High intergranular critical currents in metallic MgB2 superconductor

Strong evidence for high intergranular critical current densities and large bulk magnetic flux pinning in superconducting polycrystalline MgB2 has been observed. The presence of strongly-coupled grain boundaries in this material has been confirmed by a dramatic collapse of the magnetic hysteresis loop when a bulk specimen is ground into a fine powder and re-measured under similar conditions. Further evidence for strong intergrain links in polycrystalline MgB2 is provided by the continuous variation of the remanent magnetic moment up to the full penetration field of a bulk sample. The absence of weak-link nature in this material has profound implications for its potential in a wide range of engineering applications.