Enhanced flux pinning of air-processed Gd123 by doping ZrO 2 nanoparticles

Abstract

Nano-sized centers for magnetic flux pinning were successfully introduced into a bulk superconductor GdBa 2Cu 3O 7− δ (Gd123) by mixing ZrO 2 nanoparticles with precursor prior the melt growth in air. Superconducting properties and structure of doped Gd123 were studied by magnetization and transmission electron microscopy, respectively. The critical current density ( J c) and critical temperature indicate that the optimum addition amount is 0.2–0.8% ZrO 2 in molar ratio to Gd123 as composition. With 0.4 mol % ZrO 2 addition, J c was increased to 100,000 A/cm 2 at 77 K under self-field. The normalized pinning force deduced from the magnetization as a function of applied magnetic field shows single peak. Thus, the nano-sized ZrO 2 addition enhanced the normal core pinning under low magnetic field, B/ B irr < 0.2. Particles with <50 nm in diameter were observed and assigned as BaZrO 3 particles locating inside single domain Gd123. The present result may assess that BaZrO 3 nanoparticles or associated defects plays a role of pinning centers within a comparable range with the coherence length ξ.