Dresden 2003 – scientific programme

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TT: Tiefe Temperaturen

TT 5: Supraleitung: Massivmaterialien, Bandleiter, Pinning, Vortexdynamik, Transporteigenschaften, Korngrenzen I

TT 5.7: Talk

Monday, March 24, 2003, 16:15–16:30, HSZ304

Improved pinning properties of nanocrystalline bulk MgB₂ and of MgB₂ tapes — •Günter Fuchs, Karl-Hartmut Müller, Stefan-Ludwig Drechsler, Sergej Shulga, Konstantin Nenkov, Nadejda Kozlova, Yurij Skourski, Helge Rosner, Jürgen Eckert, Olaf Perner, Andreas Gümbel, Wolfgang Hässler, Claus Fischer, and Ludwig Schultz — Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, PO Box 270116, D-01171 Dresden, Germany

The properties of nanocrystalline MgB₂ bulk superconductors prepared by mechanical alloying of Mg and B powders and a following hot compaction were investigated by resistance and magnetization measurements. High critical current densities of 7× 10⁵A/cm² at 10 K and irreversibility fields up to about 17 T were found. The improved pinning of this nanocrystalline material is attributed to the large number of grain boundaries. The upper critical field H_c2 obtained from dc field and pulsed field measurements was found to increase up to 23 T at zero temperature. The H_c2(T) data are strongly related to the electronic structure of MgB₂ and can be described in the framework of a two-band model using two groups of quasiparticles with different Fermi velocities corresponding to different sheets of the Fermi surface. The nanocrystalline MgB₂ was used as starting material for tapes prepared by the ’powder in tube’ technique. The superconducting properties of these tapes are presented.