Synthesis, structure, and magnetic characterization of pulsed laser-ablated superconducting La2CuO4Fx thin films

High quality, c-axis oriented thin films of semiconducting La2CuO4 have been fabricated by pulsed laser-ablation deposition. Superconducting properties have been successfully induced in the films by a postdeposition, ex-situ static annealing process in a F2/N2 gas mixture. The influence of the fluorination temperature on the structural, magnetic, and electronic properties of the resulting thin films has been examined in detail. X-ray data reveal that facile fluorination of the films proceeds via a complex, multistage process, often yielding to distinct La2CuO4-type phases. This phase segregation suggests a disproportionation process following fluorine uptake. Such a disproportionation is subtly different from that found for oxygen excess La2CuO4 in that for La2CuO4+δ the parent O4 and an oxygen rich (O4+δ) phase are formed, but in the present system two fluorinated (i.e., oxidized) phases are formed. La2CuO4 thin films fluorinated at a temperature of 150 C possess the highest values for both Tc (onset) (ca. 38.5 K) and critical current density (>106 A cm-2 at 4.2 K in zero magnetic field). Magnetic susceptibility data demonstrate that this fluorination methodology is of sufficient sensitivity to allow the controlled hole-doping of semiconducting La2CuO4 thin films through to the high-temperature superconducting regime