Francesco Laviano

CONTROL OF THE VORTEX MOVEMENT AND ARRANGEMENT BY OUT-OF-PLANE MAGNETIC STRUCTURES IN TWINNED YBa2Cu3O7−x/La0.67Sr0.33MnO3 BILAYER

In this article, we consider the magnetic interaction exerted on vortices in a thin YBa2Cu3O7−x film by a La0.67Sr0.33MnO3 layer. The magnetic coupling of the bilayer system was studied and locally imaged by means of magneto-optics. Twin boundaries in the LaAlO3 substrate cause a clear splitting of the manganite magnetic domains with well-defined in-plane magnetization separated by pinned out-of-plane magnetic structures. The vortices nucleated by the external magnetic field interact with the out-of-plane magnetic moments depending on their local structure and magnetic polarization. Different blocking mechanisms (sink or reservoir) are found for the vortex motion perpendicular to twin boundaries, whereas for vortices moving parallel to the out-of-plane magnetic structures either blocking or channelling effect is observed.

Nanostructuring superconductors by ion beams: A path towards materials engineering

The paper deals with nanostructuring of superconducting materials by means of swift heavy ion beams. The aim is to modify their structural, optical and electromagnetic properties in a controlled way, to provide possibility of making them functional for specific applications. Results are presented concerning flux pinning effects (implantation of columnar defects with nanosize cross section to enhance critical currents and irreversibility fields), confined flux-flow and vortex guidance, design of devices by locally tailoring the superconducting material properties, analysis of disorder-induced effects in multi-band superconductors. These studies were carried out on different kinds of superconducting samples, from single crystals to thin films, from superconducting oxides to magnesium diboride, to recently discovered iron-based superconductors.

Proton irradiation induced effects on YBCO films analysed by magneto-optics

In this paper we present a quantitative magneto-optical analysis on c-axis oriented YBCO thin films, as grown and irradiated with 3.5 MeV protons at three different fluences. Magneto-optical measurements were performed over the temperature range 5–70 K and at magnetic fields up to 150 mT. The local current density values were obtained from the field maps by means of the Biot-Savart law inversion. The critical current density (Jc) is locally defined as the current density where the maximum pinning efficiency is reached. This procedure allows obtaining Jc independently of dissipation threshold criteria or critical state model. A Jc enhancement emerges for irradiation at the lowest fluence ( Ф +2.5⋅1015 cm−2) in the whole investigate temperature range. On the contrary at increasing the irradiation dose a temperature-dependent crossover from an enhancement to a worsening of Jc is exhibited.

AN IRRADIATION FACILITY FOR IN-VACUUM HEAVY-ION IRRADIATION OF LARGE AREA SUPERCONDUCTORS

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 ...

Quantitative magneto-optical analysis of superconductors

A magneto-optical equipment has been set up and carefully calibrated. In this paper, we shortly review the main characteristic of this equipment, then we focus on the analysis to be performed in order to extract from magneto-optical images the local values of magnetic induction and electrical current density along the superconducting sample. This implies the numerical inversion of the Biot-Savart law. A detailed analysis modeling the interaction of the spontaneous magnetization across the indicator film with the magnetic fields in the specimen region has been performed. In particular, we take into account the generally disregarded interaction of the indicator film with in-plane magnetic fields, i.e. with the component parallel to the indicator surface. A set of experimental data on YBCO films is presents 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. A critical comparison of the new obta...