Disordered nanocrystalline superconducting magnesium diboride: A significant improvement in in-field critical current density

Nanocrystalline superconducting MgB2 bulks were prepared by high pressure sintering of ball milled MgB2 powders. A significant improvement in the in-field critical current density Jc has been obtained in the bulk sintered at 700 °C. The value of Jc reaches as high as 105 A cm−2 at 5 K, 8 T and 104 A cm−2 at 15 K, 6 T. Intragranular defects and a large number of grain boundaries acting as pinning centers are both responsible for the higher Jc.