Critical current density and flux pinning in superconducting MgB2

One of the most important factors which determine the critical Current density in superconducting MgB2 bulks and wires is the electrical connectivity and this can be improved by making the packing density of the superconductor high and by reducing the insulating oxide layers. In this study the flux pinning strength, which is another important factor. is investigated in detail. It is empirically known that the critical current density is proportional to the flux pinning force of grain boundaries and to the reciprocal size of MgB2 grains. The flux pinning force of grain boundaries is estimated using the theoretical result of Yetter et al. for the electron scattering mechanism using the impurity parameter estimated from the residual resistivity of superconducting grains. The obtained result with the observed grain size approximately explains the experimental result and shows that the flux pinning by grain boundaries is dominant in MgB2. The potential for the high critical current density of MgB2 is discussed by comparing with that of Nb3Sn. (c) 2008 Elsevier B.V. All rights reserved.