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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 this paper we present a magneto-optical analysis of local current densities in YBCO films, before and after 3.5 MeV proton irradiation. The main issue consists into measuring and interpreting the temperature dependence of the critical current density (Jc) in samples with different, increasing defect density. Proton irradiation adds more point defects into the as-grown films. The new defect density as well as the related strain-induced modifications of the order parameter are pushed in our experiment up to temperature-modulated damage thresholds. First of all model-independent Jc data were analysed in the framework of different pinning models, all of them based on mechanisms related to the temperature induced change of the effective pinning centre distribution as well as to the shape of single pinning wells. It turns out that in such a framework the fit parameters are, generally speaking, not suitable to interpret the changes of the pinning landscape across the whole investigated temperature range. Then a model based on a vortex distribution across the whole sample, resulting in a current density that mirrors the current through a defect-modulated average short Josephson junction (JJ) row, is successfully tried. The Jc dependence in the whole temperature range and for all the considered defect densities is accounted for by means of a coherent set of fit parameters. It turns out that the chief quantity that allows applying the JJ formalism to a vortex distribution across the defected matrix is a suitably defined temperature-dependent magnetic thickness of the junctions, which substitutes the usual magnetic penetration in JJs. [ABSTRACT FROM AUTHOR]

In this paper we investigate the effects of ion irradiation on the superconducting properties of polycrystalline highdensity MgB[sub 2]. We show that the investigated samples are quite radiation hard, both for what concerns the main reference superconducting parameters and, more important, for what concerns the details of the basic vortex dynamics. This property makes magnesium diboride a good candidate for applications in outspace and in harsh environments. The focus of the analysis is on the flux creep phenomena, studied by ac susceptibility measurements at different frequencies and applied fields. The employed analysis method allows obtaining the activation energy as a function of temperature, field and current density, in their full ranges. As a result, vortex-phase diagrams for the unirradiated and the irradiated samples can be compared and discussed. [ABSTRACT FROM AUTHOR]

An irradiation facility to irradiate "long" stripe-shaped high-Tc superconductors by means of GeV heavy ions is described. This facility was designed and installed at INFN - Laboratori Nazionali del Sud (LNS), Catania, Italy. It consists into a moving apparatus automatically driven at a given velocity in order to obtain the in-vacuum exposure of contiguous zones of the moving target at a programmed ion fluence. The whole apparatus is automatically controlled by a home-made remote control program. The main parts of the apparatus are the mechanical set-up and the electronic circuit to create feedback signals to control both the beam current and the velocity of the sample holder, the high accuracy system for the measure of the integrated charge and the beam calibration set-up (beam shape and homogeneity). This apparatus is, at our best knowledge, the first one especially designed to create nanostructures across "large area" superconducting devices by means of the irradiation. Some significant results of 4.2 GeV Au-ion irradiation of a long high-Tc superconducting multifilamentary Ag/BSCCO-2223 tape are shown. [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]

Investigates the vortex confinement mechanisms in melt-textured YBa[sub 2]Cu[sub 3]O[sub 7-x] with ion induced surface nanostructuring. Analysis on the magnetic property of the material before and after irradiation; Relationship between surface columnar defects and intrinsic defects; Use of Dew-Hughes model.

Abstract: We report effects of particle energy on physical properties of Co-doped BaFe2As2 in the case of Xe and Au irradiations. The irradiation-induced suppression of T c is found to be related with several factors, such as defect structures and the thickness of the crystal. Heavy-ion irradiation induces enhancement of critical current density J c , and a weak dip in the hysteresis loop. The fish-tail effect is completely suppressed by a modest density of defects. The enhancement of J c is closely related to the defect structure. Namely, splayed structure in columnar defects, inevitably introduced at lower energies, results in a strong enhancement of J c by forced entanglement of vortices. [Copyright &y& Elsevier]

Abstract: The paper reports on a high precision equipment designed to modify over 3-dimensions (3D) by means of high-energy heavy ions the local properties of thin and thick films. A target-moving system aimed at creating patterns across the volume is driven by an x–y writing protocol that allows one to modify beam sensitive samples over micrometer-size regions of whatever shape. The moving system has a mechanical resolution of 15nm. The issue of the local fluence measurement has been particularly addressed. The setup has been checked by means of different geometries patterned on beam sensitive sheets as well as on superconducting materials. In the last case the 3D modification consists of amorphous nanostructures. The nanostructures create zones with different dissipative properties with respect to the virgin regions. The main analysis method consists of magneto-optical imaging that provides local information on the electrodynamics of the modified zones. Features typical of non-linear current flow hint at which pattern geometry is more functional to applications in the framework of confined nanostructuring of superconducting films. [Copyright &y& Elsevier]

This paper studies the effects of defects induced by 6 MeV protons on high-density pellets of MgB2. This methodology is useful to test the possibility to hinder the in-field decay of critical current density through extrinsic pinning centers as well as to check the radiation hardness of this material.Magnetic properties of two twin samples, the first one as-grown, the second one irradiated at a fluence of 0.8×1016 p/cm2 were measured and compared.The main outcome of the study is that this high-density material is quite hard with respect to irradiation with medium-energy proton beams. This makes MgB2 a good candidate for out-space applications.However some little modulation, either damage or enhancement, of the magnetic properties is observed. The impact of the effect is not sufficient to prevent the in-field decay of the magnetization, although it presents some interesting characteristics worth to be discussed in a framework of comparison with analogous results on HTSC. In particular, the results suggest some correlation between defects along the beam path. The main open issue concerns the existence of “hidden weak links”, hinted by the field dependence of the high-temperature persisting damage. [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]