High Critical Current Densities in MgB_2 Films Grown on Hastelloy Tape by Hybrid Physical-Chemical Vapor Deposition

摘要

We report on the high critical current densities in MgB_2 films directly grown on Hastelloy tapes without any buffer layer by using the hybrid physical-chemical vapor deposition method. MgB_2 films were formed by reaction of Mg metal vapor with the incoming B_2H_6 gas on the heated substrates. In MgB_2 films grown for 10 min at 500℃ in total working pressure 100 Torr with gas mixing ratio H_2:B_2H_6 = 70:30, we observed the transport critical current density (J_c) was approximately 10~6 A/cm~2 at 4 T and 20 K in magnetic fields applied parallel to the substrate plane. This value is higher than those observed in epitaxial MgB_2 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 MgB_2 films have a strong potential for high current applications.