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

摘要

Nanocrystalline superconducting MgB_2 bulks were prepared by high pressure sintering of ball milled MgB_2 powders. A significant improvement in the in-field critical current density J_c has been obtained in the bulk sintered at 700 °C. The value of J_c reaches as high as 10~5 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 J_c.