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Bulk superconducting MgB 2 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 MgB 2 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 10 6 A cm −2 at 15 K, indicating strong pinning due to nanocrystalline MgB 2 grains. Expected trapped field data for long trapped field magnets prepared from the available MgB 2 material are estimated.

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