High trapped fields in bulk MgB2 prepared by hot-pressing of ball-milled precursor powder

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 B-0 = 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 B-0 = 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.