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Compared with mono-rare earth 123 films, ternary rare earth (Nd,Eu,Gd)Ba2Cu3O7−δ (NEG123) films show higher critical current density (Jc) and improved irreversibility field (Hirr), but no increase in the characteristic field corresponding to a crossover from a low-field plateau to a linear region in a log Jc–log H plot. At intermediate fields, Jc vs H scales as H(−0.5±0.05) for NEG123, in contrast to H(−0.73±0.05) for mono-rare earth samples such as Gd123. The slow power decay of Jc vs H together with the improved Jc and Hirr strongly implies that extra flux pinning centers exist in NEG123, which are thought to be noncorrelated stress fields induced by lattice mismatch.

We demonstrate the growth of Co-doped BaFe2As2 (Ba-122) thin films on AEF2 (001) (AE: Ca, Sr, Ba) single crystal substrates using pulsed laser deposition. All films are grown epitaxially despite of a large misfit of -10.6% for BaF2 substrate. For all films a reaction layer is formed at the interface confirmed by X-ray diffraction and by transmission electron microscopy. The superconducting transition temperature of the film on CaF2 is around 27 K, whereas the corresponding values of the other films are around 21 K. The Ba-122 on CaF2 shows identical crystalline quality and superconducting properties as films on Fe-buffered MgO., 5 pages, 6 figures, 2 tables

Ba(Fe1-xCox)2As2 superconducting thin films have been grown on SrTiO3, (La,Sr)(Al,Ta)O3, LaAlO3 and YAlO3 (YAO) single crystal substrates by pulsed laser deposition. All the films, except on YAO, have been grown epitaxially without buffer layers. The films deposited on YAO contained 45 degree in-plane rotated grains and showed a broad superconducting transition. The onset Tc of the films is observed to increase from 16.2 K to 24.5 K with increasing c/a, mainly due to a slight distortion of the AsFe4 tetrahedron. From this correlation, we expect that higher superconducting transition temperatures than 24.5 K in a strained epitaxial film may be possible., 4 figures, submitted to APL

A series of quasimultilayers of YBa2Cu3O7−δ(YBCO)∕Y2O3, namely, 70×[YBCO(m)∕Y2O3(n)] (m=40 pulse, and n=2, 5, 10, and 20 pulse) were prepared on single-crystal SrTiO3 using pulsed-laser deposition. X-ray diffraction measurements revealed that both in-plane and out-of-plane textures of YBCO in the present quasimultilayers are as good as in pure YBCO films. Nanoscale Y2O3 precipitates grow epitaxially inside YBCO. With increasing Y2O3 pulse number, Tc decreases slightly, while ΔTc remains less than 1.5K. As well, the YBCO lattice parameter c has an increasing trend with increasing n. This can be attributed to the effect of epitaxial strain induced by lattice mismatch. The flux pinning force density in films with lower Y2O3 content (such as n=2), is improved in large ranges of field and temperature. In contrast, films with high Y2O3 content show enhanced flux pinning only at low temperature, which is understandable from the temperature dependence of irreversibility fields.

Structural and transport measurements for quasimultilayers of Ir-doped YBa2Cu3O7−δ prepared by pulsed-laser deposition are presented. Due to metallic Ir doping, BaIrO3 particles form during film growth. These nanosized particles, having a perovskite structure, grow epitaxially in cube-on-cube relationship inside the film. A strong increase in pinning force density and, hence, Jc was found.