Achievement of practical level critical current densities in Ba1−xKxFe2As2/Ag tapes by conventional cold mechanical deformation

The recently discovered iron-based superconductors are potential candidates for high-field magnet applications. However, the critical current densities (J(c)) of iron-based superconducting wires remain far below the level needed for practical applications. Here, we show that the transport Jc of Ba₁-xKxFe₂As₂/Ag tapes is significantly enhanced by the combination process of cold flat rolling and uniaxial pressing. At 4.2 K, Jc exceeds the practical level of 10(5) A/cm(2) in magnetic fields up to 6 T. The J(c)-H curve shows extremely small magnetic field dependence and maintains a high value of 8.6 × 10(4) A/cm(2) in 10 T. These are the highest values reported so far for iron-based superconducting wires. Hardness measurements and microstructure investigations reveal that the superior J(c) in our samples is due to the high core density, more textured grains, and a change in the microcrack structure. These results indicate that iron-based superconductors are very promising for high magnetic field applications.