Improvement of Flux Pinning Properties for Hafnium-Doped Gd123 Thin Films Fabricated by a Fluorine-Free MOD Method

In order to enhance the flux pinning force density F_p in magnetic fields for REBa₂ Cu₃ O_v (RE123)-coated conductors, Hf and Zr doping are the very valid way of introducing the perovskite nanostructure as artificial pinning centers (APCs) into the superconductors. However, the studies for Hf-doped RE123 thin films fabricated by the fluorine-free metal organic deposition (FF-MOD), which is the easiest production process, have not been done yet. In this study, we have successfully fabricated Hf-doped FF-MOD GdBa₂ Cu₃ O_v (Gd123) thin films on LaAlO3 substrates and investigated their flux pinning properties. Critical temperature for Gd123 thin films indicated around 92 K, and T_c varied little by Hf doping. Hf 10 mol% doped film achieved high critical current densities of 2.72 mA.cm^-2 at 77.3 K under 0 T, and 0.27 mA.cm^-2 at 77.3 K under 1 T. With increasing Hf-doping amount, F_p gradually increased, and the peak of Fp shifted to the high magnetic field side. The elementary pinning force and the effective pinning center density also increased. We believe that effective APCs, probably BaHfO₃ are introduced into FF-MOD Gd123 thin films by Hf doping.