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High critical currents in iron-clad superconducting MgB2 wires


Technically useful bulk superconductors must have high transport critical current densities, Jc, at operating temperatures. They also require a normal metal cladding to provide parallel electrical conduction, thermal stabilization, and mechanical protection of the generally brittle superconductor cores. The recent discovery of superconductivity at 39 K in magnesium diboride (MgB2)1 presents a new possibility for significant bulk applications2,3,4,5, but many critical issues relevant for practical wires remain unresolved. In particular, MgB2 is mechanically hard and brittle and therefore not amenable to drawing into the desired fine-wire geometry. Even the synthesis of moderately dense, bulk MgB2 attaining 39 K superconductivity is a challenge because of the volatility and reactivity of magnesium. Here we report the successful fabrication of dense, metal-clad superconducting MgB2 wires, and demonstrate a transport Jc in excess of 85,000 A cm-2 at 4.2 K. Our iron-clad fabrication technique takes place at ambient pressure, yet produces dense MgB2 with little loss of stoichiometry. While searching for a suitable cladding material, we found that other materials dramatically reduced the critical current, showing that although MgB2 itself does not show the ‘weak-link’ effect characteristic of the high-Tc superconductors, contamination does result in weak-link-like behaviour.

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Figure 1: The MgB2 ribbons were fabricated using Fe or Cu/Fe tubes with outside diameters of 5–6.35 mm.
Figure 2: MH curves for sintered iron-clad MgB2.
Figure 3: Jc(magnetization) versus H plots for various MgB2 samples.
Figure 4: Effect of metal additions on the superconducting properties of MgB2.


  1. 1

    Nagamatsu, J. et al. Superconductivity at 39 K in magnesium diboride. Nature 410, 63–64 (2001).

    ADS  CAS  Article  Google Scholar 

  2. 2

    Larbalestier, D. C. et al. Strongly linked current flow in polycrystalline forms of the superconductor MgB2. Nature 410, 186–189 (2001).

    ADS  CAS  Article  Google Scholar 

  3. 3

    Finnemore, D. K. et al. Thermodynamic and transport properties of superconducting Mg10B2. Phys. Rev. Lett. 86, 2420–2422 (2001).

    ADS  CAS  Article  Google Scholar 

  4. 4

    Canfield, P. C. et al. Superconductivity in dense MgB2 wire. Phys. Rev. Lett. 86, 2423–2426 (2001).

    ADS  CAS  Article  Google Scholar 

  5. 5

    Eom, C. B. et al. High critical current density and enhanced irreversibility field in superconducting MgB2 thin films. Nature 411, 558–560 (2001).

    ADS  CAS  Article  Google Scholar 

  6. 6

    Jin, S. et al. High Tc superconductors—composite wire fabrication. Appl. Phys. Lett. 51, 203 (1987).

    ADS  CAS  Article  Google Scholar 

  7. 7

    Sumption, M. D. et al. Transport current in MgB2 based superconducting strand at 4.2 K and self-field. Preprint cond-mat/0102441 at 〈〉 (2001).

  8. 8

    Grasso, G. et al. Large transport critical currents in unsintered MgB2 superconducting tapes. Preprint cond-mat/0103563 at 〈〉 (2001).

  9. 9

    Glowacki, B. A. et al. Superconductivity of powder-in-tube MgB2 wire. Supercond. Sci. Technol. 14, 193–199 (2001).

    ADS  CAS  Article  Google Scholar 

  10. 10

    Masalski, T. (ed.) Binary Phase Diagrams. 46, 1,434 2nd edn (ASM International, Metals Park, OH, 1990).

    Google Scholar 

  11. 11

    Slusky, J. S. et al. Loss of superconductivity with the addition of Al to MgB2 and a structural transition in Mg1-xAlxB2. Nature 410, 343–345 (2001).

    ADS  CAS  Article  Google Scholar 

  12. 12

    Jin, S. et al. High critical currents in Y-Ba-Cu-O superconductors. Appl. Phys. Lett. 52, 2074–2076 (1988).

    ADS  CAS  Article  Google Scholar 

  13. 13

    Tinkham, M. Introduction to Superconductivity 185 (McGraw-Hill, New York, 1975).

    Google Scholar 

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Correspondence to S. Jin.

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Jin, S., Mavoori, H., Bower, C. et al. High critical currents in iron-clad superconducting MgB2 wires. Nature 411, 563–565 (2001).

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