Synthesis, Structure, and Magnetic Characterization of Pulsed Laser-Ablated Superconducting La2CuO4Fx Thin Films

Abstract

High quality, c-axis oriented thin films of semiconducting La{sub 2}CuO{sub 4} 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 F{sub 2}/N{sub 2} 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 La{sub 2}CuO{sub 4}-type phases. This phase segregation suggests a disproportionation process following fluorine uptake. Such a disproportionation is subtly different from that found for oxygen excess La{sub 2}CuO{sub 4} in that for La{sub 2}CuO{sub 4+{delta}} the parent O{sub 4} and an oxygen rich (O{sub 4+{delta}}) phase are formed, but in the present system two fluorinated (i.e., oxidized) phases are formed. La{sub 2}CuO{sub 4} thin films fluorinated at a temperature of 150 C possess the highest values for both T{sub c} (onset) (ca. 38.5 K) and critical current density (>10{sup 6} A cm{sup {minus}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-dopingmore » of semiconducting La{sub 2}CuO{sub 4} thin films through to the high-temperature superconducting regime.« less