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S. Mohammad:
"Influence on non-superconducting additives on the pinning behaviour in MgB2 wires and bulk samples - a comparative study";
Betreuer/in(nen), Begutachter/in(nen): M. Reissner, P. Mohn; Festkörperphysik, 2008; Rigorosum: 02.04.2008.

The aim of this work was to study the influence of different additions on flux pinning behavior of MgB2 wires by investigation of the critical current density and magnetic relaxation. Wires with different concentration of SiC and with same concentration but different additives (SiC, B4C, Al2O3) were measured in a vibrating sample magnetometer. The results are compared with those obtained from bulk samples prepared without and with substitution of Al and SiC to study the effect of preparation process. The field and temperature dependence of the critical current density is analyzed in terms of different pinning models. From the time dependence of the magnetic moment, the mean effective activation energy, activation energy distributions and the current-energy relation were determined and interpreted in terms of collective pinning theory.
The analysis of pinning force strongly supports the grain boundary pinning as the main mechanism. From the temperature dependence of critical current density it is concluded that delta-l core pinning is most probable. The analysis of the relaxation measurements also favors 2D pinning.