Journal of Superconductivity and Novel Magnetism最新文献

The synthesis, structure, and magnetic properties of Ba₃REB₉O₁₈ (RE = Dy-Yb) compounds were investigated. Rietveld Refinement of the X-ray diffraction (XRD) data confirms that all compounds crystallize in a hexagonal Ba₃YB₉O₁₈-type structure with space group P6₃/m (No. 176) and Pearson symbol hP62. The lattice parameters a and c increase linearly with the increasing ionic radii of the RE³⁺ ions. RE³⁺ ions form two-dimensional triangular layers in the ab plane, which are separated by non-magnetic Ba/B-O polyhedra. The magnetic susceptibility measurement reveals no long-range magnetic order or spin glass behavior in any of the compounds above 2 K. The negative Curie-Weiss temperatures indicate dominant antiferromagnetic (AFM) exchange interactions between the RE³⁺ ions. The combination of triangular lattice and antiferromagnetic interaction suggests this family of compounds is a promising system for researching magnetic frustration.

Topological defects occurring in nonlinear classical field theories are described by a system of second-order differential equations. A breakthrough was made in 1976 by E. B. Bogomoln’yi who demonstrated that in several field theories these equations can be reduced to first-order provided the coupling constants take on particular values. One of the examples involved a string in the Abelian Higgs model which is equivalent to the Abrikosov flux line of the Ginzburg-Landau theory of superconductivity. In a similar vein, in the 1966 textbook Superconductivity of Metals and Alloys P. G. de Gennes explained how to reduce the second-order Ginzburg-Landau equations to first-order at a particular value of the Ginzburg-Landau parameter by a method due to G. Sarma. We analyze the two ways of arriving at the first-order Sarma-Bogomol’nyi equations and conclude that while they both rely on the same operator identity, Sarma’s method is free of the assumption that there is a topological defect. The implication is that Bogomol’nyi equations found in other field theories may be a source of a wider range of solutions beyond topological defects.

In order to develop submerged pumps to transfer liquid hydrogen, high temperature superconducting (HTS) motors to drive them as one of key components are a promising candidate with low electromagnetic loss and large specific power density per unit mass. However, since armature windings wound using HTS wires have a couple of problems such as three-phase unbalanced currents and frequency limitations, HTS wires are used only for rotor windings of the motors and metallic cables have to be applied to their armature windings. Therefore, numerical analyses to evaluate loss properties in multi-strand metal twisted cables for armature windings of HTS motors cooled at liquid hydrogen temperature are carried out by means of a two-dimensional finite element method. On the basis of a clarified physical mechanism of losses generated in the windings arranged within a slot of armature iron core, the obtained numerical results are also reproduced with theoretical expressions of the Joule loss for an alternating transport current and the eddy-current loss for an externally applied AC magnetic field. The influences of losses on the frequency and number of strands in metal twisted cables are investigated quantitatively.

The vortex dynamics for a high-performance BaZrO₃ doped (Y_0.5Gd_0.5)Ba₂Cu₃O_7-δ superconducting films are investigated by a dynamic magnetization-relaxation method. The superconducting films have dense columnar defects with density ~ 1.1×10¹¹ cm⁻². The dynamic relaxation rates exhibit a complex temperature dependence, indicating the presence of multiple magnetic vortex phase transitions and complex vortex-vortex interactions. Based on the experimental data, a vortex phase diagram has been constructed, which shows a large vortex elastic motion region suggesting strong flux pinning and potential applications of the REBCO films. There seems to be a vortex slush region under magnetic fields less than 2 T within the temperature range from 10 to 25 K. The investigation on the vortex pinning mechanisms indicates that δl-pinning takes the key role for the vortex motion in the present REBCO films. Based on the present results, it is believed that introducing strong δT_c-pinning into REBCO superconducting films is the key to further improving their performance at high temperatures and strong magnetic fields.

A new type of magnet called p-wave unconventional magnet is proposed, stimulated by the discovery of altermagnet. We study the tunneling conductance of p-wave unconventional magnet/superconductor junctions by adopting the effective Hamiltonian of p-wave unconventional magnets with time-reversal symmetry breaking, suggested (Hellenes et al. P-wave magnets, http://arxiv.org/abs/2309.016072024). The tunneling conductance shows an asymmetric behavior with respect to bias voltage in the helical p-wave superconductor junctions. It is caused by the missing of helical edge states contributing to the charge conductance owing to the momentum-dependent spin-split feature of the Fermi surface in p-wave unconventional magnets. In chiral d and p-wave superconductor junctions, the resulting spin-resolved tunneling conductance takes a different value for spin sectors due to the time-reversal symmetry breaking in superconductors. Our results qualitatively reproduce the results based on the simplified Hamiltonian (Maeda et al. J. Phys. Soc. Jpn. 93, 114703 2024), where only the odd function of the exchange coupling of p-wave unconventional magnets is taken into account, which gives the shift of the Fermi surface and preserves the time-reversal symmetry similar to the spin-orbit coupling.

In this paper, we investigate the interplay between disorder-induced localization and magneto-optical (MO) effects in one-dimensional magnetophotonic crystals (MPCs) composed of alternating Ce:YIG and GGG layers with randomized thicknesses. Using the transfer matrix method, we analyze the localization length and MO responses across polar, longitudinal, and transverse magnetic geometries for wavelengths inside and outside the photonic band gap (PBG). Our results reveal that disorder strength critically modulates localization: while it enhances transmission at PBG edges (consistent with), it suppresses MO effects in longitudinal/transverse geometries, contrasting with the polar case where nonreciprocal localization emerges for circular polarizations. Notably, in the polar geometry, disorder amplifies Faraday rotation. These findings align with recent studies on disorder-enhanced MO responses while demonstrating the tunability of localization via magnetic and structural parameters. The work provides design principles for disordered MPCs in applications such as optical isolation, sensors, and tuneable filters.

Magnetic measurements in different thermal-magnetic cycles were carried out on a SmBa₂Cu₃O_7-y single crystal with high critical current density. Two magnetization peaks were simultaneously observed on this strongly pinned sample in different thermal cycles. It was observed that a large and broad maximum on magnetization curves manifested only on a single magnetic field dependent magnetization M-H curve but not on a single zero-field cooling temperature dependent magnetization M-T curve, which was usually defined as fishtail effect (FE). The FE was an irreversible property mainly originated from strong pinning centers. On the other hand, the much smaller magnetization peak manifested only on field cooling M-T curves, which was reversible peak effect (PE). The PE took place at higher temperatures near vortex solid–liquid transition and may be caused by dense and weak pinning centers.

In this study, MgB₂ bulk superconductors doped with 0–20% wt SiC were synthesized via in‑situ Spark Plasma Sintering (SPS), and their physical and magnetic properties were systematically investigated. Resistivity–temperature (ρ–T) and H–T phase diagram analyses revealed that while increasing SiC content reduces the transition temperature (T_c) and broadens the transition width (ΔT_c), it simultaneously enhances flux pinning and magnetic stability through a dual mechanism. Specifically, partial decomposition of SiC at 850 °C leads to carbon substitution in the MgB₂ lattice, increasing electron scattering and creating effective lattice distortions, while residual SiC nanoparticles and Mg₂Si secondary phases act as volumetric and intergranular pinning centers. Critical current density (J_c) and normalized pinning force (F_p/F_p,max) analyses confirmed strong pinning performance, particularly at 10–15% wt doping levels, where both J_c and H_irr were maximized. Vertical and lateral levitation force measurements under zero‑field‑cooled (ZFC) and field‑cooled (FC) conditions further demonstrated that the 15% wt sample exhibited the most stable flux trapping capacity, maintaining strong magnetic response even near the superconducting transition. Notably, the sample with 5% wt SiC addition exhibited the highest critical current density of 1.08 × 10⁶ A/cm² at 20 K under self-field, confirming the effectiveness of optimized doping for high-performance applications.These results confirm that controlled SiC doping and SPS processing effectively tailor MgB₂ bulk superconductors for high‑performance magnetic and levitation applications.

In 1991, V. J. Emery in his important review article entitled “Some aspects of the theory of high temperature superconductors” (Emery, Phys. B: Condens. Matter. 169, 17–25 1991) argued against the Zhang-Rice reduction of three-band to an effective one-band model. In his words “...therefore it seems that the simple (t-J) model does not account for the properties of high temperature superconductors”. Over approximately 35 years after the initial debates much has happened in the field pertaining to this topic. Even though it is one of the most discussed issue, a comprehensive account and the required resolution are lacking. Connected to the debate over one-band versus three-band models is another discussion: the one-component versus two-component model for cuprates. The two-component model is most strongly advocated by Barzykin and Pines (Adv. Phys. 58, 1–65 2009). In this article the author attempts a perspective and a re-look on some of these issues. After an analysis of a large body of literature, author finds that V. J. Emery’s criticism of the Zhang-Rice reduction was correct. Many central experimental features of cuprates cannot be rationalized within the one-band model, and Johnston-Nakano scaling is one such example. Other examples are also discussed. Author introduces a simple-minded toy model to illustrate the core issues involved.

This study investigates the structural, optical, and magnetic properties of double perovskites (DP) structured Ba₂FeMnO₆ (BFMO) synthesized via the solid-state reaction method. Rietveld refinement of X-ray diffraction data confirms the formation of a cubic structure with space group Fm-3 m (#225) and high phase purity. Fourier Transform Infrared (FTIR) spectroscopy verifies the presence of metal–oxygen bonding. UV–Vis spectroscopy and Tauc plot analysis determine an optical band gap of 2.1 ± 0.01 eV. Magnetic measurements reveal room-temperature weak ferromagnetic (FM) behavior. These findings highlight BFMO's potential for room temperature spintronic applications.