Structural and transport properties of epitaxial Ba(Fe_1−xCo_x)₂As₂thin films on various substrates

Abstract

A comprehensive microstructural study was conducted on optimally-doped epitaxial Ba(Fe 1 −x Co x ) 2 As 2 thin films grown by pulsed laser deposition on various substrates of a wide range of lattice constants: SrTiO 3 , LaAlO 3 , (La,Sr)(Al,Ta)O 3 , MgO, CaF 2 , and BaF 2 . We found that epitaxial strain directly affects the superconductivity in the film, with the transition temperature decreasing linearly with increasing in-plane lattice constant of the film. However, the strain is not determined by the lattice mismatch between the film and substrate. Instead, the mosaic spread of the grain orientation in the film and the thermal expansion coefficient of the substrate were found to correlate well with the in-plane lattice constant of the film. The result confirms the importance of structural distortions to the superconductivity in the Ba(Fe 1−x Co x ) 2 As 2 films.

Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

“…The main properties of the samples are summarized in Table I. All samples have good and comparable crystalline structure as determined by x-ray diffraction with small out-of-plane and in-plane full width at half maximum (FWHM): we determined Δω < 0.5° and Δϕ ~ 0.6° for the samples on CaF 2 and Δω < 0.4° and Δϕ ~ 0.7° for the samples on LSAT38.…”

“…of SrTiO 3 (named LSAT-S)182538 and one on (001)-oriented CaF 2 (named CaF-S). The multilayer film on STO-templated LSAT consisted of by 24 Co-Ba122/un-Ba122 bilayers (thickness ratio t Co-Ba122 :t un-Ba122 = 4:1) reaching a total thickness of ~400 nm (film named LSAT-M)2538. The multilayer film on CaF 2 was deposited with 24 bilayers of Co-Ba122/BaO-doped Co-Ba122 (thickness ratio t Co-Ba122 :t BaO-doped Co-Ba122 = 4:1) reaching a total thickness of ~350 nm.…”

“…37 the strain was correlated to a substrate/film lattice mismatch that, in the case of Co- Ba122, reaches 2.7%: in this work T c,0 ( T c at zero-resistance) was enhanced to more than 24 K and the self-field J c to ~1 MA/cm 2 at 10 K. Differently in ref. 38 the origin of the film strain was recently ascribed not to the direct lattice mismatch but to a more indirect thermal expansion mismatch due the larger thermal expansion coefficient of CaF 2 with respect to Co-Ba122 and other substrates. In order to study the effect of CaF 2 substrate on samples with modified pinning properties, we investigated single- and multi-layered Co-Ba122 thin films grown on CaF 2 and on SrTiO 3 -templated (La,Sr)(Al,Ta)O 3 (LSAT/STO)39.…”

Transport properties of ultrathin BaFe1.84Co0.16As2superconducting nanowires

“…As shown in Figure 4 [34].Therefore, the 10 nm thick Ba122:Co thin film grown on CaF2 substrate is suitable for exploring its application in the SNSPDs field in terms of film thickness and superconducting transition temperature required by SNSPDs.…”

Universal scaling behavior of the upper critical field in strained FeSe0.7Te0.3 thin films

“…T c as a function of the a-axis is shown in figure 2 for a number of FeSe 0.7 Te 0.3 films grown on the mentioned substrates. For comparison, values of optimally doped Ba(Fe 0.92 Co 0.08 ) 2 As 2 thin films on different substrates are also plotted [28]. The films have different a-axis lengths due to different in-plane compressive strain resulting mainly from the large thermal misfit between the substrates and the FeSe 1−x Te x layer [21,22,[28][29][30][31][32].…”