Journal of Superconductivity and Novel Magnetism最新文献

The transport and magnetic properties of the Magnéli phase tungsten oxide WO_2.90, prepared via spark plasma sintering, were investigated across a broad temperature range of 4–550 K, including the previously unexplored low-temperature region below 300 K. Microstructure analysis shows that obtained pellets are fully dense, enabling reliable measurement of transport properties. Resistivity measurements reveal typical metallic behavior of WO_2.90 at low temperatures. Above room temperature, resistivity tends to saturate by reaching a maximum value near 430 K. The resistivity saturation indicates that Mott-Ioffe-Regel limit is approached, where the charge carrier mean free path becomes comparable to the interatomic spacing. The temperature dependence of the resistivity can be well described by the phenomenological parallel resistor model. Significant positive magnetoresistance was observed at low temperatures, with an unusual linear dependence on the magnetic field. Despite its metallic conductivity, WO_2.90 displays weak diamagnetism, likely due to the substantial core diamagnetism of tungsten and the bipolaronic pairing of charge carriers.

In electronic models on lattices with strong geometric frustration (flat band models), the band dispersion of electrons can vanish, resulting in what is known as a flat band. Flat bands are known to serve as a platform for the emergence of various intriguing physical properties. Realizing flat bands in actual materials, however, remains a challenging task. In this paper, we report that the flat band model approximately holds in the pyrochlore oxide Pb(_2)Bi(_2)O(_7), as demonstrated by first-principles calculations. Furthermore, we propose that, among the two key parameters in flat band systems—the flat band width and the carrier density—the latter can be selectively controlled, approximately, by utilizing the solid solution Pb(_2)(Sb,Bi)(_2)O(_7). This finding represents a new step toward “flatronics,” a field focused on controlling flat band systems.

The RTX (where R represents rare earth, T represents 3d/4d/5d transition metal, and X represents p-block element) series comprises an extensive collection of equiatomic (1:1:1) intermetallic compounds that exhibit diverse crystal and magnetic structures with their vast array of physical properties, which includes field-induced phase transitions, commensurate, incommensurate, superconductivity, non-trivial topology, etc. In the present work, the exchange interactions and phonon topology of EuAuAs, GdAuGe, and GdAgGe have been discussed. By correlating the spin configurations to the underlying Heisenberg spin model, we have successfully estimated the exchange interactions. Furthermore, by using the mean-field approximation, the Neel temperatures of rare-earth compounds have been reported, which is consistent with the experimental value. The phonon dispersion of EuAuAs and GdAuGe exhibits non-trivial topological phononic states with nodal surfaces and Dirac points on the (k_z) = (pi ) plane. The calculated phonon spectrum of GdAgGe reveals the presence of a nodal line along the (k_z) = (pi ) plane. The exploration of phonon topology opens up a new pathway toward comprehending and harnessing the exotic physical characteristics exhibited by these rare-earth compounds and other analogous quantum materials.

Pr_0.9Sr_0.1MnO₃ was synthesized using the solid-solid method, and its structural and magnetic characteristics were thoroughly examined. The synthesis procedure was meticulously detailed. In the initial phase, structural analysis was conducted employing X-ray diffractometry with copper radiation, alongside magnetization measurements. Magnetic properties were investigated utilizing the BS1 magnetometer, facilitating a comprehensive understanding of the material's behavior. Subsequently, in the second phase, Monte Carlo simulations were employed to explore the magnetic characteristics and magnetocaloric effects of the Pr_0.9Sr_0.1MnO₃ perovskite. This approach provided insights into thermal magnetization, magnetic susceptibility, magnetic entropy changes, relative power cooling, and magnetic hysteresis cycles.

Permanent-magnet electro-dynamic suspension (PMs-EDS) maglev systems are shaping the future of modern transport by providing high-speed, energy-efficient, and sustainable transport solutions. In this study, numerical simulations were performed to determine the optimum geometrical parameters of aluminum rail and permanent magnet arrangements for EDS systems. For that, the aluminum rail and permanent magnet combinations were investigated, and then the same simulations were repeated by creating cavities in the aluminum rails for cost efficiency. The highest levitation-to-drag ratio (LDR) was achieved with magnet arrays having a fill factor of 0.4, 20 mm thick aluminum, and an aluminum rail width of 60 mm. Additionally, by creating cavities into the rails, it was calculated that approximately $2.44 million could be saved from the total cost of $17.34 million cost of the 1000 km double-strip aluminum rails, with negligible reduction in the LDR ratio. The findings of this study provide a sustainable and economical transport solution by increasing the cost effectiveness of PMs-EDS maglev systems. The results obtained may pave the way for the development of different types of applications of maglev technology and increase the potential for commercial use of maglev transport systems.

Recently, there has been a focus on the development of power devices using high-temperature superconductors (HTSs) such as superconducting cables, superconducting magnetic energy storage (SMES) systems, superconducting motors, and generators since no joule loss occurs during operation. HTS is said to replace LTS in fusion reactors. Second-generation (2G) HTS has a very thin tape-like composite layered structure. Before the design of devices made out of HTS tape, the electromechanical properties of HTS tape are required. One such property is the I-V characterization of tape under tensile strain. As tape undergoes a state of stress during operation, the knowledge of the degree of degradation of current carrying capacity due to this is of utmost importance. A test setup for I-V characterization under tensile strain is developed by modifying the existing universal testing machine (UTM). This cryogenic UTM (C-UTM) can test stress–strain and I-V characterization of YBCO-based 2G HTS tape under varying strain at 77 K. Experimental procedure and instrumentation are discussed. A SuperPower make 2G HTS tape was tested in this UTM, and the result is compared with the available literature and manufacturer data sheet. This setup will be very helpful for testing the new HTS tape model for which experimental data are not yet present in the literature. A scanning Hall probe microscopy (SHPM) was also utilized to obtain the critical current variation along the length of the deformed test HTS sample. The HTS tape has undergone complete degradation along its length as a result of the applied longitudinal strain.

In this study, we detail the KNbO₃:YBCO film deposition process using the pulsed laser deposition (PLD) technique and explore the influence of potassium niobate (KNbO₃) nanoparticles (NPs) on pinning characteristics of nanocomposite YBCO films. The XRD investigation confirms the orthorhombic phase of YBCO, and it remains consistent even when NPs are included in the nanocomposites. A Magnetic Property Measurement System (MPMS) is used to measure the magnetic characteristics, applying a field within a range of ± 7 T. The KNbO₃:YBCO nanocomposite thin films exhibit higher critical current (J_c) in comparison to YBCO films. Notably, the most substantial improvement, ~ 3.5-fold, in J_c and flux pinning properties is observed in 0.5 wt% KNbO₃:YBCO nanocomposite thin films. Furthermore, the investigation reveals that nanocomposite films display a slower rate of J_c decay with the increase of fields as compared to YBCO thin films, indicating improved pinning properties. The results indicate that introducing small KNbO₃ nanoparticles in YBCO matrix is an effective way to enhance the in-field performance of YBCO.

An approach to model the anisotropic behaviour of core losses in grain-oriented laminations that are used in advanced electrical machines and transformers is proposed in this work. Core losses are usually split into static hysteresis loss, classical eddy current loss, and excess loss. The static hysteresis and excess loss components exhibit strongly anisotropic behaviours which at low frequencies may be modelled using the orientation distribution function (ODF) approach. However, the anisotropic behaviour of core losses at higher frequencies is rarely addressed. Therefore, this work aims to offer a method to model the anisotropy of these losses for a wide range of frequencies. This work proposes a modified approach that uses the ODF and the Kondorsky law to compute the core losses accurately in any direction for a wide range of frequencies so that the losses due to different magnetisation processes can be studied separately. The paper also highlights possible causes behind the anisotropic behaviour of the excess loss. The proposed approach is also compared with the original ODF description for modelling the loss behaviour along arbitrary directions. The computed loss-frequency behaviour at different induction levels agrees with measured ones along arbitrary directions. The proposed formulation can be used to estimate the losses of transformers and rotating machines as a function of magnetic field direction and frequency.

We investigated the magnetic, thermodynamic, and transport properties of polycrystalline GdNiSi₃. The compound crystallized in an orthorhombic structure with the space group Cmmm. Heat capacity and magnetic measurements revealed bulk antiferromagnetic ordering at T_N = 22.5 K, θ_p = -25 K, and an effective magnetic moment of μ_eff = 8 μ_B/Gd. A metamagnetic transition occurred around 28 kOe in the magnetic isotherm at 3 K. Furthermore, resistivity measurements conducted under a magnetic field at 2 K displayed a low-temperature drop near 22.5 K, corresponding to the antiferromagnetic order.