Structures in superconducting YBa2Cu3O7?? thin films investigated by magneto-optic technique (original) (raw)
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Nanosecond magneto-optic study of a new instability in thin YBa2Cu3O7−x films
Applied Physics Letters, 1993
We have investigated the dynamics of flux penetration into thin superconducting YBa2Cu307--x films using a magneto-optic technique with nanosecond time resolution. For films carrying large shielding currents an instability in the magnetic Aux distribution is discovered, which can be triggered by a local'perturbation, e.g., by a focused laser pulse. The instability develops in the form of fine ramified flux structures, with a propagation speed of the flux front on the order of 5 X IO4 m/s. Magnetic flux penetration into a superconductor has many practical implications, e.g., for the performance of superconducting coils or the shielding of magnetic fields. Related is the fact that a superconducting sample carrying the critical current density j, is in a state close to being unstable: Even a small local perturbation may hence rapidly quench the superconducting state over a major portion of the sample and can in this way give rise to an "explosive" penetration of flux into formerly well-shielded regions. We report here the first observations of the development of such an instability in thin HTSC films exposed to an external magnetic field in the 0.1 T range. It is found that under certain circumstances the flux distribution in the sample evolves into delicate ramified structures. The magnetic instability can occur as a spontaneous event, but can also be nucleated by heating the sample locally. Owing to the pronounced structure in the magnetic flux distribution, this phenomenon is not only relevant for the magnetic behavior of superconductors, but is of interest also from the general point of view of pattern formation in unstable systems.
Large area magneto-optical investigations of YBCO thin films
Review of Scientific Instruments, 1999
A new apparatus for magneto-optical investigations of high temperature superconducting ͑HTS͒ films as large as 20ϫ20 cm 2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field ͑magneto-optical scanning technique, MOST͒. The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1ϫ1 cm 2 is presented for the first time. The results are compared to inductive j c measurements as well as to micrographs ͓optical microscope ͑OM͒, scanning electron microscopy ͑SEM͔͒ and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical current density, which is the relevant parameter for an application of the superconducting thin films. Moreover, it could be shown that MOST has appreciable advantages compared to inductive j c scans and microscopy ͑OM, SEM͒. In particular it is possible to observe defects, which are below the optical resolution of the MOST setup.
Defects in YBa2Cu3O7−δ thin films studied by magneto-optics
Physica C-superconductivity and Its Applications, 1996
By means of the magneto-optical Faraday effect, flux-density distributions are observed in laser-ablated YBa2Cu30 7_ 8 thin films. The samples investigated are found to contain numerous defects of two different classes; (1) extended linear defects of weakly superconducting material and (2) small non-superconducting particles. The influence of these defects on the flux distributions is analyzed in detail using the concept of discontinuity lines of the currents [Th. Schuster et al. Phys. Rev. B 49 (1994) 3443]. The magneto-optical flux patterns clearly reveal that an application of a critical-state model to calculate the critical current density from magnetization data is impossible when a sample contains such defects. It is shown that even in the best samples the flux fronts are not homogeneous but consist of a large number of defect-induced parabolic flux plumes.
Magneto-Optical Studies of Ybco Thick Films in the Critical State
Magneto-Optical Imaging, 2004
We present magneto optical studies of the critical state in YBa 2 Cu 3 O 7-δ (YBCO) thick films prepared using BaF 2 ex-situ post reaction process. A fractal-like propagation was observed as the magnetic flux entering the superconducting films, in striking contrast to the behavior expected of a uniform type II superconducting film in the critical state. However, by averaging the flux density over a certain length scale, we found that flux penetration can be described with the standard Bean critical state model. The temperature dependence of critical current density J c was obtained by applying the Bean model to the averaged flux profiles, and found in good agreement with those obtained by direct transport measurements.
Growth and magnetic characterization of YBCO films
Il Nuovo Cimento D, 1994
Epitaxial films of YBa2 Cu3 07 -~ were deposited in situ on LaAI03 substrates using single-target 90 ~ off-axis sputtering. The films were characterized by magnetization measurements (M vs. T, H), applying the field parallel to c-axis. The observed differences in the T c and J~ values are attributed to the different oxygen content in the superconducting films.
Structural inhomogeneities in thin single-crystal films of YBa 2 Cu 3 O 7 − d are characterized using high resolution X-ray diffraction. Results of these measurements show a distribution in the c-axis lattice parameter and variations in the integrated intensities of (00ᐉ) diffraction peaks. Both effects can be interpreted as due to a variance in the oxygen content. Films prepared under identical growth conditions, when subjected to different post-annealing treatments showed varying structural and superconducting properties. A film with 7 − d close to 7.0 had a transition temperature (T c ) of 91 K, a width (DT c ) of 0.6 K, and a critical current density (J c ) of 6.5 × 10 6 A/cm 2 , whereas a film in which the oxygen content varied between 6.86 and 6.96 had a T c of 87 K, a DT c of 0.5 K, and a J c of 8.17 × 10 6 A/cm 2 . For each of the samples measured, the full width at half maximum (FWHM) of the (006) diffraction peak ranged between 340 and 2100 arc-seconds and was dependent on the method of preparation and the substrate. The J c s of these films were not sensitive to the quality of the film, as determined from the FWHM of the (006) peak, and the oxygen content, as determined from the (005) to (006) integrated intensity ratio. High resolution X-ray topographs showed uniform microstructure of the films, indicating that oxygen distribution is finely dispersed in the film. © 1997 Elsevier Science S.A.
IEEE Transactions on Applied Superconductivity, 2018
This study investigates chemically decorated surfaces as tools for the improvement of transport properties in superconducting YBa 2 Cu 3 O 7-x films. This approach, still to be thoroughly investigated, makes use of low-cost, easily-tunable chemical methods to obtain self-assembled oxide nanostructures on a substrate that will serve, in a second step, for the deposition of the superconducting film itself. The structures are supposed to produce in the superconducting matrix a specific amount of strain which is generally held responsible for the increased transport capacity of variously doped samples. For the growth of the nanostructures two different methods have been employed: Polymer Assisted Deposition (PAD) and Metal Organic Decomposition (MOD). The main advantages and disadvantages of these two routes are discussed. The oxide chosen for the deposition is one commonly used for artificial pinning in YBa 2 Cu 3 O 7-x , namely, Ba 2 YNbO 6 , together with the less common but highly interesting ferromagnetic compound La 0,77 Sr 0,33 MnO 3. We also show how the density of these nanostructures can be easily controlled and the necessary requirements for the growth of nanostructures are determined. A variety of crystalline substrates were tested for the deposition of the nanoparticles, such as SrTiO 3 , YSZ, MgO. YBa 2 Cu 3 O 7-x films have been deposited on selected samples via standard low-fluorine Metal Organic Decomposition and characterized SEM, XRD, VSM, DC resistivity and critical current measurements. The presence of the nanostructures results, in this case, in a slight increased value of J c which can be ascribed to the relatively low density of nanoparticles.
Physica C: Superconductivity, 1995
Epitaxial a-axis oriented YBazCu30 7_ ~ (YBCO) superconducting thin films have been grown by off-axis magnetron sputtering on Y203/YSZ/Si substrates with PrBa2Cu307_ ~ (PBCO) seed layer. The YBCO thin films were deposited immediately after the on-axis magnetron sputtering of PBCO. XRD analyses show that the a-axis volume fraction for 120 nm thick YBCO films varies with substrate temperature during PBCO deposition and its maximum value is higher than 98%. The TEM study shows the clear dependence between the character of the R-T dependence and the microstructure of our YBCO thin films, which varies with the change of the volume ratio of a-axis to c-axis oriented YBCO. 0921-4534/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4534(95)00514-5
Texture and magnetic anisotropy of YBa2Cu3O7-x film on MgO substrate
Journal of Materials Science: Materials in Electronics, 2020
The texture and magnetic anisotropy of a YBa2Cu3O7-x (YBCO) film growth onto a MgO substrate are analyzed in order to understand the relation between them. X-ray diffraction shows the presence of the (00l) reflections from the YBCO layer with a grain’s fraction value 98%. Rocking Curves (RC) measurements reveal an out-of-plane texture with a full width at the half maximum of 0.81°, revealing a high uniaxial texture in the YBCO film. The temperature dependence of the susceptibility measurements obtained under many applied fields along Hext ||c-axis and Hext||ab-plane reveals strong relationship between the uniaxial texture and the magnetic anisotropy, confirming the high ordering of the CuO2 superconducting planes. In addition, the critical current density values are obtained from the hysteresis loops and compared to similar YBCO films with uniaxial and biaxial texture reported elsewhere.
Journal of Crystal Growth, 1996
The surface morphology and the interface structure of superconducting YBaCuO thin films grown on SrTiO3 substrates by pulsed electron beam evaporation have been studied using scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The crystal structure and epitaxial orientation of the films have been analysed using X-ray diffraction. Parametric studies of the effect on the structural development of