Roberto Gerbaldo

The DC magnetic shielding properties of a commercial Pb-doped Bi 2 Sr 2 Ca 2 Cu 3 O 10 + x (Bi-2223) cup were investigated under axial, transverse, and crossed magnetic field configurations. Particular attention was devoted to the role of the magnetization history, which was shown to significantly influence the ability to shield a magnetic field applied orthogonal to the direction of the first magnetization process. A progressive reduction of the shielding capability was observed with increasing field applied in the pre-magnetization process, revealing distinct regimes associated with the evolution of the internal current distribution. The superimposition of a ferromagnetic (FM) cup was found not only to strongly increase the maximum shielded field—from 8.2 to 144 mT in the transverse orientation and from 11.5 to 68 mT in the axial orientation—but also to markedly reduce these history dependent effects, leading to a more stable shielding performance over a wide range of pre-magnetization field values. To understand these results, a three-dimensional numerical approach based on the vector potential ( A ) formulation was developed and validated by comparing the computational output with the experimental data. The simulations provide insight into the underlying mechanisms, highlighting the competition between magnetization-induced and shielding currents and their impact on the final current density distribution. These findings clarify the role of magnetization history in Bi-2223 magnetic shielding and demonstrate the effectiveness of hybrid superconducting/FM configurations for improving performance under realistic operating conditions.

The ability of MgB₂ polycrystalline samples to carry strong current densities even across high-angle grain boundaries has boosted the fabrication of large bulk superconductors. However, the occurrence of thermomagnetic instabilities, such as flux jumps, compromises the use of this compound at low working temperatures. Investigating and mitigating these phenomena are then crucial for future applications, as for instance permanent bulk magnets. In this paper, starting from the experimental evidence of flux-jump occurrence in a MgB₂ disc-shaped magnet prototype, we numerically investigated this phenomenon coupling the electromagnetic equations (formulated using the magnetic vector potential) to the heat diffusion equation. This numerical approach – validated via the comparison between computed and experimental results – provided us with the evolution of the local magnetic field and temperature in correspondence to a flux-jump. Based on this information, we finally investigated possible solutions to prevent flux-jump occurrence through the improvement of the thermal exchange between the sample and the cooling stage.

The combination of conductive carbon together with magnetic particles is a consolidated strategy to produce cutting-edge fillers for the production of polymer composites able to shield against microwave radiation. In this work, we developed and characterized an iron-tailored biochar obtained from the pyrolysis of olive pruning which was added as filler for the preparation of epoxy composites. The biochar-based composites were obtained by keeping the filler concentration at 10 and 40 wt.%. An extensive characterization was carried out in order to assess the electrical and magnetic properties of the composites containing biochar and iron-tailored biochar. The highest DC electrical conductivity of 59 mS/m was observed in the 40 wt.% iron-tailored biochar-loaded composite, while the reduction of the filler loading led to a drastic reduction in conductivity: 60 μS/m in the 10 wt.%-loaded composite. Ferromagnetic behavior of composites containing iron-tailored biochar is visible in the emerging hysteretic behavior, with a magnetic signal increasing with the filler concentration. Finally, both the complex permittivity (ε’) and the AC conductivity (σ) are enhanced by increasing the BC filler amount in the matrix, regardless of the presence of iron.

Aim: The design of new hybrid nanoplatforms (HNPs) through the innovative and eco-friendly use of tannic acid (TA) for the synthesis and stabilization of the nanoplatforms. Materials & methods: The... Plain language summary The aim of this research was to prepare new nanoparticles (called nanoplatforms) made from two parts: a magnetic core and the addition of gold particles. These particles can ...

Waste stream valorization is a difficult task where the economic and environmental issues must be balanced. The use of complex metal-rich waste such as red mud is challenging due to the wide variety of metal oxides present such as iron, aluminum, and titanium. The simple separation of each metal is not economically feasible, so alternative routes must be implemented. In this study, we investigated the use of red mud mixed with hemp waste to produce biochar with high conductivity and good magnetic properties induced by the reduction of the metal oxides present in the red mud through carbothermal processes occurring during the co-pyrolysis. The resulting biochar enriched with thermally-reduced red mud is used for the preparation of epoxy-based composites that are tested for electric and magnetic properties. The electric properties are investigated under DC (direct current) regime with or without pressure applied and under AC (alternating current) in a frequency range from 0.5 up to 16 GHz. The magnetic measurements show the effective tailoring of hemp-derived biochar with magnetic structures during the co-pyrolytic process.

The use of superconducting (SC) materials is crucial for shielding quasi-static magnetic fields. However, the need for space-saving solutions with high shielding performance requires the development of a three-dimensional (3D) modelling procedure capable of predicting the screening properties for different orientations of the applied field. In this paper, we use a 3D numerical model based on a vector potential formulation to investigate the shielding ability of SC screens with cylindrical symmetry and a height/diameter aspect ratio close to unity, without and with the superimposition of a ferromagnetic (FM) circular shell. The chosen materials were MgB₂ and soft iron. First, the outcomes of the calculations were compared with the experimental data obtained with different shielding arrangements, achieving a notable agreement in both axial field (AF) and transverse field (TF) orientations. Then, we used this validated modelling approach to investigate how the magnetic mitigation properties of a cup-shaped SC bulk can be improved by the superimposition of a coaxial FM cup. Calculations highlighted that the FM addition is very efficient in enhancing the shielding factors (SFs) in the TF orientation. Assuming a working temperature of 30 K and using a layout with the FM cup protruding over the SC one, SFs up to eight times greater than those with a single SC cup were attained at applied field up to 0.15 T, reaching values equal to or higher than 10² in the inner half of the shield. In the AF orientation, the addition of the same FM cup incurs a modest worsening at low fields, but at the same time it widens the applied field range where SF ⩾ 10⁴ occurs near the close extremity of the shield to over 1 T.

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 depth and the superfluid density can be determined. We report on the characterization of several iron-based superconducting systems, belonging to the 11, 122, 1144, and 12442 families. In particular, we show the effect of different kinds of doping for the 122 family, and the effect of proton irradiation in a 122 compound. Finally, the paradigmatic case of the magnetic superconductor EuP-122 is discussed, since it shows the emergence of both superconducting and ferromagnetic transitions, marked by clear features in both the real and imaginary parts of the AC susceptibility.