Thermally activated dissipation in Y₁Ba₂Cu₃O_7-x/Y₁Ba₂(Cu_1-xNi_x)₃O_7-x superconducting multilayer thin films

Heterostructures of Y₁Ba₂Cu₃O_7-x/Y₁Ba₂(Cu_1-xNi_x)₃O_7-x superconducting thin films have been grown on (100) yttriumstabilized ZrO₂ substrates using a pulsed laser deposition technique. The thickness of the Y₁Ba₂Cu₃O_7-x layer was changed from 120 Å to 420 Å, and the thickness of the Y₁Ba₂(Cu_1-xNi_x)₃O_7-x layer was varied from 85 Å to 480 Å, in order to investigate thermally activated dissipation behavior due to flux motion. The resistivity transitions of multilayers have been measured below T_c in magnetic fields up to 5 T. The electrical resistivity in magnetic field is thermally activated and shows a broad transition about 4 ∼ 5 K for magnetic field perpendicular to the c-axis and 8 ∼ 10 K for field parallel to the c-axis. The broadening of the resistive transition observed in multilayer thin films is shown to depend on both Y₁Ba₂Cu₃O_7-x and Y₁Ba₂(Cu_1-xNi_x)₃O_7-x layer thickness for both magnetic fields parallel and perpendicular to the c-axis. The activation energies derived from thermally activated flux flow are proportional to the Y₁Ba₂Cu₃O_7-x layer thickness up to 360 Å, but are inversely proportional to the increase of the Y₁Ba₂(Cu_1-xNi_x)₃O_7-x layer thickness when the other layers retain the same thickness.