Journal of Superconductivity and Novel Magnetism最新文献

We review recent progress in the study of transition metal dichalcogenide (TMD) superconductors—such as NbSe(_{2}) and TaS(_{2})—-in tunnel devices where the barrier is also a van der Waals material. Superconducting TMDs are of particular interest due to their lack of in-plane centrosymetry, leading to Ising superconductivity: conventional s-wave superconductivity where the internal spin axis of Cooper pairs is held out of plane by the Ising spin-orbit field. The devices reviewed are fabricated by placing ultrathin barriers—typically few-layer insulating TMDs—on top of an exfoliated superconductor and subsequent patterning of tunneling electrodes. This results in high-quality normal-insulator-superconductor (NIS) tunnel junctions, which enable the measurement of superconducting spectra with fine energy resolution, down to dilution refrigerator temperatures (below 100 mK). As reported by the authors and others, these spectra reveal intricate signatures of TMD physics from the bulk to the 2D limit. We report on studies showing the two-band superconducting character of (bulk) NbSe(_{2}), revealing different depairing processes in the two different NbSe(_{2}) bands. These two bands also appear in the spectral weight of vortex-bound subgap states. At high in-plane magnetic fields, many unconventional superconducting phases have been predicted, which are not necessarily mutually exclusive: triplet, orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO), striped FFLO, pair density wave, nematicity etc. We report on the spectral evolution of NbSe(_{2}) at high in-plane magnetic fields, which we interpret as evidence for odd-parity equal-spin triplet superconductivity. Finally, we present our vision for addressing these and other open questions with vdW tunneling devices.

Investigation of the influence of various carbon-based dopants, specifically carbon nanotubes (CNT), glutaric acid, melanin, boron carbide (B₄C), silicon carbide (SiC), and glucose, on the structural and superconducting properties of magnesium diboride (MgB₂) has been studied. The analysis conducted via X-ray diffraction (XRD) revealed modifications in peak positions, which can be attributed to lattice strain, with samples incorporated with melanin demonstrating the most pronounced alterations. This lattice strain led to a reduction in electron density within the σ hole band, consequently exerting a detrimental effect on superconductivity. Resistivity measurements indicate a reduction in the critical temperature (T_c) for all doped samples, with values ranging from 38.1 K (for pure) to 36.8 K (for melanin). Upon the assessment of critical current density (J_c), samples doped with SiC, CNT, glucose, and B₄C revealed significant enhancements at a magnetic field of 3 T (operating field of MRI). The highest J_c values were achieved at 7.2 × 10⁴ A/cm² at 5 K (CNT and GL) and 1.66 × 10⁴ A/cm² at 20 K for CNT. Collectively, the dopants CNT and SiC provided an optimal balance of lattice strain, grain connectivity, and flux pinning, leading to enhanced superconducting attributes across the comprehensive range of magnetic fields.

With the development of superconducting qubits, the demand for Josephson parametric devices is rapidly growing. However, effective tools for the design and simulation of such devices remain lacking. In this paper, we propose a unified approach for designing Josephson parametric devices. By constructing accurate models of superconducting quantum interference device (SQUID) in Keysight’s Advanced Design System (ADS) and utilizing harmonic balance (HB) analysis, we can simulate and design a range of Josephson parametric devices based on nonlinear mixing. The effectiveness of this approach is demonstrated through examples of Josephson parametric amplifiers and isolators. This method holds significant promise for the efficient design of Josephson parametric devices.

In order to obtain new materials with multifunctional properties, CaLaSnFeO₆ samples were synthesized by the solid reaction technique. Structural analysis was performed by X-ray diffraction technique. Rietveld refinement of the experimental data revealed that these materials crystallize in a perovskite-type monoclinic structure (P2₁/n, space group #14) with alternating arrangement of Fe-Sn cations along the three crystallographic axes. The strongly granular character of the surface of the material was observed by scanning electron microscopy micrographs. X-ray energy dispersive spectra exhibited a close correspondence of the composition of the samples with that expected from their stoichiometric formula. Magnetic characterization in the temperature regime 50 K < T < 325 K and applied fields up to 30 kOe suggests the occurrence of a ferromagnetic ordering with Curie temperature T_C = 204 K. Diffuse reflectance spectra revealed the semiconducting characteristic of the CaLaSnFeO₆ double perovskite with a bandgap of E_g = 2.33 eV. To establish the origin of the magnetic interactions, electronic structure calculations were performed in the vicinity of the Fermi level by means of the Density Functional Theory. These properties generate technological expectations in the spintronics industry for the production of information storage devices on magnetic media based on polarized spin currents such as spin valves and magnetic transistors.

In this work, we study the return current of tunnel Josephson junctions, when one of electrode is the single-band and another is the multi-band superconductors. It is shown that the behavior of the return current of such junctions is determined by the ratio of the supercurrent amplitudes of the different channels in current-phase relation.

In an effort to thoroughly investigate the manufacturing processes of central solenoid (CS) magnets for Tokamak devices, this study has designed and constructed a CS model magnet. The magnet is wound with a double-tape soldered conductor (DTC) and stainless steel tape, consisting of two double-pancake (DP) coils with 30 × 2 turns each. By optimizing the winding, joint, and insulation techniques, the magnet achieved a critical current of 269 A at 77 K. The inductance of the magnet is 9.4 mH. When the magnet is applied to a direct current (DC) with an amplitude of 200 A, the central magnetic field is 0.07 T. Given that alternating current (AC) loss is a significant issue in the design of CS magnets, leading to higher cooling costs, increased operational risks, and possible irreversible damage to superconducting devices, this paper primarily focuses on studying AC loss in the designed CS model magnet. Simulations were performed using the H-formulation, J-formulation, and T-A formulation models, and the AC loss of the magnet was experimentally measured using the electrical method. The experimental results revealed that the AC loss for the CS model magnet was 5.1 J. Among the simulation models, the H-formulation model provided results closest to the actual values, with a significant increase in computational efficiency achieved by employing a homogenized method. This paper conducts a detailed comparative analysis of the characteristics and applicability of these three simulation models and investigates the effects of the AC cycle, current amplitude, and charging rate on AC loss through experimental studies. Ultimately, we designed and applied a current to the CS model magnet that matched the charging rate in the CS magnet within the tokamak device and found that the AC loss was the greatest during the plasma breakdown process.

Two-dimensional materials with intrinsic magnetic properties are expected to be crucial for future spintronic devices and magnetic memory devices, which are easy to exfoliate and maintain magnetic properties for extended periods, spanning from several layers down to single-molecule layers. In this work, the electronic structures and magnetic properties of two-dimensional CrAl(_2)S(_3)Cl(_3) were studied by first-principles calculations using the density functional theory within the generalized gradient approximation with non-collinear magnetic structure calculations. Calculated results indicate that CrAl(_2)S(_3)Cl(_3) exhibits Néel antiferromagnetic behavior, with an indirect bandgap of 1.21 eV, demonstrating an excellent structural stability. The Néel antiferromagnetic behavior originates from direct exchange interactions generated by the d electrons of Cr. The phase transition temperature of CrAl(_2)S(_3)Cl(_3) is around 58.5 K estimated by Monte Carlo simulations within Heisenberg model. Our investigation demonstrates that two-dimensional CrAl(_2)S(_3)Cl(_3) may be a promising candidate in the field of optoelectronics and provides theoretical guidance for exploring two-dimensional semiconductors.

The study explores the exciting development of nanoferrite systems designed for magnetic hyperthermia applications. Nanoparticles with the formula Co_1-xCu_xFe₂O₄ (x = 0.00–0.20 in increments of 0.04) were synthesized through the sol–gel method, utilizing polyvinyl alcohol as a chelating agent to facilitate precise control over particle size. The as-prepared powders were annealed at 400 ℃, 600 ℃, and 800 ℃ to examine the influence of annealing temperature on the development of domains and size-dependent magnetic properties. Structural analysis using X-ray diffraction and transmission electron microscopy revealed well-crystalline spinel structures, with particle sizes ranging from 5.6 to 8 nm for samples annealed at 600 ℃, consistent with the crystallite sizes (from 5.5 to 8 nm) estimated from Williamson-Hall plots. At room temperature, the specific magnetization of pristine cobalt ferrite, measured under a maximum applied magnetic field of 20 kOe, showed a significant increase from 10 emu/g to 69.1 emu/g with the increase in annealing temperature from 400 to 800 ℃. The observed increase in coercivity (H_c) with annealing up to 600 ℃ is linked to crystal growth within the single domain region, whereas the subsequent decrease in H_c at 800 ℃ is associated with the transition of particles to a multidomain state. The single domain nanoparticles, prepared by annealing at 400 ℃, with low coercivity and moderate magnetization were coated with chitosan and subjected to induction heating experiments. The coercivity of the coated nanoparticles was significantly lower compared to the uncoated nanoparticles. Among the compositions, Co_0.88Cu_0.12Fe₂O₄ exhibited superior performance, demonstrating long-term water stability and the achieved high specific absorption rate (224 W/g) and intrinsic loss power (0.89 nHm²/kg) indicating that it would be an excellent candidate as a heating agent for magnetic hyperthermia applications.

Graphical abstract

Ternary La(Fe_1-xSi_x)₁₃ compounds undergo a first-order magnetic transition at the Curie temperature T_C. Above T_C, the compounds exhibit the itinerant electron metamagnetism. We have studied Hall effect and thermal conductivity of La(Fe_1-xSi_x)₁₃. The Hall resistivity was measured as a function of the magnetic field B at various temperatures. Using the magnetization data, we separated the normal Hall effect (NHE) and the anomalous Hall effect (AHE) in the ferromagnetic state. It is found that NHE is positive at low temperatures, while it becomes negative near T_C. The large AHE was observed for x = 0.12. Our analyses revealed that the skew scattering is dominant in the AHE. The temperature dependence of thermal conductivity λ exhibits a peak at T_C for x = 0.12 and 0.14, while abrupt reduction in λ was observed at T_C for x = 0.10 both on cooling and on heating. We discuss the physical origins of these anomalies in the transport properties of La(Fe_1-xSi_x)₁₃.

Quasi-static hysteresis loops of assemblies of magnetosome chains of various geometric configurations have been calculated using numerical simulation. A detailed comparison is carried out of the quasi-static hysteresis loops of assemblies of single and double magnetosome chains, as well as assemblies of flux-close rings. It was shown that the hysteresis loops of the studied assemblies differ significantly from each other and from the hysteresis loop of a random assembly of non-interacting spherical magnetite nanoparticles. Therefore, the presence of biogenic magnetite in natural samples of weakly magnetized ancient rocks and ocean sediments can, in principle, be detected from standard measurement of the quasi-static hysteresis loops of the sample under study.