High trapped fields in bulk MgB₂prepared by hot-pressing of ball-milled precursor powder

Abstract

Bulk superconducting MgB2 samples, 20?mm in diameter, were prepared by hot-pressing of ball-milled Mg and B powders using fine-grained boron powders. High maximum trapped fields of B0?=?5.4?T were obtained at 12?K in one of the investigated trapped field magnets (height 8?mm) at the centre of the bulk surface. Investigating the temperature dependence of the trapped field for short MgB2 samples (height ?1.6?mm), trapped fields of up to B0?=?3.2?T at 15?K were achieved. These high trapped fields are related to extremely high critical current densities of up to 106?A?cm?2 at 15?K, indicating strong pinning due to nanocrystalline MgB2 grains. Expected trapped field data for long trapped field magnets prepared from the available MgB2 material are estimated.