Invitada A. Serquis: Critical Currents, Creep and Vortex Pinning Energy in Bulk Carbon Nanotube-doped MgB2

A SERQUIS; G. SERRANO; G. PASQUINI; A. J. MORENO; B. EISMANN; L. CIVALE

Chicago

Conferencia; Applied Superconductivity Conference; 2008

Superconducting properties of polycrystalline MgB2 are modify by doping samples with Double wall (DW) carbon nanotubes (CNT). In previous works we have shown that the critical current density (Jc) and upper critical field (Hc2) are simultaneously enhanced for optimal doping contents (below 10%). To optimize Jc in MgB2 wires and tapes, it is necessary a deeper understanding of how doping affect their current carrying capability. The complete problem involves various aspects, from technical challenges to get to the bottom of the underlying basic physics.  In this work we investigate the pinning of vortices in doped and undoped polycrystalline MgB2 samples, which were prepared by solid-state reaction with 0-12.5%at nominal C content using DWCNT as the source of carbon. The critical temperature (Tc) decreased from 39 to 31K according to the doping content and the superconducting transitions were lower than 1K in all cases. By means of magnetization measurements, using a MPMS SQUID magnetometer, we studied the critical current density, normalized time relaxation rate S=dlnJ/dlnt and pinning energy in the various samples.  Complementary AC measurements were performed at high temperatures, close to Tc.  Correlations between the various results and the corresponding physical pictures are discussed.