Journal of Superconductivity and Novel Magnetism最新文献

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.

Development of wide band gap semiconductor with ferromagnetic properties over a wide temperature range is a long standing demand for their applications in multifunctional spintronic devices. We present ferromagnetic semiconductor properties in Al₂O₃ system, which is electrically an insulator and non-magnet, by modifying lattice structure and lattice defects in the process of non-magnetic Ga ion doping, Ag ion beam irradiation, and implantation of ferromagnetic (Fe, Co) metal ions in bulk and thin film samples. The samples in Rhombohedral structure (R (overline{3 }) c space group) were used for studying structural, electrical, optical and magnetic properties. X-ray photoelectron spectroscopy was used for information of the surface chemical state (elemental composition, chemical bonding, charge state of the ions, defects and vacancy) of the samples. The SRIM (Stopping and Range of Ions in Matter) calculations were used to estimate the ion-beam induced defects. The optical band gap values in the range of 3.6–4.5 eV confirmed wide band gap semiconductor nature of the samples. The ferromagnetic properties at room temperature were confirmed through magneto-optic Kerr effect (surface magnetic coercivity 530–850 Oe) and dc magnetic measurement (bulk magnetic coercivity 25–106 Oe and saturated magnetization 0.09–37 memu/g). The enhancement of ferromagnetic properties in Al₂O₃ based samples have been understood in terms of defect induced local spin order at the surface and bulk structure of the samples, activated during material synthesis.

We theoretically study the anomalous proximity effect in a clean normal metal/disordered normal metal/superconductor junction based on a Rashba semiconductor nanowire model. The system hosts two distinct phases: a trivial helical phase with zero-energy Andreev bound states and a topological phase with Majorana bound states. We analyze the local density of states and induced pair correlations at the edge of the normal metal region. We investigate their behavior under scalar onsite disorder and changing the superconductor and disordered region lengths in the trivial helical and topological phases. We find that both phases exhibit a zero-energy peak in the local density of states and spin-triplet pair correlations in the clean limit, which we attribute primarily to odd-frequency spin-triplet pairs. Disorder rapidly splits the zero-energy peak in the trivial helical phase regardless of the lengths of the superconductor and disordered normal regions. The zero-energy peak in the topological phase shows similar fragility when the superconductor region is short. However, for long superconductor regions, the zero-energy peak in the topological phase remains robust against disorder. In contrast, spin-singlet correlations are suppressed near zero energy in both phases. Our results highlight that the robustness of the zero-energy peak against scalar disorder, contingent on the superconductor region length, serves as a key indicator distinguishing trivial Andreev bound states from topological Majorana bound states.