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Synthesis, Design, Characterization of Unconventional Superconducting Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Simulation and Design".

Deadline for manuscript submissions: closed (10 February 2022) | Viewed by 12551

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Prof. Dr. Gianluca Ghigo

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Guest Editor

Politecnico di Torino, Department of Applied Science and Technology, Torino 10129, Italy
Interests: experimental superconductivity; microwave characterization techniques; materials engineering by ion irradiation; use of ion-beams-induced disorder to study the properties of unconventional superconductors

Dr. Daniele Torsello

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Guest Editor

1. Politecnico di Torino, Department of Applied Science and Technology, 10129 Torino, Italy
2. Italy Istituto Nazionale di Fisica Nucleare, Sezione di Torino, 10125 Torino, Italy
Interests: superconducting materials; nuclear fusion technology; radiation damage; microwave superconductivity
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Dear Colleagues,

Superconductors have fascinated researchers all over the world for the last century, leading to the quest for new material classes with increasingly interesting and peculiar physical properties, and with improved potential for applications. In recent years, extensive research efforts have been devoted to the so-called unconventional superconductors, materials characterized by at least one feature among multiband superconductivity, triplet spin state, non-phononic coupling, and coexistence of superconductivity and magnetism.

Together with the great number of studied compounds, new computational and experimental techniques have been developed and improved to allow the successful design and synthesis of materials with enhanced performances. The progress necessarily also involved characterization techniques, which became more precise and reliable to probe a wider spectrum of physical properties. Finally, simulations and theoretical modelling gave the needed framework to interpret experimental data and to predict further progress.

To resume the achievements of recent years in this field, the current Special Issue proposes to cover all aspects connected with the synthesis, design, and characterization of unconventional superconductors.

It is our pleasure to invite you to submit a manuscript for this Special Issue, welcoming full original research papers, communications, and review articles, to be submitted before 31 July 2021.

Prof. Dr. Gianluca Ghigo
Dr. Daniele Torsello
Guest Editors

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Keywords

unconventional superconductivity
synthesis of superconductors
experimental superconductivity
applied superconductivity
techniques for the characterization of superconductors

Published Papers (6 papers)

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Research

13 pages, 1813 KiB

Open AccessArticle

Ferromagnetism and Superconductivity in CaRuO₃/YBa₂Cu₃O_7-δ Heterostructures

by Alina Marinela Ionescu, Ion Ivan, Claudiu Locovei, Melania Onea, Adrian Crisan, Soltan Soltan, Gisela Schütz and Joachim Albrecht

Materials 2022, 15(7), 2345; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15072345 - 22 Mar 2022

Viewed by 2271

Abstract

The deposition of a ferromagnetic layer can affect the properties of high-temperature superconductors underneath. We investigated the influence of ferromagnetic CaRuO₃ on the properties of YBa₂Cu₃O_7-x (YBCO) superconducting thin films when the layers are either in direct contact or separated by a barrier layer of 5 nm SrTiO₃. Detailed measurements of the magnetic moment of the superconductor and ferromagnet as a function of temperature and magnetic field have been performed using SQUID magnetometry. Magnetometry and relaxation measurements show that the modification of the superconducting properties of YBCO strongly depends on the interaction with the ferromagnetic layer on top. The barrier layer has a significant impact on both the supercon-ducting properties of the YBCO film and the ferromagnetic ordering of CaRuO₃. The physical properties mentioned above were discussed in correlation with the materials’ structure determined by XRD analysis. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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11 pages, 2563 KiB

Open AccessArticle

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe_0.5Te_0.5 Superconductor

by Masood Rauf Khan, Antonio Leo, Angela Nigro, Armando Galluzzi, Massimiliano Polichetti, Valeria Braccini, Matteo Cialone, Mario Scuderi and Gaia Grimaldi

Materials 2021, 14(18), 5289; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185289 - 14 Sep 2021

Cited by 1 | Viewed by 1831

Abstract

The role of a layered structure in superconducting pinning properties is still at a debate. The effects of the vortex shape, which can assume for example a staircase form, could influence the interplay with extrinsic pinning coming from the specific defects of the material, thus inducing an effective magnetic field dependence. To enlighten this role, we analysed the angular dependence of flux pinning energy U(H,θ) as a function of magnetic field in FeSe_0.5Te_0.5 thin film by considering the field components along the ab-plane of the crystal structure and the c-axis direction. U(H,θ) has been evaluated from magneto-resistivity measurements acquired at different orientations between the applied field up to 16 T and FeSe_0.5Te_0.5 thin films grown on a CaF₂ substrate. We observed that the U(H,θ) shows an anisotropic trend as a function of both the intensity and the direction of the applied field. Such a behaviour can be correlated to the presence of extended defects elongated in the ab-planes, thus mimicking a layered superconductor, as we observed in the microstructure of the compound. The comparison of FeSe_0.5Te_0.5 with other superconducting materials provides a more general understanding on the flux pinning energy in layered superconductors. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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20 pages, 3305 KiB

Open AccessArticle

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa₂Fe₄As₄F₂

by Sunseng Pyon, Soichi Taya, Yuto Kobayashi, Ayumu Takahashi, Wenjie Li, Toshihiro Taen, Teng Wang, Gang Mu, Hisashi Kitamura, Ataru Ichinose and Tsuyoshi Tamegai

Materials 2021, 14(18), 5283; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185283 - 14 Sep 2021

Cited by 2 | Viewed by 1928

Abstract

We report the critical current density (J_c) and vortex pinning properties in single crystals of a novel iron-based superconductor (IBS) KCa₂Fe₄As₄F₂ with large J_c in the pristine state, before and after introduction of artificial defects by swift-particle irradiation. The effects of 2.6 GeV U and 3 MeV proton irradiations in KCa₂Fe₄As₄F₂ single crystals on transition temperature T_c and J_c, including its dose dependence, are systematically studied. J_c~8 MA/cm² under a self-field at 2 K in the pristine crystal is strongly enhanced up to 19.4 and 17.5 MA/cm² by irradiation of 2.6 GeV U-ions and 3 MeV protons, respectively. Suppression of T_c and dose dependence of J_c in KCa₂Fe₄As₄F₂ is different from that in a representative IBS of (Ba,K)Fe₂As₂, which can be explained by considering the presence of embedded defects in pristine KCa₂Fe₄As₄F₂. The vortex dynamics in the pristine and proton irradiated KCa₂Fe₄As₄F₂ single crystals are also investigated from the analyses of the field dependence of J_c and the normalized magnetic relaxation rate. In addition to the contribution of embedded defects, weak collective pinning is considered for comprehensive analyses. Vortex dynamics in KCa₂Fe₄As₄F₂ is similar to those in (Ba,K)Fe₂As₂ to some extent, and different from that in anisotropic Li_0.8Fe_0.2OHFeSe. Large anisotropy, due to the presence of insulating blocking layers in KCa₂Fe₄As₄F₂, which leads to much lower irreversibility field (H_irr) compared with 122-type IBSs, strongly affect the vortex dynamics. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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12 pages, 2004 KiB

Open AccessFeature PaperArticle

High Pinning Force Values of a Fe(Se, Te) Single Crystal Presenting a Second Magnetization Peak Phenomenon

by Armando Galluzzi, Krastyo Buchkov, Vihren Tomov, Elena Nazarova, Antonio Leo, Gaia Grimaldi and Massimiliano Polichetti

Materials 2021, 14(18), 5214; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185214 - 10 Sep 2021

Cited by 9 | Viewed by 1721

Abstract

The magnetization M of an Fe(Se, Te) single crystal has been measured as a function of temperature T and dc magnetic field H. The sample properties have been analyzed in the case of a magnetic field parallel to its largest face H||ab. From the M(T) measurement, the T_c of the sample and a magnetic background have been revealed. The superconducting hysteresis loops M(H) were between 2.5 K and 15 K showing a tilt due to the presence of a magnetic signal measured at T > T_c. From the M(H) curves, the critical current density J_c(H) has been extracted at different temperatures showing the presence of a second magnetization peak phenomenon. By extracting and fitting the J_c(T) curves at different fields, a pinning regime crossover has been identified and shown to be responsible for the origin of the second magnetization peak phenomenon. Then, the different kinds of pinning centers of the sample were investigated by means of Dew-Hughes analysis, showing that the pinning mechanism in the sample can be described in the framework of the collective pinning theory. Finally, the values of the pinning force density have been calculated at different temperatures and compared with the literature in order to understand if the sample is promising for high-current and high-power applications. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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27 pages, 15038 KiB

Open AccessArticle

Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, n-Value, and Engineering Critical Current Density in MgB₂ Wires

by Daniel Gajda, Andrzej J. Zaleski, Andrzej Morawski, Małgorzata Małecka, Mustafa Akdoğan, Firat Karaboğa, Doğan Avcı, Hakan Yetiş, Ibrahim Belenli and Tomasz Czujko

Materials 2021, 14(13), 3600; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14133600 - 28 Jun 2021

Cited by 2 | Viewed by 1793

Abstract

Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (B_irr), critical temperature (T_c), upper magnetic field (B_c2), engineered critical current density (J_ec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on B_irr, T_c, B_c2, J_ec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest B_irr, T_c, B_c2, J_ec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB₂. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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17 pages, 1057 KiB

Open AccessArticle

Effect of Controlled Artificial Disorder on the Magnetic Properties of EuFe₂(As_1−xP_x)₂ Ferromagnetic Superconductor

by Sunil Ghimire, Marcin Kończykowski, Kyuil Cho, Makariy A. Tanatar, Daniele Torsello, Ivan S. Veshchunov, Tsuyoshi Tamegai, Gianluca Ghigo and Ruslan Prozorov

Materials 2021, 14(12), 3267; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14123267 - 13 Jun 2021

Cited by 4 | Viewed by 1999

Abstract

Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor,

{EuFe}_{2} {({As}_{1 - x} P_{x})}_{2}

(x = 0.23), were measured in pristine state and after different [...] Read more.

Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor,

{EuFe}_{2} {({As}_{1 - x} 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,

T_{c} (H)

, shows an extraordinarily large decrease. It starts at

T_{c} (H = 0) \approx 24 K

in the pristine sample for both AC and DC measurements, but moves to almost half of that value after moderate irradiation dose. Remarkably, after the irradiation not only

T_{c}

moves significantly below the FM transition, its values differ drastically for measurements at different frequencies, ≈16 K in AC measurements and ≈12 K in a DC regime. We attribute such a large difference in

T_{c}

to the appearance of the spontaneous internal magnetic field below the FM transition, so that the superconductivity develops directly into the mixed spontaneous vortex-antivortex state where the onset of diamagnetism is known to be frequency-dependent. We also examined the response to the applied DC magnetic fields and studied the annealing of irradiated samples, which almost completely restores the superconducting transition. Overall, our results suggest that in

{EuFe}_{2} {({As}_{1 - x} P_{x})}_{2}

superconductivity is affected by local-moment ferromagnetism mostly via the spontaneous internal magnetic fields induced by the FM subsystem. Another mechanism is revealed upon irradiation where magnetic defects created in ordered

{Eu}^{2 +}

lattice act as efficient pairbreakers leading to a significant

T_{c}

reduction upon irradiation compared to other 122 compounds. On the other hand, the exchange interactions seem to be weakly screened by the superconducting phase leading to a modest increase of

T_{m}

(less than 1 K) after the irradiation drives

T_{c}

to below

T_{m}

. Our results suggest that FM and SC phases coexist microscopically in the same volume. Full article

(This article belongs to the Special Issue Synthesis, Design, Characterization of Unconventional Superconducting Materials)

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