Oxygen-annealing effects on superconducting properties of ErBa ₂Cu₃O_y, thin films fabricated by pulsed laser deposition method

We report crystallographic and electrical properties of ErBa ₂Cu₃O_y/SrTiO₃ (Er123/STO) films which were fabricated by the pulsed-laser-deposition (PLD) method in the temperature range of 720-780°C, and dramatic enhancement of critical current density (/c) by an oxygen post-annealing process. The PLD Er123/STO films were found to be crystallographically excellent in the deposition temperature region below 770°C from the intensity of diffraction peaks of 00l, the pole-figure of a reciprocal (102) plane and microstructures of the surface and the cross-section. Interestingly, in this temperature region, J_c values were clearly increased to the order of 10¹⁰ Am^-2 by oxygen post-annealing in comparison with those of the as-grown films (0.3∼0.6 × 10¹⁰ Am^-2). Enhancement of J_c was accomplished in a wide annealing temperature range of 350-500°C, which is corresponding with an annealing temperature range where the critical temperature shows over 90 K on a polycrystalline sample. On the other hand, Irreversibility fields were almost independent of the annealing temperature. These results indicated that insufficient carrier-doped region was partly existed even in a non-equilibrium process such as the PLD method. Therefore, homogenization of oxygen contents in a whole part of the Er123 film is crucially important for enhancement of critical current properties, which strongly suggests that the oxygen annealing is effective for improvement of functionality of devices in PLD-REBa₂Cu₃O, (RE: rare earth elements) thin films.