High critical current densities in MgB₂ films grown on hastelloy tape by hybrid physical-chemical vapor deposition

We report on the high critical current densities in MgB₂ films directly grown on Hastelloy tapes without any buffer layer by using the hybrid physical-chemical vapor deposition method. MgB₂ films were formed by reaction of Mg metal vapor with the incoming B₂H₆ gas on the heated substrates. In MgB₂ films grown for 10 min at 500 °C in total working pressure 100 Torr with gas mixing ratio H₂:B₂H₆ = 70:30, we observed the transport critical current density (J_c) was approximately 10⁶A/cm² at 4 T and 20 K in magnetic fields applied parallel to the substrate plane. This value is higher than those observed in epitaxial MgB2 films on sapphire substrates grown by using the same method. Magnetic field dependence of J_c of this sample was well explained by the grain-boundary pinning model. Our result opens up a possibility that the coated conductors made of MgB₂ films have a strong potential for high current applications.