Dislocations as Origin of High Critical Current Density in Bulk MgB2

MgB
₂
is an important superconducting material that could be used as a basis of liquid-hydrogen renewable energy economy. The distinctive property of this material is its very high critical current density in bulk reaching 10
⁶
A/cm
²
. It is found that such a high critical current density is of nanoscale origin, and is linked to the pinning of magnetic flux quanta on grain boundaries. To advance this knowledge, a combination of atomic force microscopy, electron backscattered diffraction and SQUID magnetometry was used to clarify the exact dependence of critical current density on the density of dislocations in a cross-section of dense polycrystalline samples. It is found that in a system of randomly oriented grains, the dislocations residing in twist grain boundaries and their cross-points are responsible for the strong pinning in the material.