Magnetization, Flux Creep and Transport in Tl-Ca-Ba-Cu-O Thin Films.

摘要

Static magnetization, flux creep, and electrical transport data are presented for thin films in the high-temperature superconducting Tl-Ca-Ba-Cu-O system. Unoriented polycrystalline 0.7 mu m-thick films of both Tl-2223 and Tl-2122 were prepared by sequential e-beam evaporation onto yttria-stabilized cubic zirconia and strontium titanate followed by careful post-deposition anneals. Low-field diamagnetic shielding shows very large demagnetization normal to the film, arising from current flow over macroscopic in-plane distances. Above 50 K there is negligible magnetization hysteresis consistent with easy flux motion. The magnetization exhibits a logarithmic time dependence due to activated flux creep with a small pinning energy of 0.083 eV. The transport properties are very different from those of polycrystalline YBa sub 2 Cu sub 3 O/sub 7-delta/ (Y-123) films. Tl-2223 films have shown critical current densities up to 240,000 A/cm sup 2 at 76 K (110,000 A/cm sup 2 for Tl-2122 films) with low sensitivity to in-plane magnetic fields and moderate sensitivity to perpendicular fields. This anisotropic behavior indicates that grain boundary Josephson junctions are not dominating the transport. The strong intergranular links and high critical current densities show the potential of these polycrystalline thin films for applications. 26 refs., 6 figs. (ERA citation 14:012370)