Sintering process and critical current density of low activation Mg11B2 superconductors from low temperature to high temperature

• Both Hirr and Jc of our low activation Mg11B2 bulks are better than previous studies.
• Low-temperature sintering leads to better Jc at high field, worse Jc at low field.
• The highest Jc value (2.2 ×105 A cm−2) was achieved in low activation Mg11B2 bulks.

As the “low activation” superconductor, Mg11B2 has a potential application in superconducting coils for fusion reactor. In present work, the sintering process and critical current density of low activation Mg11B2 superconductors were systemically studied from low temperature to high temperature. It was found that the Jc and Hirr values of Mg11B2 bulks in present work are both obviously higher than that of those samples prepared in previous studies. Furthermore, the low-temperature sintered samples exhibit better Jc performance at high fields than the high-temperature sintered samples, due to strong grain boundaries pinning. On the other hand, the high-temperature sintered samples have higher Jc at low fields compared to low-temperature sintered samples, mainly owing to their better crystallinity and grain connectivity. The highest Jc value (2.20 ×105 A cm−2 at 20 K, self-field) is obtained in the Mg11B2 sample sintered at 850 °C for 45 min.