# G. Ghigo's research while affiliated with INFN - Istituto Nazionale di Fisica Nucleare and other places

## Publications (205)

Article
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To reduce the use of carbon components sourced from fossil fuels, hemp fibers were pyrolyzed and utilized as filler to prepare EVA-based composites for automotive applications. The mechanical, tribological, electrical (DC and AC) and thermal properties of EVA/fiber biochar (HFB) composites containing different amounts of fibers (ranging from 5 to 4...
Article
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Short hemp fibers, an agricultural waste, were used for producing biochar by pyrolysis at 1000 °C. The so-obtained hemp-derived carbon fibers (HFB) were used as filler for improving the properties of an epoxy resin using a simple casting and curing process. The addition of HFB in the epoxy matrix increases the storage modulus while damping factor i...
Preprint
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Niobium is one of the most studied superconductors, both theoretically and experimentally. It is tremendously important for applications, and it has the highest superconducting transition temperature, $T_{c}=9.33$ K, of all pure metals. In addition to power applications in alloys, pure niobium is used for sensitive magneto-sensing, radio-frequency...
Article
EuFe2(As1−xPx)2 hosts complex dynamical processes resulting from the interplay of its two electronic ground states, i.e., ferromagnetism and superconductivity. A detailed understanding of the observed dynamics is, however, still missing. In this sense, frequency-resolved experimental techniques can be crucial to disentangle the magnetic and/or supe...
Article
The analysis of the radiation damage associated with energetic neutrons is a key factor for the application of glass-ceramics as joining materials in nuclear fusion plants. Triple ion beam irradiation is, currently, the only way to emulate the displacement damage and the effects of transmutation products induced by high energy neutrons at elevated...
Chapter
This chapter deals with the effects of disorder on the properties of IBS. Structural disorder enhances charge carriers scattering, affecting the material at the fundamental level, besides yielding to other application-relevant effects, such as vortex pinning. Ion irradiation is one of the most powerful tool to introduce disorder in a controlled way...
Chapter
This chapter deals with a combined experimental and theoretical analysis of the microwave-frequency electromagnetic response of different iron-based superconductor (IBS) families, namely BaFe2As2 with different substitutions (K in the Ba site, Co in the Fe site, and P in the As site) and stochiometric CaKFe4As4. Measurements, performed using a CPWR...
Chapter
In this chapter we report on the microwave analysis of the interplay between magnetism and superconductivity—one of the most intriguing topics in condensed matter physics—in single crystals of EuFe2(As1-xPx)2. This material, in a narrow range of composition shows coexisting ferromagnetism and superconductivity, with magnetic ordering at temperature...
Chapter
In this Chapter we show how we investigated the microwave properties of MgB2 and YBa2Cu3O7-x thin films by the analysis of CPWRs made from the films themselves. Concerning MgB2, the experimental results were interpreted within the framework of a two-band model in the presence of impurity scattering. We also showed that disorder, enhancing interband...
Article
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A microwave technique suitable for investigating the AC magnetic susceptibility of small samples in the GHz frequency range is presented. The method—which is based on the use of a coplanar waveguide resonator, within the resonator perturbation approach—allows one to obtain the absolute value of the complex susceptibility, from which the penetration...
Chapter
In this chapter we provide a brief overview of the main microwave techniques employed for the characterization of superconductors, with a focus on the use of resonant methods. Then, we report on the microwave methods we adopted to obtain the results discussed in the second part of the book, all based on the use of coplanar waveguide resonators (CPW...
Preprint
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We report on the investigation of the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ based on muon-spin spectroscopy and ac magnetic susceptibility ($\chi$) measurements. The dependence of the internal field at the muon site on temperature is indicative of a ferromagnetic ordering of Eu$^{2+}$ magnetic moments and only the convention...
Preprint
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The 12442 compounds are a recently discovered family of iron-based superconductors, that share several features with the cuprates due to their strongly anisotropic structure, but are so far poorly understood. Here, we report on the gap structure and anisotropy of RbCa2(Fe1-xNix)4As4F2 single crystals, investigated by a combination of directional po...
Article
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The 12442 compounds are a recently discovered family of iron-based superconductors, that share several features with the cuprates due to their strongly anisotropic structure, but are so far poorly understood. Here, we report on the gap structure and anisotropy of RbCa 2 (Fe 1− x Ni x ) 4 As 4 F 2 single crystals, investigated by a combination of di...
Article
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Superconductors are strategic materials for the fabrication of magnetic shields, and within this class, MgB2 has been proven to be a very promising option. However, a successful approach to produce devices with high shielding ability also requires the availability of suitable simulation tools guiding the optimization process. In this paper, we repo...
Article
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The development of responsive composite materials is among the most interesting challenges in contemporary material science and technology. Nevertheless, the use of highly expensive nanostructured fillers has slowed down the spread of these smart materials in several key productive sectors. Here, we propose a new piezoresistive PVA composite contai...
Article
The use of superconducting (SC) materials is crucial for shielding quasi-static magnetic fields. However, the frequent requisite of space-saving solutions with high shielding performance requires the development of a 3D modelling procedure capable of predicting the screening properties for different orientations of the applied field. In this paper,...
Article
Ion irradiation of superconductors allows both the establishment of their radiation hardness and the modification and optimization of their properties useful for applications. In this work, we investigate the effects of proton irradiation with different energies on Fe(Se,Te) thin films grown on CaF $_2$ and on buffered YSZ substrates. These system...
Article
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We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar—a cost effective and eco-friendly material—are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz-8 GHz. A proper permittivi...
Article
In this work, multi-functional coatings based on a UV-LED curable epoxy-acrylate resin and different loadings (namely, 1, 2.5, 5 and 10 wt.%) of carbonaceous structures having a peculiar porcupine (PuP)-like morphology were formulated and thoroughly characterized through thermal, dynamic-mechanical and electrical analyses. More specifically, biocha...
Article
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Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor, EuFe2(As1−xPx)2 (x = 0.23), were measured in pristine state and after different doses of 2.5 MeV electron or 3.5 MeV proton irradiation. The superconducting transition temperature, Tc(H), shows an extraordinarily large d...
Preprint
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Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor, $\textrm{EuFe}_{2}(\textrm{As}_{1-x}\textrm{P}_{x})_{2}$ (x = 0.23), were measured in pristine state and after different doses of 2.5 MeV electron or 3.5 MeV proton irradiation. The superconducting transition temperature...
Article
We report on the effects of thermal treatment of biochar embedded in epoxy-based composites on their microwave electrical properties, linking such properties to the material structure investigated by Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. Annealing temperatures in the range 900-1500°C and biochar concentrations in the epoxy...
Article
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We report on ion irradiation experiments performed on compounds belonging to the BaFe2As2 family, each one involving the partial substitution of an atom of the parent compound (K for Ba, Co for Fe, and P for As), with an optimal composition to maximize the superconducting critical temperature Tc. Employed ion beams were 3.5-MeV protons, 250-MeV Au...
Article
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Intermodulation distortion (IMD) of microwave signals incident upon a superconducting YBa2Cu3O7−x thin film sample on a LaAlO3 substrate is shown to relax as the sample magnetization also relaxes, revealing the signature of fluxon decay in the microwave distortion. The sample contained a microchannel of columnar defects that was introduced using he...
Article
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We report on the Eliashberg analysis of the electrodynamic response of Ba(Fe1−xRhx)2As2 single crystals across the disorder-induced s± to s++ transition. We previously experimentally identified the transition by its signature in the low temperature value of the penetration depth and observed a peculiar dependency of the critical temperature on diso...
Article
YBa 2 Cu 3 O 7 -based coated conductors (CCs) achieve the highest critical current densities ( J c ) of any known superconductor and are a key technology for applications such as rotatory machines, high-field magnets and power transmission. Incorporation of nano-sized non-superconducting second phases as additional vortex pinning centers has been c...
Article
We report on the anisotropy of the London penetration depth of CaKFe4As4, discussing how it relates to its electronic structure and how it modifies under introduction of disorder, both chemically induced (by Ni substitution) and irradiation induced (by 3.5-MeV protons). Indeed, CaKFe4As4 is particularly suitable for the study of fundamental superco...
Article
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We present the characterization and the numerical simulation of a high-temperature superconducting bolometer based on an YBa 2 Cu 3 O 7-x (YBCO) film, which is patterned in serpentine elements and selectively modified by means of micro-collimated high-energy heavy-ion irradiation. The local irradiation of YBCO yields to a controlled reduction of th...
Article
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Irradiation effects are often used to improve the effective pinning in superconductors, but sometimes they can reveal detrimental for superconducting properties. Fe(Se,Te) has been proven to be a very robust material against irradiation, in particular proton irradiation, thus configuring as an ideal material to work in harsh environments such as pa...
Article
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We report on the microwave analysis of the interplay between magnetism and superconductivity in single crystals of EuFe2(As1−xPx)2, accomplished by means of a coplanar waveguide resonator technique. The bulk complex magnetic susceptibility χm extracted through a cavity perturbation approach is demonstrated to be highly sensitive to the magnetic str...
Preprint
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We report combined experimental and theoretical analysis of superconductivity in CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ (CaK1144) for $x=$0, 0.017 and 0.034. To obtain the superfluid density, $\rho=\left(1+\Delta \lambda_L(T)/\lambda_L(0) \right)^{-2}$, the temperature dependence of the London penetration depth, $\Delta \lambda_L (T)$, was measured by usi...
Article
We report combined experimental and theoretical analysis of superconductivity in CaK(Fe1−xNix)4As4 (CaK1144) for x=0, 0.017, and 0.034. To obtain the superfluid density ρ=1+ΔλL(T)/λL(0)−2, the temperature dependence of the London penetration depth ΔλL(T) was measured by using a tunnel-diode resonator (TDR) and the results agreed with the microwave...
Article
Most iron-based superconductors are characterized by the s± symmetry of their order parameter, and are expected to go through a transition to the s++ state if enough disorder is introduced. We previously reported the observation of this transition in Ba(Fe1−xRhx)2As2 through a study of the disorder dependence of the critical temperature and low-tem...
Preprint
Most iron-based superconductors are characterized by the s+- symmetry of their order parameter, and are expected to go through a transition to the s++ state if enough disorder is introduced. We previously reported the observation of this transition in Ba(Fe1-xRhx)2As2 through a study of the disorder dependence of the critical temperature and low-te...
Article
Full-text available
We report on the combined experimental and theoretical analysis of the microwave-frequency electromagnetic response of BaFe2As2 single crystals with different substitutions: K in the Ba site (hole doping), Co in the Fe site (electron doping), and P in the As site (isovalent substitution). Measurements using a coplanar resonator technique lead to th...
Article
At the present day, iron-based superconductors (IBS) can be considered as competitors of cuprates for the fabrication of su-perconducting cables for high field application in the presence of particle irradiation. In particular, it has been demonstrated that 11 IBS are very robust against proton irradiation. In this work, we analyze the effect of th...
Article
We report on a combined experimental and modelling approach towards the design and fabrication of efficient bulk shields for low-frequency magnetic fields. To this aim, MgB 2 is a promising material when its growing technique allows the fabrication of suitably shaped products and a realistic numerical modelling can be exploited to guide the shield...
Article
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Microwave measurements of the London penetration depth and critical temperature Tc were used to show evidence of a disordered-driven transition from s± to s++ order parameter symmetry in optimally doped Ba(Fe1−xRhx)2As2 single crystals, where disorder was induced by means of 3.5 MeV proton irradiation. Signatures of such a transition, as theoretica...
Article
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We report on direct measurements of the energy gaps (carried out by means of point-contact Andreev reflection spectroscopy, PCARS) and of the critical temperature in thin, optimally doped, epitaxial films of BaFe2(As1-xPx)2 irradiated with 250 MeV Au ions. The low-temperature PCARS spectra (taken with the current flowing along the c axis) can be fi...
Article
The electrodynamic response of Ba1-xKxFe2As2 single crystals at the microwave frequencies has been investigated by means of a coplanar resonator technique, at different values of non-magnetic disorder introduced into the samples by heavy-ion irradiation. The surface impedance Z s = R s + iX s conforms to the classical skin effect above the critical...
Article
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In this paper we explore the effects of 3.5 MeV proton irradiation on Fe(Se,Te) thin films grown on CaF2. In particular, we carry out a systematic experimental investigation with different irradiation fluences up to 7.30x10^16 cm^-2 and different proton implantation depths, in order to clarify whether and to what extent the critical current is enha...
Article
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One of the open issues concerning iron-based superconductors is whether the s± wave model is able to account for the overall effects of impurity scattering, including the low rate of decrease of the critical temperature with the impurity concentration. Here we investigate Ba1−xKxFe2As2 crystals where disorder is introduced by Au-ion irradiation. Cr...
Article
We investigate the penetration depth of high-quality Ba1−xKxFe2As2 single crystals by a planar waveguide resonator technique, in a cavity perturbation approach. The experimental λL is compared to calculations based on the three-band Eliashberg equations within the s± wave model. To this end, the anisotropy of the penetration depth is taken into acc...
Article
We present a \asnmr Nuclear Magnetic Resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped ($x=$ 0.068) and overdoped ($x=$ 0.107) Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual r...
Article
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This paper compares the shielding properties of superconducting (SC) and superimposed superconducting/ferromagnetic (SC/FM) systems, consisting of cylindrical cups with an aspect ratio of height/radius close to unity. Both bilayer structures, with the SC cup placed inside the FM one, and multilayer structures, made up of two SC and two FM alternati...
Article
In this work, we present an approach towards achieving a detailed knowledge on the effects of irradiation in iron-based superconductors with high-energy heavy ions. Ba1−x K x Fe2As2 single crystals (x = 0.42) were irradiated with 250 MeV Au-ions. The crystals were shaped to be thin plates with thickness lower than the ion implantation depth and bas...
Article
In this work, an experimental approach toward reaching new insights into the mechanism of superconductivity in the iron-based compounds is presented. The temperature dependence of the penetration depth and of the microwave conductivity of high-quality Ba(Fe1-xCox)2As2 and (Ba1-xKx)Fe2As2 single crystals have been obtained by a 7.97-GHz superconduct...
Article
In this paper we investigate and compare the shielding properties of superconducting and hybrid superconducting/ferromagnetic systems, consisting of cylindrical cups with an aspect ratio of height/radius close to unity. First, we reproduced, by finite-element calculations, the induction magnetic field values measured along the symmetry axis in a su...
Article
CaO–Al2O3 (CA) and SiO2–Al2O3–Y2O3 (SAY) glass-ceramics are promising candidates for SiC/SiC indirect joints. In view of their use in locations where high radiation level is expected (i.e. fusion plants) it is important to investigate how radiation-induced damage can modify the material microstructure. To this aim, pellets of both types were irradi...
Article
We visualize, with a magneto optical imaging technique with indicator film, the local magnetic response of the compound La(Fe0.9Co0.015Si0.085)13 during its first order magneto structural transition. The technique allowed us by comparing the stray fields of the main magneto caloric phase and of secondary phases present in the sample to obtain the m...
Article
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Maximizing the sustainable supercurrent density, Jc, is crucial to high current applications of superconductivity and, to achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This...
Article
Magneto-optical imaging with an indicator film is used for investigating the magnetic pattern in ferromagnetic material specimens whose optical properties do not allow the direct visualization of their magnetic pattern. The magneto-optical indicator is a ferromagnetic film with low coercitivity that detects the magnetic field from a magnetic source...
Article
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Multiple versions can be downloaded from this site. The version available from www.hope.edu is the current version. Micro-channels of nanosized columnar tracks were planted by heavy-ion irradiation into superconducting microwave microstrip resonators that were patterned from YBa2Cu3O7-x thin films on LaAlO3 substrates. Three different ion fluences...
Article
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We investigate the temperature induced ferromagnetic to paramagnetic phase transition in Co substituted La(FexCoySi1−x−y)13 with x = 0.9 and low Co content of y = 0.015 (Tc≃200 K) by means of magneto-optical imaging with indicator film and by calorimetry at very low temperature rates. We were able to visualize the motion of the ferromagnetic (FM)/p...
Article
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 param...
Article
We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, $\lambda$, determine the solution. The calculated field reproduces qua...
Article
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 co...
Article
Microcollimated swift heavy-ion irradiation has been employed to carve channels with micron-sized width in YBa2Cu3O7-x(YBCO) superconducting coplanar microwave resonators. Comparative analysis of the first two resonant modes as a function of temperature, magnetic field, and input power was used to characterize the properties of the microchannels. A...