We report a new method for synthesizing magnesium diboride (MgB 2) thin films which exhibit a steep increase in the slope of the upper critical field Hc2 versus decreasing temperature (i.e. |dH c2/dT|Tc|≈2.5 T K-1). An Hc2 of 38.4 T at 4.2 K and an extrapolated value of Hc2(0) above 43 T at 0 K are reported. Films of magnesium plus boron were deposited on unheated c-plane sapphire substrates by co-evaporation, and were subsequently annealed in a reducing atmosphere at temperatures below 600 °C. The use of a combination of a magnesium-rich stoichiometry (Mg/B>1/2) for the as-deposited film and a two-step annealing process was found to be critical in obtaining these high values of Hc2 and |dHc2/dT|Tc|.

Original languageEnglish (US)
Article number085009
JournalSuperconductor Science and Technology
Issue number8
StatePublished - Aug 1 2008

ASJC Scopus subject areas

  • Ceramics and Composites
  • Condensed Matter Physics
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry


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