Effect of polymers doping on flux pinning behavior of MgB2

The effects of polymers doping on irreversibility field (Hirr) and critical current density (Jc) of MgB2 have been investigated in this work. It is found that both Jc, and Hirr, are improved by doping at relative lower temperature region. The Jc−B curves of all samples studied in this work are well fitted using Jc(B) formula in percolation model. The values of upper critical field anisotropy (γ) are obtained from the fitting result at various temperatures. It is observed that values of γ for polymers doping samples are reduced at these temperatures. This is considered to be responsible for the enhancement of values of Jc for doped samples. Moreover, the percolation threshold, pc, is found to be enhanced with increasing temperature. It is believed that the grain boundary pinning is still dominating in MgB2, while the deviation of experimental data from the theoretical values is due to the percolation of suppercurrent in polycrystalline MgB2.