| The study of superconductivity properties enhancement on MgB2 due to TaB2 doping at 2 and 5 at.% levels were carried out, in addition to the effect of atmospheric exposure on MgB 2. High energy ball milling was used for the purposes of fostering mechanical alloying, generation of nanometer sized particles, and strain inducements respectively. Atmospheric exposures at the University of Puerto Rico-Mayaguez and University of Wisconsin-Madison, revealed critical temperature of 37.5 K and 38 K based on resistivity measurements, while the lower critical field, Hc2 were 7.9 T and 7.0 T correspondingly. The formation of MgO during processing resulted in the variable grain connectivity and hence, the measured properties differences. SPEX 8000D processed materials revealed smaller particle size and higher strains in comparison to the Pulverisette-4 processed ones. The 5 at.% TaB2 doped MgB2 yielded the highest critical current density (Jc) corresponding to 474.1 kA/cm 2 at 2 T, while 344.4 kA/cm2 for SPEX 8000D and Pulverisette-4 materials. Correspondingly, the values of the flux pinning (Fp) deduced for the 5t.% TaB2 doped MgB2 processed with the SPEX-8000D mill was 7.58 GN/m3 while for same level of doping processed with the Pulverisette-4 processed material was 6.90 GN/m 3. The irreversibility field (Hirr) corresponding to the field associated with the maximization of the magnetization of the materials was 8.50 T for the 5 at.% doped MgB2, while for the same level of doping processed with Pulverisette-4 was 7.11 T. |
