Alternating current losses in biaxially textured YBa₂Cu₃O_7-δ films deposited on Ni tapes

YBa₂Cu₃O_7-δ films grown on rolling-assisted biaxially textured substrates carry critical current densities 10⁵-10⁶ A/cm² at 77 K and low applied magnetic fields. In the low-field and low-current regime, ac transport current studies show hysteresis energy loss (per cycle and per unit length) roughly the value expected for a superconductor of elliptic cross section. The critical current I_c was deduced from observed dc and dynamic current-voltage relations. The power loss rises sharply as I₀ (the maximum current in each cycle) is raised above I_c. In the present configuration, ferromagnetic hysteresis of the Ni substrate contributes little or no loss.