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In this paper we investigate the behavior of the flux creep activation energy as a function of T, B and J in the temperature range from 4 K up to Tc. The experimental methodology is mainly based on ac susceptibility measurements at different frequencies and applied field, though some dc measurements are referred to along the discussion. A new analysis method is employed in the framework of the flux creep theory to explore the full range of temperature. It turns out that the key energy scale U0(T,B) at any external field exhibits a peak. The main outcome of the study is that the peak values are laying along the dc irreversibility line (IL) curve, while the points where U0=0 match the ac IL. Then these two curves divide the phase diagram in three reference regions to be investigated in details. [Copyright &y& Elsevier]

Studies the nanosize texture and transport properties in Y-Ba-Cu-O semiconductor thin films. Critical current density measurements; X-ray diffraction patterns of YBCO films; Pinning force as a function of the magnetic field at different temperatures.

Examines surface columnar defects on melt textured Y-Ba-Cu-O superconductors. Critical current density measurements; Time decay of magnetization; Field dependence of the critical current density.

This paper studies the striking correlation between nanosized structural patterns in YBCO films and macroscopic transport current. A nanosized network of parallel Josephson junctions laced by insulating dislocations is almost mimicking the grain boundary structural network. It contributes to the macroscopic properties and accounts for the strong intergranular pinning across the film in the intermediate temperature range. The correlation between the two networks enables to find out an outstanding scaling law in the (J[sub c], B) plane and to determine meaningful parameters concerning the matching between the vortex lattice and the intergranular defect lattice. Two asymptotic behaviors of the pinning force below the flux flow regime are checked: the corresponding vortex phases are clearly individuated. [ABSTRACT FROM AUTHOR]

An experimental set-up for magneto-optical analysis equipped with a new low- temperature controlling system is described. Magneto-optical investigations of the magnetic flux distribution are performed on as-grown as well as Au-on ion-irradiated Bi-2122 single crystals. The comparative analysis of as-grown and irradiated specimens shows that the magneto-optical technique provides information complementary to those provided by other techniques, such as, for example, susceptometric characterization. [ABSTRACT FROM AUTHOR]

Surface columnar defects, SCDs, are produced in high quality (Bi,Pb)[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub y]/Ag tapes by irradiating them with 0.25 GeV gold ions only on a top layer up to ≈15% of the full volume. The ion beam is orthogonal to the tape plane. In this paper we report experimental results of the surface implantation of columnar defects both in the high-current and in the lowcurrent regime with a particular emphasis on the influence of SCDs on the anisotropy dependent properties. Some characteristic labels of the SCD implantation are pointed out. A comparison between all the results in the two current regimes is made. A hint is given concerning analogous results obtained by means of transport electrical measurements. The experimental data can be interpreted by assuming that a new confined phase driven by SCDs sets up in both the current regimes. Acting on the dose, it is possible to obtain tunable control of the in-field performance in both regimes. [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]

The aim of this work is to investigate the mechanisms controlling the currentcarrying capability of YBa2Cu3O7[sub -delta] thin films. A comparison between the magnetic properties of as-grown films and films crossed by columnar defects, produced through 0.25 GeV gold-ion irradiation, is shown. The central issue concerns the investigation of the plateau-like features characterizing the log-log field dependence of the critical current density and the analysis of the irreversibility line. Data and models suggest that the inter grain pinning of the flux vortices channelling along a network of Josephson junctions dominates in the high-current low-temperature regime, while the intra grain pinning is effective near the irreversibility line. [ABSTRACT FROM AUTHOR]

The possibility to enhance in a predictable way the superconducting properties behavior of a bulk material by introducing linearly correlated defects within a surface layer has been demonstrated. Ag/BSCCO-2223 tapes were irradiated by means of 0.25 GeV Au ions at different fluences, with a dose equivalent field Bθ ranging from 1 T to 5 T. The implantation depth was about 15 µm corresponding to about 15% of the total sample thickness. Sample independent enhancements of different a.c and d.c properties show up, due to vortex confinement in the whole sample. The sample independence exhibited by all the experimental findings as well as, on the other side, the dose dependence of the enhancements, allow to design in advance the performances of a monofilamentary tape where defect trenches of nanometric size are scratched. [ABSTRACT FROM AUTHOR]

The critical current J[sub c] of superconducting films is about two order of magnitude larger than that of single crystals. The dependence of such J[sub c] on field depends on the presence and distribution of defects. We speculate that High Temperature Superconducting (HTS) films can be modeled as an agglomeration of islands coupled via Josephson contacts and then considered as a network of Long Josephson Junctions (LJJ) between superconducting islands. In order to check this hypothesis we further developed a model firstly introduced by Fehrenbacher based on the modulation of critical current densities in LJJ by means of suitable distribution of defects. The defects act by modulating the coupling energy of the junction. Critical current densities are calculated in the case of periodic and random defect distributions. [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]

Abstract: High-energy heavy-ion beams collimated by means of laser cut stainless-steel masks create microsize mesas surrounded by virgin regions into strip-shaped YBCO films. The ions induce columnar nanostructures whose density is tailored to generate locally weaker superconductivity. FESEM and AFM analyses show evidence of interface boundary regions with upward steps of about 20nm. The mesas exhibit magneto-resistive performances, functional to localize and confine external electromagnetic excitations. This leads to envisage a road map aimed at using just superconducting electrodynamics for electromagnetic detection. [Copyright &y& Elsevier]

Abstract: The electromagnetic coupling between the magnetic and the superconducting layers in perovskite-heterostructures was investigated by means of the magneto-optical technique. The quantitative imaging of the magnetic field distribution allows the high resolution reconstruction of local supercurrent density. Two phenomena arising from the coupling between the manganite layer and the YBCO superconducting film deposited on top were investigated, i.e., the local effects of the electronic coupling between the compounds and the interaction of manganite magnetic moments on vortices in the superconductor. The first issue can be quantified in terms of the local superfluid density depression/enhancement in correspondence of the underlying magnetic structure, both domains and domain-walls (in dependence on the orientation and sign of the local magnetization) and of the spontaneous, macroscopic screening current loops generated by the manganite domain-walls. The interaction between the local manganite magnetization and the superconducting vortices is also influenced by structural defects because they modulate the magnetic pattern of the manganite. Different channeling phenomena in correspondence of natural twin-boundaries of the substrate, but locally magnetized by pinned domain-walls of the manganite on their locations, were recognized. In particular, it turns out that the vortex density along magnetized twin-boundaries can be controlled by the underlying magnetic moment orientation. [Copyright &y& Elsevier]

In this work we show how strongly the interaction between pancakes in the ab-planes and Josephson vortices (JVs) across them is affected by columnar defect (CD) implantation, due to heavy-ion irradiation. By means of the irreversibility temperatures, obtained by the onset of the third harmonic of the a.c. susceptibility, the Bose-glass transition is put in evidence. This transition is limited in phase space size by the JV density, modulated by increasing the in-plane component of the applied field, in Ag/BSCCO-2223 tapes irradiated with 0.25 GeV Au-ions producing CDs reaching the 15% of the depth of the tape. [Copyright &y& Elsevier]