E. Reich

Ink-jet printing of YBa2Cu3O7 superconducting coatings and patterns from aqueous solutions

The objective of this paper is the development of ink-jet processing as a new technique for chemical solution deposition of YBCO coatings and patterns. Our research is mainly focused on the investigation and determination of the rheological parameters towards the printability of water-based inks in order to produce continuous YBCO coatings or multi-filamentary patterns on SrTiO3 substrates. A 0.185 mol L−1YBCO ink with a viscosity of 4.77 mPa s and a surface tension of 67.9 mN m−1, resulting in a ratio Re/We1/2 of 7.37, is developed. Its printing behaviour is further verified using a camera with strobed illumination to quantify the droplet velocity and volume. After optimization of the deposition parameters, a 350 nm thick YBCO coating showing preferential c-axis orientation could be grown on SrTiO3. This layer exhibits a critical current of 0.67 MA cm−2 at 77 K in self-field. Finally, the shape and dimensions of printed YBCO tracks were determined using optical microscopy and non-contact profilometry, showing 200 nm thick and 200 μm wide tracks.

Epitaxial LaFeAsO1−xFx thin films grown by pulsed laser deposition

Superconducting and epitaxially grown LaFeAsO1?xFx thin films were successfully prepared on (001)-oriented LaAlO3 substrates using pulsed laser deposition. The prepared thin films show exclusively a single in-plane orientation with the epitaxial relation and a full width at half-maximum value of 1?. Furthermore, resistive measurement of the superconducting transition temperature revealed a Tc,90% of 25?K with a high residual resistive ratio of 6.8. The preparation technique applied, standard thin film pulsed laser deposition at room temperature in combination with a subsequent post-annealing process, is suitable for fabrication of high quality LaFeAsO1?xFx thin films. A high upper critical field of 76.2?T was evaluated for magnetic fields applied perpendicular to the c-axis and the anisotropy was calculated to be 3.3 assuming single band superconductivity.

Versatile fluoride substrates for Fe-based superconducting thin films

We demonstrate the growth of Co-doped BaFe2As2 (Ba-122) thin films on CaF2 (001), SrF2 (001), and BaF2 (001) 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 for the films grown on CaF2 and BaF2 additionally by transmission electron microscopy. The superconducting transition temperature of the film on CaF2 is around 27 K, whereas the corresponding values of the films on SrF2 and BaF2 are around 22 K and 21 K, respectively. The Ba-122 on CaF2 shows almost identical crystalline quality and superconducting properties as films on Fe-buffered MgO.

Epitaxial LaFeAsOF thin films grown by pulsed laser deposition

Superconducting and epitaxially grown LaFeAsO1?xFx thin films were successfully prepared on (001)-oriented LaAlO3 substrates using pulsed laser deposition. The prepared thin films show exclusively a single in-plane orientation with the epitaxial relation and a full width at half-maximum value of 1?. Furthermore, resistive measurement of the superconducting transition temperature revealed a Tc,90% of 25?K with a high residual resistive ratio of 6.8. The preparation technique applied, standard thin film pulsed laser deposition at room temperature in combination with a subsequent post-annealing process, is suitable for fabrication of high quality LaFeAsO1?xFx thin films. A high upper critical field of 76.2?T was evaluated for magnetic fields applied perpendicular to the c-axis and the anisotropy was calculated to be 3.3 assuming single band superconductivity.

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high–field magnet applications

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 105 A/cm2 at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30–40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit.

Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2(001) substrate. High critical current density values – larger than 1 MA/cm2 in self field and liquid helium – are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through transmission electron microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what was observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction.

Nanocolumns in YBa2Cu3O7 − x/BaZrO3 quasi-multilayers: formation and influence on superconducting properties

The magnitude and anisotropy of the critical current density Jc as well as the irreversibility field Hirr of BaZrO3 (BZO)-doped YBa2Cu3O7 ? x?(YBCO) thin films are determined by both the amount of BZO and the deposition temperature. The influence of these two parameters was investigated on BZO/YBCO quasi-multilayers in two temperature series with different doping amounts (4 and 9?vol% BZO). The deposition temperature was varied between 790 and 850??C. The samples show an increase in Hirr, logarithmic peaks in Jc(B) and strong c-axis peaks in Jc(?). Nevertheless, the two series reveal opposite temperature trends for Jc: whereas Jc?increases with temperature for 4?vol% BZO, it decreases for 9?vol%. This is explained by a diffusion model for the formation and growth of BZO nanocolumns and an optimum balance between correlated and random pinning centres for high Jc. TEM images support this model.

Architecture, microstructure and Jc anisotropy of highly oriented biaxially textured Co-doped BaFe2As2 on Fe/IBAD-MgO-buffered metal tapes

Optimized, biaxially textured BaFe1.8Co0.2As2 thin films with an in-plane alignment of 1.7° have been realized on high-quality IBAD-textured MgO-coated technical substrates utilizing additional Fe buffer layers. High critical current densities (Jc) were achieved, comparable to films on single crystalline MgO (Jc ≥ 1 MA cm−2 at 4 K, self-field). Transmission electron microscopy investigations reveal a small number of c-axis correlated defects introduced by the MgO template. The effect of these defects on the Jc anisotropy was determined in angular-dependent electronic transport measurements.

Fabrication of superconducting oxypnictide thin films

Superconducting LaFeAsO1−xFx thin films were successfully deposited on (001)-oriented LaAlO3 substrates from stoichiometric polycrystalline LaFeAsO1−xFx targets with a fluorine concentration of up to x=0.25. For thin film fabrication we used pulsed laser deposition at room temperature in combination with a post annealing process. In this paper we present this technique in detail, which is successfully applied on thin film growth of the iron-based 1111LaFeAsO1−xFx compound. An extensive transmission electron microscopy analysis revealed further particulars about the formation and spacial distribution of the impurities. There are likewise promising results on growing superconducting GdFeAsO1−xFx thin films.

Unusually high critical current of clean P-doped BaFe2As2 single crystalline thin film

Microstructurally clean, isovalently P-doped BaFe2As2 (Ba-122) single crystalline thin films have been prepared on MgO (001) substrates by molecular beam epitaxy. These films show a superconducting transition temperature (Tc) of over 30 K although P content is around 0.22, which is lower than the optimal one for single crystals (i.e., 0.33). The enhanced Tc at this doping level is attributed to the in-plane tensile strain. The strained film shows high transport self-field critical current densities (Jc) of over 6 MA/cm2 at 4.2 K, which are among the highest for Fe based superconductors (FeSCs). In-field Jc exceeds 0.1 MA/cm2 at μ0H=35 T for H‖ab and μ0H=18 T for H‖c at 4.2 K, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar Tc. Structural investigations reveal no defects or misoriented grains pointing to strong pinning centers. We relate this unexpected high Jc to a strong enhancement of the vortex core energy at optimal Tc, driven by in-plane strain and doping...