Effect of Oxygen Depletion on the Pinning Properties of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{\rm x}$ Films With Nanoinclusions

Applications of YBa₂Cu₃O_x (YBCO) coated conductors require strong vortex pinning to ensure a non-dissipative state over a large range of temperatures and magnetic field values. Incorporations of nanoparticles and nanorods have generally resulted in a substantial increase of pinning, but the actual mechanism producing this increase is not fully understood. This report addresses the origin of the enhanced pinning through comparative resistive measurements in the mixed state of thin films of YBCO, YBCO doped with Y₂O₃ nanoparticles, and YBCO doped with BaSnO₃ nanorods. In order to study the effect of oxygen, all three kinds of samples have been annealed in air at 420°C. We have extracted and compared the resistive irreversibility lines before and after annealing. Our results indicate that while the nanoinclusions in the fully-oxygenated samples improve the pinning strength over that in the pure YBCO sample, the pinning enhancement essentially vanishes upon oxygen depletion. This is true for both pinning structures, nanorods and nanoparticles.