By using three types of MgB 2 superconductors, such as c-axis-oriented single-crystal films, c-axis-oriented columnar-structure films and films without c-axis orientation perpendicular to the substrate surface, we have investigated the intrinsic pinning effect in MgB 2 superconductors. The strong field performance of J c was observed by turning the orientation of grains from the c axis to the a axis. No c-axis-oriented MgB 2 films showed a noticeable increase of J c at high fields compared with c-axis-oriented films, whether they had columnar structures or not. Our results clearly show that MgB 2 has strong intrinsic pinning caused by the large anisotropy of the superconducting energy gap in the boron layers like high-T c cuprate superconductors with a layered structure.

We have successfully fabricated c-axis-oriented MgB2 thin films by using a laser-assisted chemical vapor deposition (LACVD) technique. Mg and B sources were supplied by pulsed laser ablation and a mixture of B2H6 gas in H2, respectively. The MgB2 thin films grown on Al2O3(0001) substrates at 400 °C showed a superconducting transition temperature of 40.2 K with a sharp transition width of 0.2 K and a high critical current density of about 107 A cm−2 at 20 K and zero field, suggesting that this low-temperature process would be a promising technique for electronic devices operating at high temperatures above 20 K.

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