Journal of Superconductivity and Novel Magnetism最新文献

Rapid annealing of in-situ Fe/Mg + 2B tapes using laser technologies with a n-IR emitting fiber laser with pulse durations up to 200 ns and pulse repetition frequencies up to 1.4 MHz is reported. The relevant parameters involved in the laser treatment, such as laser power, pulse duration, repetition frequency, laser scanning speed and treatment repetitions are considered to control the annealing process. Two different configurations were used to scan the conductor: laser beam scanning and laser line scanning. The results are compared with conventional annealing performed in furnace. The tapes annealed using both conventional furnace and laser exhibited normal-state resistivity values in the range of 7–10 µΩ, superconducting transition temperatures between 37 and 38 K, and similar engineering critical current densities of approximately 20 A/cm² at 5 T and 25 K. A simplified 2D numerical model of experimental laser treatment is presented. This model solves the heat conduction equation including heat convection, radiation, and evaporation flux using COMSOL Multiphysics software for numerical simulations. The flow coupled heat transfer module is used to study the temperature distribution inside the two-dimensional iron sheath. Surface tension, buoyancy, recoil pressure and thermocapillary force are also considered in the calculations.

Nanoparticles containing metallic cobalt, cobalt oxides CoO, Co₃O₄, cobalt carbide Co₂C, and combinations of these materials were synthesized via thermal decomposition of a solution of oleic acid, oleylamine, and cobalt acetate under various conditions. A carbon shell formed on the surface of the nanoparticles directly during the decomposition process. X-ray diffraction with Rietveld refinement and transmitted electron microscopy were used to determine the structure, phase composition, morphology, and size of the nanoparticles. Raman spectroscopy confirmed the formation of a carbon shell around the nanoparticles under all decomposition conditions. Field and temperature dependences of magnetization allowed us to establish the core-shell structure of the nanoparticles. For all types of synthesized nanoparticles, a shift in the hysteresis loops due to exchange interaction was observed, and the magnitude of the exchange anisotropy field was estimated. The spectrum of magnetic circular dichroism was shown to be described by curves similar in shape to that characteristic of metallic cobalt, but shifted along the axis of light wave energy depending on the phase composition.

The results of measurements of the transverse voltage in the Hall configuration, 𝑈_𝑦, under conditions of motion of the charge and vortex subsystems in orthogonal magnetic and electric fields on epitaxial films of the layered high-temperature superconductor Nd_2-xCe_xCuO₄ are presented. The motion of Josephson vortices across CuO₂ layers (along the c-axis) is analyzed considering the effects of intrinsic pinning. An exponential dependence of critical depinning current 𝑗_𝑐 (𝐵) for Josephson vortices is established in contrast to the power law dependences for Abrikosov vortices. With increasing external magnetic field after the depinning by a magnetic field at B = B_c, the onset of the vortex creep regime, which evolves into the flux-flow regime at crossover field B = B_f, is observed.

This work investigates the structural, magnetic, electrical, and dielectric properties of the multi-element A-site substituted perovskite La₀.₅₇Nd₀.₁₀Sr₀.₁₈Ag₀.₁₅CrO₃ (LNSACrO) synthesized by the sol–gel method. X-ray diffraction and Rietveld refinement confirm a rhombohedral structure with the R-3c space group. Raman and SEM analyses reveal lattice distortion and a polycrystalline microstructure. Magnetic measurements performed under 0.05 T show a complex magnetic behavior, with an antiferromagnetic transition at TN = 12 K and a ferromagnetic–paramagnetic transition at TC = 275 K, highlighting the influence of multi-cation A-site substitution on the magnetic ordering. Electrical measurements reveal thermally activated conduction with an activation energy of 0.280 eV, while the temperature dependence of the Jonscher exponent indicates a correlated barrier hopping (CBH) mechanism. Impedance analysis confirms non-Debye relaxation and distinct grain and grain-boundary contributions. These results demonstrate the strong coupling between A-site chemical disorder and the magnetic and electrical properties of LNSACrO, highlighting its potential for multifunctional magneto-dielectric and electronic applications.

This study presents a comprehensive magneto-thermal analysis of a ferrimagnetic hexagonal nanotube with a core-shell structure. The system consists of a core with a spin-3/2 and a shell with a spin-2. Using both the Mean-Field Approximation (MFA) and Monte Carlo Simulations (MCS), we investigate the system’s magnetic properties, phase diagrams, and hysteresis behavior. Our findings reveal complex thermal phenomena, including first- and second-order phase transitions, as well as single and multiple compensation temperatures. The phase diagrams illustrate the influence of key parameters, such as the exchange coupling interactions, the external magnetic field, and the crystal field, on the critical and compensation temperatures. Furthermore, the hysteresis loops demonstrate rich magnetic behavior, showing multi-loop patterns that are sensitive to both temperature and external magnetic field. The use of both theoretical methods provides a robust understanding of this system, highlighting the crucial role of geometric confinement and mixed-spin configurations in creating tunable magnetic properties for potential spintronic applications.

This study investigates spin-wave propagation and coupling dynamics in a magnonic architecture comprising orthogonally arranged thin-film ferrite waveguides. By numerically solving the Landau–Lifshitz–Gilbert equation, we establish a steady-state spin-wave transport regime and reconstruct spatial distributions of the internal magnetic field and the out-of-plane dynamic magnetization component under in-plane static bias fields. Analysis of the amplitude–frequency characteristics reveals how reorienting the external magnetic field selectively excites distinct frequency bands, enabling controlled spin-wave routing at the circuit outputs. Leveraging this field-tunable spin-wave interference and coupling mechanism, we propose a reconfigurable magnonic logic architecture capable of emulating fifteen fundamental logic operations. These findings advance the development of field-programmable magnonic circuits and contribute to the broader field of novel magnetic materials and spin-wave-based information processing.

We report a method to locally modify superconducting materials using nano-laser direct writing, rather than conventional ablation or etching, for the fabrication of constriction-type Josephson junctions and superconducting quantum devices. Specifically, at a fixed laser power of 120 mW, the critical current (I_c) can be modified from 250 (mu )A to 80 (mu )A by increasing the pulse width from 3.0 ms to 4.0 ms, establishing an optimal processing window prior to the onset of irreversible film degradation. The optimized SQUID operated at 4.0 K exhibited a voltage-flux modulation depth of approximately 200 (mu )V, a maximum flux-to-voltage transfer coefficient (V_{varPhi }) of 0.75 mV/(varPhi _0), and a white flux noise spectral density of 2 (mu varPhi _0) Hz(^{-1/2}). With its ability to locally modify superconducting properties without material removal, this approach opens new avenues for in-situ tunable Josephson junctions and provides a flexible platform for future superconducting quantum circuits.

Nanocrystalline BiFeO₃ with a tunable average crystallite size ranging from 40 to 150 nm were synthesized using sucrose-assisted solution combustion method. Control of crystallite size was achieved through two routes: sequential heat treatment of combustion product and variation of the sucrose-to-oxidizer ratio in the initial compositions. The magnetic characteristics revealed a noticeable dependence on the chemical prehistory. For the heat-treated series, the size-dependent evolution of saturation magnetization at 300 K follows a modified core-shell magnetization model. The samples synthesized by varying sucrose-to-oxidizer ratio demonstrated an exponential magnetization decay with crystallite size. These findings establish a dual-route physiochemical strategy for tailoring the magnetic functionalities of orthoferrite nanocrystals for advanced spintronic and magnetocatalytic applications.

In this study, the effects of CdCl₂ doping on the structural, mechanical, and superconducting transition behavior of MgB₂ superconductors were investigated. MgB₂ samples containing 0, 3, 5, and 10 wt% CdCl₂ were synthesized by the conventional solid-state reaction method. Structural characterization was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the superconducting transition behavior was evaluated by temperature-dependent electrical resistivity (R–T) measurements. Mechanical properties were investigated by the Vickers microhardness method and analyzed using Meyer’s law, the proportional specimen resistance (PSR), elastic/plastic deformation (EPD), and Hays–Kendall (HK) models. Quantitative grain-size analysis using Fiji/ImageJ revealed a systematic increase in the mean Feret diameter from 0.273 ± 0.037 μm for the undoped sample to 2.792 ± 0.623 μm for the 10 wt% CdCl₂-doped sample, accompanied by a progressive shift of the grain-size distribution toward larger sizes. These results provide quantitative evidence for grain coarsening induced by CdCl₂ addition. The superconducting transition temperature decreased with increasing dopant content, together with changes in the transition width. Microhardness measurements exhibited a pronounced reverse indentation size effect (RISE), and the hardness enhancement was associated with grain coarsening and microstructural densification suggested by the quantitative ImageJ analysis and SEM observations. Among the evaluated models, Meyer’s law showed the best agreement with the experimental data. Overall, CdCl₂ addition enhanced the mechanical response of MgB₂ while modifying its superconducting transition behavior.