Journal of Superconductivity and Novel Magnetism最新文献

Doping transition metal elements, including Ag, to replace Fe atoms is an effective means to control the superconducting properties of iron-based superconducting materials. In this study, crystalline samples of Fe(Se_0.4Te_0.6) with Ag content below 1% relative to Fe were prepared using a self-flux method, and two choices of dopant, elemental Ag and Ag₂O, were tested. Structural characterization and morphology analysis revealed that in samples directly doped with elemental Ag, Ag may not replace the original atoms in Fe(Se,Te) but is more likely to enter the interlayer gaps. Critical current density (J_c) extracted from magnetic measurements showed an enhancement in the superconducting properties, particularly the critical current density, of these samples. Conversely, doping with Ag₂O possibly led to the incorporation of dopants into the original lattice, resulting in a decrease in superconducting performance. The research comparing the behavior differences of different dopants provides an important reference for subsequent studies in this field.

The microwave propagation characteristics of the superconducting coplanar waveguide structure that incorporated a ferroelectric thin film were theoretically studied by utilizing the spectral domain method. Tunability of the transmission characteristics was introduced by the inclusion of the ferroelectric thin film, whose permittivity can be tuned by an external electric field. The dependence of tunability on the thickness of the layers, as well as the operating temperature, was explored within the (K_u) band of the spectrum. The effect of spurious magnetic fields on the superconducting strip, and thereby on the propagation characteristics of the waveguide, was also investigated. The tunable propagation characteristics of microwave waveguides obtained suggest the potential for application in satellite communication, in radar systems, and in circuit quantum electrodynamics.

The glycol-thermal technique synthesized Zn_0.7Ni_0.3RE_0.1Fe_1.9O₄ (RE = 0, Gd, Sm, Dy) nanostructured ferrites with fine particles in the 8–13 nm range. X-ray diffraction (XRD) data confirmed a single-phase cubic spinel structure with no impurity peaks for the samples investigated. High-resolution transmission electron microscopy (HrTEM) showed nearly spherical particle images for the pure Zn_0.7Ni_0.3Fe₂O₄. HrTEM images for Zn_0.7Ni_0.3RE_0.1Fe_1.9O₄ (RE = Gd, Sm, or Dy) rare-earth-substituted fine particles revealed agglomerated particles with irregular shapes. Reduced particle sizes of rare-earth-substituted Zn-Ni compared to undoped compounds have been explained based on electron–electron repulsion of 4f electrons. Electron spin dynamics were investigated by electron spin resonance (ESR) measurements. A broad ESR signal with the highest intensity has been observed for the Sm-doped compound (Zn_0.7Ni_0.3Sm_0.1Fe_1.9O₄) with a particle size of about 8 nm. Broadening of the signal revealed stronger magnetic dipole interactions and narrower signals for Gd- and Dy-doped compounds indicate stronger superexchange interactions. The slightest ESR signal observed for the Gd-based (Zn_0.7Ni_0.3Gd_0.1Fe_1.9O₄) compound has been attributed to high spin–orbit coupling and the paramagnetic nature of Gd ions disrupting magnetic resonance. The evolution of the magnetic parameters, such as signal line width, intensities, and g-factors, as a function of the type of rare-earth ions, has been presented and correlated with the outer 4f electron number of rare-earth ions and particle size. Rare-earth-doped Zn_0.7Ni_0.3RE_0.1Fe_1.9O₄ (RE = Gd, Sm, Dy) nanostructured ferrites exhibit enhanced magnetic and structural properties, critical for advanced applications such as magnetic separation and biomedical imaging. This study demonstrates the influence of rare-earth doping on ESR parameters, particle size, and magnetization, providing insights into the role of 4f electron configurations.

MgB₂ is a promising candidate for commercial superconducting applications because, as grain boundaries in MgB₂ are not weak links, there are fewer limitations on the choice of processing technique compared to high-temperature superconducting (HTS) cuprates. MgB₂ bulks are usually manufactured by powder processing techniques followed by a sintering process. After sintering, the impurity phases such as MgO and MgB₄ along with porosity are formed which strongly affect the superconducting properties mainly the macroscopic path for supercurrent in MgB₂ bulks. Investigation of these microstructural features is essential to improve the superconducting properties of these bulks. In this work, high-resolution laboratory X-ray computed tomography (XCT) has been used to investigate the microstructure of MgB₂ bulks in three dimensions. The volume fraction of defects and impurity phases along with the size distribution of pores have been studied using this advanced technique. A comparison has been made between the data extracted from conventional characterization techniques such as XRD and SEM and those obtained from the advanced XCT analysis.

In the field of high-frequency magnetic impedance (MI) research, accurately describing the MI effect in multilayer nanostructured thin films remains a challenging task. A model to accurately describe high-frequency magnetoimpedance in the FeNi/Co/Cu/Co/FeNi five-layer nanostructured thin film is developed. The GMI response was obtained through the simultaneous solution of Maxwell’s equations and the Landau-Lifshitz equation. Through the induction of an effective bias field in the soft magnetic layer, the magnetostatic coupling between the soft and hard magnetic layers is taken into account. At frequencies up to GHz magnitude, symmetrically structured nanofilms are capable of obtaining a greater MI ratio through magnetic coupling. Furthermore, we demonstrate that modifying film properties and manipulating the bias field can lead to improved sensing performance. This study not only fills the gap in the theoretical model of five-layer nanostructured symmetrical films but also provides a theoretical foundation for the design and optimization of high-performance magnetic sensors operating at high frequencies. The findings presented in this paper hold potential to advance the development of high-frequency magnetic impedance sensors.

This study focuses on sintered NdFeB magnets and systematically examines the diffusion behavior and its impact on magnetic properties using three types of diffusion sources: DyF₃ powder, a mixed powder of DyF₃ and Pr₇₀Co₁₅Al₁₅ alloy, and Pr₆₀Dy₁₀Co₁₅Al₁₅ alloy powder. The findings demonstrate that the Pr₆₀Dy₁₀Co₁₅Al₁₅ alloy diffusion source produces the most favorable outcomes, with an enhancement in coercivity by 6.9 kOe. The composite diffusion source demonstrates a 5.83-kOe increase, while the fluoride diffusion source exhibits the least improvement, with a 4.21-kOe increase. The diffusion of DyF₃ is constrained by its high decomposition temperature and interference from F elements, which limit the depth of diffusion of Dy. The composite diffusion source, through the liquid-phase diffusion of Pr₇₀Co₁₅Al₁₅ alloy, has the effect of improving the wettability of grain boundaries and the channels of diffusion, which significantly increases the depth of diffusion of Dy elements. In the Pr₆₀Dy₁₀Co₁₅Al₁₅ alloy diffusion source, the synergistic diffusion of Dy, Pr, and Al elements enhances diffusion efficiency. Moreover, extending the diffusion time allows for further optimization of the grain boundary structure, thus facilitating deeper diffusion of Dy elements. This study thus demonstrates the superiority of the Pr₆₀Dy₁₀Co₁₅Al₁₅ alloy diffusion source, providing a crucial foundation for the efficient use of rare earth resources and the development of high-performance magnets.

As an environmentally friendly and efficient refrigeration method, magnetic refrigeration technology has always attracted the attention of researchers. In this paper, the research and development status of magnetic refrigeration technology and magnetic materials are discussed in depth, and the challenges faced by the technology are also evaluated. Firstly, the principle of magnetic refrigeration technology is introduced, and the research and development process and current development of room-temperature and low-temperature magnetic refrigeration systems are briefly described. Then, the simulation of magnetic refrigeration technology in the current era is discussed in detail, and the important role of calculation model in optimizing system design is emphasized. Secondly, this paper reviews the classification of magnetic refrigeration materials, including room-temperature magnetic refrigeration materials and low-temperature magnetic refrigeration materials, and further analyzes the current research process of magnetic refrigeration materials. Through the comparative analysis of different materials, find out the most suitable magnetocaloric materials. Finally, this paper not only summarizes the current situation of magnetic refrigeration technology, but also makes a prospect for the future development of magnetic refrigeration technology and magnetic materials. Through the in-depth elaboration and analysis of this review paper, it aims to provide theoretical and practical guidance for the further advancement of magnetic refrigeration and magnetic materials research.

The work is devoted to the study of the magnetic DC and AC susceptibilities, as well as to the analysis of spin dynamics (relaxation processes) of yttrium- and bismuth-doped rare earth holmium titanates. An influence of doping degree and the type of dopant on the magnetic properties of holmium titanates have been evaluated. The magnetization curves were measured. The measurement of frequency dependence of the AC susceptibility allowed us to analyze spin dynamics and estimate characteristic magnetic relaxation times in the studied systems.

Superconductors with the A15 structure are prototypical type II s-wave superconductors which have generated considerable interest in early superconducting material history. However, the topological properties of the electronic structure remain unnoticed. In this study, we used first-principles calculations based on density-functional theory to investigate the structure, electronic properties, surface states, and topological properties of A15-type Mo₃Si compounds. The thermodynamic properties show that Mo₃Si exhibits thermodynamic stability, and its band structure and density of states indicate that Mo₃Si is a metallic compound. Meanwhile, the next calculations show the existence of potential topological properties of Mo₃Si, with suspected Dirac cones and many multiple concatenation points with linear dispersions in the vicinity of the Fermi energy level. In addition, the study of edge states suggests that topological surface states are highly likely to exist in Mo₃Si, revealing its potential applications in electron transport and quantum information processing. Its unique structural properties suggest that Mo₃Si is highly likely to be a topological material with broad potential applications.

In this work, the change in the energy and structure of local many-particle states of HTSC cuprate La(_{2-x})Sr(_x)CuO(_4) under the uniaxial compression along the c-axis is studied. Local copper-oxygen states are obtained using exact diagonalization of the CuO(_6) octahedron as a part of the GTB method for the five-band p-d model. The dependence of interatomic distances on the c-axis compression is calculated according to Hooke’s law using elastic constants; the influence of interatomic distances on the on-site energies and hopping integrals is obtained using linear extrapolation of the results of ab initio calculations and the theory of MT-orbitals, respectively. The c-axis compression leads to a decrease in the energy of hole states with the nature of the (a_{1g}) symmetry orbitals. At a pressure value of (P_{c1}^{left( c right) } = 11.8) GPa, a spin crossover between the Zhang-Rice singlet and the triplet state (B_1) occurs. At higher pressures, a second spin crossover between two-hole states and a crossover of single-hole states with different orbital compositions were also detected. Taking into account the competition of various local states with changing the value of uniaxial compression, the effective five-band Hubbard model is formulated to describe the electronic structure of quasiparticle excitations.