The Critical Current Density of ${rm GdBa}_{2}{rm Cu}_{3}{rm O}_{7-delta}$ Superconducting Films: Thickness, Temperature, and Field Dependences

摘要

The critical current density $(J_{c})$ of pulsed-laser-deposited ${rm GdBa}_{2}{rm Cu}_{3}{rm O}_{7-delta}$ (GdBCO) superconducting films with film thickness $(d)$ ranging from 0.2 to 1.5 $mu{rm m}$ was studied as functions of temperature $(T)$ and field $(H)$ . A thickness dependence of both the self-field and the in-field $J_{c}{rm s}$ at 77 K showed that the $J_{c}{rm s}$ were observed to decrease with increasing film thickness as an expression of $J_{c}sim d^{-1/2}$ , which was predicted by the collective pinning theory of uncorrelated defects. However, the in-field $J_{c}$ at $dsim 0.6~mu{rm m}$ was found to suddenly increase in the general trend of decreasing $J_{c}-d$ , which probably suggested a change in the pinning mechanism at that film thickness. The temperature dependence of the in-field $J_{c}$ in the GdBCO films was specifically studied at the low and the intermediate-field regions. A characteristic field H* separating the field-independent and the field-dependent $J_{c}$ regions was found to decrease with increasing both $T$ and $d$ . The value of $alpha$ of the $J_{c}sim H^{alpha}$ dependence in the intermediate-field region was estimated to be $alphasim 0.48$ –0.52 for both the thin- and the thick-film regions, which is similar to the theoretical value of $alpha=0.5$ for pinning by sparse point-like defects in ${rm REBa}_{2}{rm Cu}_{3}{rm O}_{7-delta}$ (RE: rare-earth elements) superconducting films. The value of $alphasim 0.35$ estimated for the 0.6 $mu{rm m}$ thick GdBCO film might suggest that effective pinning induced via nanosized dislocations formed on the surface of the GdBCO film. Based on the application of the theoretical models, it could be concluded that the dominant pinning mechanism in the GdBCO films is pinning by sparse uncorrelated defects.