mentioning

confidence: 99%

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Nucleation of superconductivity in thin type-I foils

2007

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The expulsion of flux in five type-I materials in a slow, continuously decreasing perpendicular magnetic field provides evidence for the possible existence of a barrier in the superconductive transition. The variation of the observed critical fields with temperature yields Ginzburg-Landau parameter determinations for the materials which suggests the behavior of the study materials to be more strongly type-I than generally considered.PACS numbers: 74.55. + h, 74.25.N fThe magnetic cycling of a type-I superconductor is fundamentally hysteretic [1,2]: the first order transition permits superheating and supercooling states. For thin flat samples in a perpendicular field, the hysteresis is even more pronounced because of a demagnetizationgenerated, geometrical edge barrier [3] which inhibits the penetration of flux in increasing field. A topological hysteresis in the intermediate state flux structures is also observed between crossing the phase line in increasing or decreasing field [4].It is commonly assumed that no similar barrier exists in decreasing field [5,6], and that the expulsion of flux is governed by the basic tenets of phase transitions. In the nucleation regime (H a > H c2 ), only seeds of the superconductive phase with size larger than a critical radius evolve; smaller seeds collapse [7,8]. In the spinodal regime (H a ≤ H c2 ), there is no free energy barrier to nucleation of the superconducting phase and arbitrarily small seeds may evolve. This description however fails to treat the general nucleation of the superconductive state during a continuous decrease of the applied field. Neither does it include the effects of short-or long-range interactions, nor effects associated with demagnetization or surface nucleation.Recent experiments on a tin foil in a continuously decreasing applied field using a fast-pulse induction technique observed the first expulsion of magnetic flux to occur at H c3 [9], which the authors then discounted as coincidental. We here report an examination of the superconductive transition of several type-I materials, listed in Table 1, at several temperatures in a gradually decreasing magnetic field using fast-pulse techniques. The results generally confirm H c3 as the first flux expulsion field, and suggest the existence of a barrier to the expulsion of flux. The measured critical fields themselves moreover yield determinations of the Ginzburg-Landau parameter κ(T c ) for the materials in agreement with those obtained from measurements on superconducting spheres, and a factor ∼ 2 below those derived from the more accepted magnetization measurements on thin films/foils (which agree with BCS estimates).The fast pulse measurement technique has been described in detail elsewhere [9,12,13]. The samples were cut from 98.8 − 99.999% pure, annealed, pinholefree metallic foils of 10-125 µm thicknesses (d). Each foil was placed within a rectangular copper pickup loop of 800 µm width, in contrast to Ref.[9] where the tin strip was electroplated on only one loop branch. The loop is transformer...

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supporting

confidence: 75%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Nucleation of superconductivity in thin type-I foils

2007

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“…Some unreacted Mg was found in the wire samples, and unreacted Mg can significantly affect the resistivity. 17,18 The difference between the superconducting properties of the normal MgB 2 and the excess Mg wire samples can be estimated according to our results and those of Refs. 17 and 18.…”

Section: Resultsmentioning

confidence: 64%

Excess Mg addition MgB2/Fe wires with enhanced critical current density

Zeng

Lü

et al. 2008

Journal of Applied Physics

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MgB 2 /Fe wires with 10 at. % excess Mg produced by in situ powder-in-tube processing werecompared to normal stoichiometric MgB 2 /Fe wires prepared by the same method. It was found thatthe critical current density J c and the irreversibility field (H irr) were significantly enhanced forMgB 2 /Fe wires with excess Mg. The transport J c for 10 at. % Mg excess samples sintered at 800 degrees C, measured at a field of up to 14 T, increased by a factor of 2 compared to that for the normal MgB 2 wires. The best J c results for the 10 at. % Mg excess sample were obtained by heating thesample at 600 degrees C for 1 h; the J c at a field of 8 T and at temperature of 10 K reached 3104 A/cm2. The detailed analysis of the effect of excess Mg on the microstructures, the J c , andthe H irr , of MgB 2 /Fe wires are presented in this paper.

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