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Here we present a study of the pinning properties of high-quality single crystals of Ba(Fe1−xCox)2As2 (x = 0.07) by means of the quantitative magneto-optical imaging (MOI). This technique allows us to measure the magnetic field and supercurrent distribution as a function of the applied magnetic field and temperature, thus extracting the local parameters such as the critical current density, without any model assumption. Since values of the local supercurrent are obtained on the micron scale, we are able to observe evidence of anisotropic pinning both of intrinsic defects and extrinsic defects induced by high-energy heavy-ion irradiation. In fact, we find that these crystals naturally show anisotropic pinning due to intrinsic planar defects (whose presence is confirmed by the structural measurements through electron microscopy), and with quantitative MOI analysis we are able to analyze the effects of anisotropy coming from irradiation-induced defects. We quantitatively evaluated the dependence of the critical current density on the magnetic field direction with respect to the lattice principal axes. [ABSTRACT FROM AUTHOR]

In the context of superconducting electronics integrated with traditional silicon-based electronics we grew Si/YSZ/CeO2/YBa2Cu3O7-x architectures by means of the scalable magnetron sputtering growth technique. In this paper we report on structural, surface and electrical transport characterization of typical multilayers. We focus on the electrical transport characterization in the temperature range 18–30 K of c-axis YBa2Cu3O7-x films grown on top of several (001) oriented buffered substrates. The electric field vs. current density (E-J) curves exhibit step-like behaviour in correspondence to the transition between the non-dissipative and the flux-flow regimes. This trend is accompanied by the signature of linearly correlated pinning. On the other hand, in the flux-flow regime clear signatures of weak-link behaviour and current percolation are exhibited. In this complex framework possible future applications are discussed. [ABSTRACT FROM AUTHOR]

By using ac susceptibility measurements at different frequencies and dc fields we investigated the creep properties of MgB[SUB2] bulk samples. Two independent analysis have been used in order to determine the behavior of the pinning energy in the whole investigated temperature and field ranges. The main result of the first analysis (χ"-peak analysis) is that the attempt frequency v[SUB0] in the Arrhenius formula is about 10[SUP4] Hz, a value significantly lower than that usually reported for HTS's. By means of the second analysis a field dependent maximum of the pinning energy as a function of temperature has been found. It turns out that the phase points corresponding to the peak of the pinning energy are coincident with the irreversibility line, as determined by magnetization cycles. The results coming from different and independent analysis lead to the determination of a vortex-phase diagram for bulk MgB[SUB2], which seems to be largely dominated by creep phenomena. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the calibration procedure to be performed in order to extract from magneto-optical images the local values of magnetic induction and electric current density on a plane over and inside the superconducting sample respectively. The interaction between the spontaneous magnetization of the indicator film and the full magnetic field distribution in the specimen region has been considered. In particular, the generally disregarded interaction of the indicator film with in-plane magnetic fields, that is with the component parallel to the indicator surface, is retained in the model. The current density distribution is obtained by the numerical inversion of the Biot-Savart law. In order to incorporate the in-plane field effect into the inversion scheme, we have constructed an iterative procedure which successfully takes into account the full magnetic induction field. A set of experimental data on a high-temperature superconducting YBa[sub 2]Cu[sub 3]O[sub 7-x] film is presented to show the actual impact of the new analysis method, for what concerns both the local values of the magnetic induction and the electrical current density evaluation. [ABSTRACT FROM AUTHOR]

We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis. A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration, at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a network of strongly coupled Josephson junctions. [ABSTRACT FROM AUTHOR]

We present measurements of the magnetic field dependent microwave dissipation in a heavy-ion irradiated thin YBa[sub 2]Cu[sub 3]O[sub 7-δ] film, in order to study the effects of columnar defects on the pinning of vortices. Columnar defects were produced at 45° with respect to the c axis. Measurements of the microwave dissipation at 48 GHz were taken as a function of the angle between the field and the c axis, in order to compare the response along and perpendicular to the columns. The field was in the 0.3 T range. Several temperatures near the liquid nitrogen temperature were investigated. We find a dip in the dissipation when the field is aligned to the tracks. The dip is absent when the field is aligned perpendicular to the tracks, and with the same angle with respect to the crystallographic directions. The dip is not very sharp, and shows up for angles as far as 30° from the track directions. From the measurements, we estimate the pinning frequency along the columns at 80 K to be ν[sub pc] ... 25 GHz. [ABSTRACT FROM AUTHOR]

Good-quality melt-textured YBa[sub 2]Cu[sub 3]O[sub 7-x] materials with Y[sub 2]BaCuO[sub 5] nonsuperconducting inclusions were irradiated with 2GeV gold ions in order to produce a surface layer with columnar defects. The final goal is to gain a basic understanding of the role of the surface columnar defects in determining those magnetic properties of the materials that are related to the vortex confinement. The particle energy and the sample thickness were chosen in such a way that the percentage of irradiated volume is about 10%. In the paper the intrinsic structure and the damage morphology were analysed by means of transmission electron microscopy studies in both cross-section and plan-view geometry. As a result, the columnar defect density, size and shape were obtained. The irradiation produces parallel heavily damaged tracks whose diameter is between 3 and 6 nm. The overlapping of some columnar defects was highlighted and had to be taken into account to understand the superconducting properties of irradiated samples. The defects affect an implanted layer of about 50mum. The measured thickness coincides, within the experimental errors, with the thickness calculated by means of the Monte Carlo TRIM simulations. [ABSTRACT FROM AUTHOR]

YBCO melt textured samples were studied after Au ion irradiation of two opposite surface layers of the samples and after proton irradiation. The scaling behavior of the pinning force was studied in order to get information about mechanisms responsible for pinning in the studied samples. Correlated disorder introduced by surface ion irradiation is effective at high reduced temperatures and leads to the occurrence of a kink in the irreversibility line and to the shift of this line toward higher fields and temperatures. Enhancement of critical current density, increasing with temperature and field, was observed. Random disorder due to proton irradiation does not change the irreversibility line and only provides critical current enhancement decreasing with temperature and field. [ABSTRACT FROM AUTHOR]

We compare temperature and magnetic field dependence of the critical current density of melt textured YBCO, irradiated with monoenergetic 3.5 and 6.5 MeV protons, and with 235 MeV Au ions, respectively. The Au irradiation affected only a surface layer on the top and on the bottom of our bulk samples, i.e. a volume fraction ranging, in different specimens, from 5% to 13% of the total volume. The point-like defects produced J enhancements decreasing with the temperature up to a ( B, T) point where a crossover to damage occurs. On the contrary, surface columnar defects allow to control the vortex dynamics in the full sample, so that the critical current density enhancement increases as the temperature and the magnetic-field increase. While the addition of point-like defects does not significantly modify the irreversibility line (IL), the ILs of the Au irradiated samples present a shift towards higher temperature as well as smooth matching effects near the dose equivalent field. Magnetic relaxation rates and J measurements give results in accordance with recent theoretical findings. [ABSTRACT FROM AUTHOR]

The effects of proton irradiation on Nb-based Josephson junctions have been investigated. The fabrication technology employed is essentially the same of Josephson digital circuit designs, the main difference being a much lower Josephson critical current density. We have analysed in detail the magnetic field dependence of the junction critical current, and the quasiparticle tunnelling current, in order to observe possible occurrence of permanent changes produced by the ionizing particles. No evidence of radiation induced damage on the properties of the junctions has been found. The profile of the energy lost by protons within the Nb-targets and the dose is calculated by means of Monte Carlo simulations. A schematic description of the vacuum scattering chamber used for proton irradiation is also reported. [ABSTRACT FROM AUTHOR]

We have studied the effects of 235 MeVAu ion implantation on critical current density, creep rate and irreversibility line of YBCO melt-textured bulk samples. The fluence was 1.25·10 ions/cm, corresponding to a dose equivalent field of 2.5 T. We created two surface layers with correlated defects on the opposite sides of the sample, in such a way that the irradiated part was about 13% of the total volume. Such a surface irradiation caused a quite large widening of the irreversibility region in the B-T phase diagram. Critical current enhancements -having different behaviours as a function of field in different temperature ranges and reaching more pronounced values at higher temperatures and fields-were found. [ABSTRACT FROM AUTHOR]

This paper deals with a comparison of chemical, physical and mechanical characterisation of YBCO samples obtained with Temporary-Liquid-Densification Melt Growth (TLDMG). BaYCuO+50% excess BaYCuO pellets were prepared from different Ba-Y-Cu-O system phases, suitable to produce during the heat treatment temporary liquids at temperatures lower than 1000°C. A mechanical characterisation was performed in zero-field-cooling and field-cooling condition, showing hysteretic behaviour and creep of the levitation force. Measurements of magnetic hysteresis cycles in low fields and a.c. susceptibility were also performed. Some mechanical applications (high-speed electric motor and flywheel energy accumulator) were built and tested. The work now proceeds on two new industrial applications of melt-processed HTSC materials. [ABSTRACT FROM AUTHOR]

Bulk slabs of sintered YBCO were irradiated with monoenergetic protons at different energies (3.5 and 6.5 MeV) and different fluences, ranging from 1.8·10 to 8.6·10 p/cm. The effects on intergrain critical currents of protons crossing the sample and the effects of protons implanting in the specimen, has been studied by means of a.c. susceptibility characterizations. D.c. hysteresis cycles were measured in low fields in order to investigate the modifications in the intergrain critical current density due to proton implantation. The main result is the evidence that the intergrain J response to the applied field can be modulated by means of the proton irradiation. Resistive measurements were also performed in order to investigate the complex transport phenomena in polycrystalline materials. Irradiation-induced effects on both superconducting- and normal-state resistivity are studied. The addition of extrinsic defects can lead to enhanced transport properties, emerging especially when a magnetic field is applied. [ABSTRACT FROM AUTHOR]

A full set of facilities for transport characterisation of HTS as well as a set of crucial measurements are presented which point out the possible sources of errors of the «home-made» apparatus. The main characteristics are the automatisation of the whole data acquisition, the appositely designed hardware and software with suitable error messages, the on-line statistical treatment of data, the possibility of on-line optimisation of the current pulses and finally the availability of quasi-static temperature conditions in the R vs. T curves. The d.c. four-point method with bipolar d.c. pulsed current is employed. The experimental techniques chosen to obtain specific metrological achievements are discussed. [ABSTRACT FROM AUTHOR]

We irradiated both side of bulk melt textured YBCO with 235 MeV Au ions. The thickness of the specimens is significantly larger than the penetration range of the ions so that two surface layers of columnar defects are created. Critical current density enhancements were obtained in temperature and field ranges that are useful for applications. The boundary between reversible and irreversible regime is shifted toward higher temperatures. At higher fields the increase of the relaxation rate with temperature is less steep after irradiation. The general trends are independent of the thickness of the samples, at least in the range from 5% to 13% of volume affected by irradiation. [ABSTRACT FROM PUBLISHER]

We have experimentally investigated the effects of intense proton beam irradiation (up to 10/sup 15/ p/cm/sup 2/) on Josephson junctions and junction arrays. The devices we have studied were realized using state of the art full-Nb technology, employing same materials and thicknesses of common Josephson digital circuit designs. We have analysed in detail the magnetic field dependence of the junction critical current, and the quasiparticle tunneling current, in order to observe possible occurrence of permanent changes produced by the ionizing particles. No evidence of radiation induced damage on the properties of the junctions has been found. [ABSTRACT FROM PUBLISHER]