Abstract
MgB2 bulk samples were prepared using high‐energy ball milling in nitrogen atmosphere followed by cold isostatic pressing and hot isostatic pressing to increase densification and grain connectivity. Higher values of critical current densities Jc at high magnetic fields could be obtained after milling than those obtained with unmilled bulk samples. Jc values around 20,000 A/cm2 at 7 T, 4.2 K were found for the MgB2 sample milled for 300 minutes compared to 1000 A/cm2 for the unmilled material. The milling increased electron scattering and resistivity, increasing the irreversibility field μ0Hirr of the samples. The milled samples showed higher values of μ0Hirr than the unmilled sample. However, the milled samples showed lower pinning strength than the unmilled sample as a result of their larger average grain size after HIP, in spite of their higher μ0Hirr.
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