MgB 2 wire diameter reduction by hot isostatic pressing—a route for enhanced critical current density

The effect of wire diameter reduction on the critical current density of pristine MgB 2 wire was studied. Wires were treated by a hot isostatic pressing method at 570 °C and at pressures of up to 1.1 GPa. It was found that the wire diameter reduction induces an increase of up to 70% in the mass density of the superconducting cores. This feature leads to increases in critical current, critical current density, and pinning force density. The magnitude and field dependence of the critical current density are related to both grain connectivity and structural defects, which act as effective pinning centers. High field transport properties were obtained without doping of the MgB 2 phase. A critical current density j c of 3500 A mm −2 was reached at 4 K, 6 T for the best sample, which was a five-fold increase compared to MgB 2 samples synthesized at ambient pressure.