Springer Science and Business Media LLC

High-temperature superconducting (HTS) maglev, named as the most promising technology of the future transportation, has attracted more and more attention, especially on the dynamic characteristics. In practice, the temperature varying inside the bulk together with the irregularity of the permanent magnetic guideway (PMG) directly and simultaneously affects the levitation and guidance force. This paper takes the HTS bulk, liquid nitrogen (LN), and PMG into account to establish the two-dimensional magnetic-thermal-guideway coupled model by using COMSOL Multiphysics. In order to simulate the magnetic field fluctuation caused by the PMG’s arrangement irregularity, we add the test track irregularity spectrum of high-speed railway to the PMG. The temperature effect on levitation and guidance force is simulated and analyzed under four conditions of excitations as well as comparing with the model without considering the temperature. The results show that the temperature and coupling of excitations in both directions simultaneously affects the magnitude of levitation and guidance force, and the difference caused by above two factors is significant, which makes a better understanding of the relation between the force and temperature and provides an effective reference for the HTS bulk’s dynamic analysis.

Magnetoresistance (MR) was measured in a La1.48Nd0.4Sr0.12CuO4 single crystal in perpendicular magnetic fields H up to 9 T in the region of the structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase. The hysteretic MR exhibits discrete jumps or avalanches only when the transition is approached from the LTT phase, and only during the first field sweep. The properties of the hysteresis are found to be independent of the field driving rate. The results are consistent with the presence of magnetostructural domains coupled with the charge degrees of freedom.

Nanocrystalline samples of both undoped TiO2 and with 5 at.% Co at cationic sites were prepared by a simple chemical route. X-ray diffraction study of these samples revealed an increase in lattice parameters due to incorporation of Co in the TiO2 lattice and possibly due to formation of oxygen vacancies. No traces of crystalline Co or any other secondary phases could be detected. High-temperature SQUID measurement of these samples exhibited ferromagnetic signature up to 700 K, implying that the Curie temperature of doped and undoped TiO2 exceeds 700 K. Vacuum annealing of both types of samples enhanced the ferromagnetic character. The as-prepared and vacuum-annealed Co incorporated TiO2 samples, in addition to the ferromagnetic character, also exhibited a paramagnetic signal. All these measurements strongly support the role of defects in inducing room-temperature ferromagnetism in undoped and Co doped TiO2 nanopowders, which can be explained using the bound magnetic polaron model.

An overview of superconductivity in the rare-earth nickel borocarbides (RNi2B2C, where R represents a rare earth element or Y) is presented, with an emphasis on the interplay between magnetism and superconductivity in general and the behavior of the nonmagnetic superconductors YNi2B2C and LuNi2B2C, in particular. Some open questions are identified.

In metallic magnets with a low carrier density, scattering from magnetic fluctuations above and near the transition temperature T c provides a large contribution to the electrical resistance. Because the fluctuations can be suppressed by a magnetic field, a large negative magnetoresistance ensues. In a simple model, we find the low field magnetoresistance scales with the ratio of field induced magnetization m(H) to the saturation magnetization m sat: Δρ/ρ=(ρ(T, 0)−ρ(T, H))/ρ(T, 0)≈C(m/m sat)2. At very low carrier densities magnetic polarons should form in a range of temperatures above T c. The CMR perovskite manganites cannot be explained without strong coupling of the magnetic order to lattice distortions (of the Jahn–Teller type) above T c.

Nd-Fe-B gel was prepared by employing the precursors of chloride-based metal salts including NdCl3⋅6H2O, FeCl3⋅6H2O, H3BO3, citric acid, and ethylene glycol. Mixed oxide powders were fabricated by subsequent annealing. The oxide powders were reduced at 800 °C in Ar + H2 atmosphere for different times (2, 5, 10, 15, and 24 h) to prepare Nd2Fe14B nanoparticles. The role of reduction time in phase, morphologies, microstructure, and magnetic properties of the final powders was investigated by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM) techniques, respectively. The results show that the Nd2Fe14B phase was formed successfully at higher reduction times (15 and 24 h), and the average size of reduction-treated products was less than 220 nm. The magnetic properties were fluctuated with an increase in reduction time at a reduction temperature of 800 °C. The samples reduced for 15 h had a maximum coercivity of 1873 Oe, and the samples reduced for 24 h had a maximum saturation magnetization of 118.52 emu/g. A maximum squareness ratio of 0.64 was obtained by reduction for 24 h. The results show that the reduction-diffusion process at 800 °C was done successfully in higher reduction times.

In this work, Co–TiO2 metallic composite films with a novel nanostructure have been electrodeposited in potentiostatic regime onto copper substrates, from a solution based on cobalt sulfate containing suspended TiO2 nanoparticles, with magnetic stirring of the electrolyte. The effect of deposited film thickness on the morphology, microstructure, and composition of the films was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Functional properties (magnetic and electronic transport) of films with different thicknesses were studied in a view to find out the possibility for some technological applications. Nanocomposite Co–TiO2 films contain three main phases: hcp Co crystalline grains (9–10 nm average size), TiO2 nanoparticles (28 nm average diameter) embedded in Co metallic matrix and Co(OH)2 adsorbed on the crystallite frontiers. The films display hysteresis (coercive field of 7.8÷11.9 kA/m) and significant values of magnetoresistance (with a maximum of −59 % in the case of 0.07 μm film thickness). These properties can be qualitatively explained both by the elastic spin-dependent scattering of the conduction electrons at the interface between the magnetic Co matrix grains and the nonmagnetic regions, and by occurrence of antiferromagnetic coupling between Co crystallites, favored by inclusion in film of TiO2 nanoparticles.

Photonic crystals containing graphene nanolayers have been attracting increasing attention due to their distinctive properties. In this paper, we present a theoretical analysis on the transmission properties of magneto-photonic crystals containing graphene nanolayers by using the transfer matrix method. The investigation shows that unidirectional defect modes with high transmittance can be achieved in the proposed structure, and broad flat-top photonic conduction bands (PCBs) can also be found between the graphene-induced photonic band gap and the Bragg gap. Furthermore, the study on the PCBs indicates that the relationship between the number of PCBs (n) and the period number of the structure (N) can be expressed as n = N − 1(N = 2,3,4…). And, new and unexpected photonic band gaps among PCBs are observed. The effects of chemical potential of graphene, thickness of defect layer, and incident angle on transmission properties are also discussed. The research results may provide a valuable reference for the design and fabrication of optical communication devices, such as isolators, switches, multichannel filters, and so on.

Magnetic and electronic structures of K1-xFe2Se2 (x = 0.0, 0.2, 0.4, 0.6, and 0.8) in collinear antiferromagnetic state were studied by first-principles calculations. With the increase of K vacancy concentration, the magnetic moment and Fe-Se bond length were decreased (from x = 0.0 to 0.6) first and then increased (from x = 0.6 to 0.8). When the K vacancy concentration was 0.6 (that is K0.4Fe2Se2), the magnetic moment was completely suppressed, and the Fe-Se bond was the smallest. In contrast, the hybridized band width (HBW) first increased and then decreased, reaching to the maximum for K0.4Fe2Se2. The electron Fermi surface shrank gradually and the hole Fermi surface grew. The calculated results explained why experimental K0.8Fe2Se2 showed superconductivity compared with KFe2Se2.