AC inductance measurements of high-temperature superconductor thin films in DC magnetic fields

Abstract An AC inductance technique combined with a variable DC magnetic field has been used to measure at 77 K the flux exclusion properties of thin films of the high-temperature superconductors YBa 2 Cu 3 O 7− x and Tl 2 Ba 2 CaCu 2 O 8 , prepared by coevaporation, in situ off-axis sputtering, or laser ablation. These results are compared to those for single crystal YBa 2 CaCu 3 O 7− x . A decrease in flux exclusion with applied DC field is seen for all samples, most strongly for Tl 2 Ba 2 CaCu 2 O 8 films. The change in flux exclusion with magnetic field varies widely for YBa 2 Cu 3 O 7− x samples, with some laser-ablated films showing less change in flux exclusion with magnetic field than single crystal YBa 2 Cu 3 O 7− x . These results are interpreted in terms of magnetic field penetration through crystalline structures and grain boundaries in these materials.