Journal of Superconductivity and Novel Magnetism最新文献

This study explores the structural, mechanical, vibrational, and superconducting properties of magnesium hexahydride (MgH₆) under high pressure using first-principles density functional theory (DFT) with the generalized gradient approximation (GGA-PBE). Phonon dispersion calculations, performed via density functional perturbation theory (DFPT), reveal that MgH₆ achieves dynamic stability above 295 GPa, as evidenced by the absence of imaginary frequencies in the vibrational spectrum. While imaginary modes persist at lower pressures (150–290 GPa), their localized nature ensures minimal impact on the overall electron–phonon coupling strength. The calculated elastic constants satisfy the Born-Huang criteria, confirming mechanical stability across the 150–400 GPa range. By solving the Migdal-Eliashberg equations with a Coulomb pseudopotential (μ^* = 0.136), we predict a maximum superconducting critical temperature (({T}_{C})) of 238 K at 290 GPa. This peak ({T}_{C}) correlates with enhanced coupling from phonon softening near the stability threshold, underscoring the interplay between dynamic stability and superconductivity. Our results highlight MgH₆ as a promising high-temperature superconductor and provide insights into the stabilization mechanisms of hydrogen-rich compounds under extreme conditions.

Using Monte Carlo simulation (MCS), we study thermal and hysteresis behaviors of a mixed spin-1/2 and spin-3/2 ferromagnetic Ising model in the presence of crystal and external magnetic fields for a quasi-one dimensional system characterized by a lattice of length (textrm{L}) and width (textrm{L}') with (textrm{L}'ll textrm{L}). We show that the effect of the external field on the form of the susceptibility curve is related to the change of (textrm{L}). Our results reveal that this system exhibits a first- to second-order phase transition at reduced temperature (t=0.5). Critical exponents are also calculated and compared with those obtained in previous studies. The ground-state phase diagrams of the system are also reported at temperature (textrm{T}simeq 0).

We utilized 3D-MLSI (three-dimensional magnetic low-temperature superconducting interference) simulations to investigate the inductance and effective areas of slit-shape SQUIDs, directly coupled magnetometers, as well as one- and two-level coupled magnetometers. For slit-shape SQUIDs, the impact of five parameters, slit length, slit width, linewidth, film thickness, and London penetration depth, on the inductance was systematically evaluated. In the case of directly coupled magnetometers, with the outer side length of the pickup loop fixed at 10 mm, we explored the effect of varying the inner side length on the effective area. For both one- and two-level coupled magnetometers, flux transformers with square and circular input coils were designed, corresponding to square and circular apertures in the SQUID chip. The influence of the inner side length or inner diameter of the SQUID chip and the input coil on the inductance, mutual inductance, coupling coefficient, and effective area was analyzed. The results indicate that under the optimal parameter configuration, the directly coupled magnetometers achieved a maximum effective area of 0.35 mm(^2), one-level coupled magnetometers reached 4.5 mm(^{2}), and the two-level coupled magnetometers achieved 0.88 mm(^{2}). These findings provide valuable information on the design and optimization of magnetometers, with the goal of enhancing their effective areas and sensitivity to magnetic fields.

In this study we present the effect of the irradiation of sintered MgB₂ with protons of intermediate energies, from 8.6 to 15.07 MeV, at a constant fluence of 2.86 × 10¹⁶ p/cm². We found clear evidence that the disorder generated by irradiation leads to a weak suppression of the critical temperature T_c and an increase of the critical current density J_c with increasing proton energy, as expected. However, it was found that thermomagnetic instabilities and vortex creep phenomena strongly depend on the ratio between proton range and the sample thickness. The number of the macroscopic flux jumps (MFJ) is highest and manifest up to 28 K in the sample with the proton range shorter than sample thickness (P₁) and decrease as the proton energy increases. Similarly, the relaxation rate of the irreversible magnetization is the lowest in the sample P₁ and increases with proton energy. We tentatively attribute this effect to the protons that stop within MgB₂ and interact with the local structure/atomic composition.

Proximity-induced superconductivity with a clean interface has attracted much attention in recent years. We discuss how the commonly employed electron tunneling approximation can be hybridized with first-principles calculation to achieve a semi-quantitative characterization starting from the microscopic atomic structure. By using the graphene-Zn heterostructure as an example, we compare this approximated treatment to the full ab initio anisotropic Eliashberg formalism. Based on the calculation results, we show that interfacial effects beyond the electron tunneling approximation are noticeable even in a rather weakly coupled heterojunction.

Physical properties of stable polytypic Laves phase binary intermetallics PrB₂ (B = Cr, Mn and Fe) are investigated through DFT. The determined stable polytypic phases structural parameters reveal that PrCr₂ and PrMn₂ are stable in hexagonal and and PrFe₂ stable in cubic phase respectively and are consistent with experiments. The electron charge density plots show the hybrid metallic-covalent bond between Pr and B in these intermetallics. The ground state magnetic phase optimizations and magnetic susceptibilities suggest that all the understudy compounds are stable ferromagnetic phases. The electronic and electrical properties of these intermetallics confirm their metallic nature. The analysis of electrical resistivities reveal that PrCr₂ is a good conductor among the series. In addition, the computed elastic parameters demonstrate the mechanical stability of each polytypic phase; furthermore, these intermetallics are elastically anisotropic and incompressible.

Graphical Abstract

This study investigates the magnetic and spintronic properties of armchair (ANRs) and zigzag (ZNRs) nanoribbons of group-IV transition metal nitrides (MN, where M = Ti, Zr, Hf) through density functional theory (DFT) calculations. While bulk MN structures exhibit metallic character and lack magnetic properties, converting them into nanoribbon configurations induces significant bandgap openings and distinct magnetic behavior. Both ANRs and ZNRs demonstrate n-type semiconducting characteristics with indirect bandgaps, where ANRs display enhanced magnetic moments compared to ZNRs. Magnetic analysis indicates ferrimagnetic behavior, attributable to polarization between metal d-orbitals and nitrogen p-orbitals, resulting in a net magnetic moment without external dopants. Detailed Mulliken charge analysis reveals that nitrogen atoms consistently act as electron acceptors, establishing polar bonds that influence the electronic and spintronic properties of these nanostructures. This unique combination of bandgap tuning, magnetic moment, and polarization direction provides promising prospects for nanoscale applications in spintronics and memory devices.

In this study, the structural, magnetic, and magnetocaloric properties of Pr_0.9Sr_0.1Mn_0.9Ti_0.1O₃ were investigated. The sample was synthesized by the solid-state method. X-ray powder diffraction and magnetic measurements were used to investigate structure and magnetism, respectively. Rietveld analysis showed that the sample crystallized in the orthorhombic system with space group Pnma. Magnetic measurements were used to determine the Curie temperature and the spontaneous magnetization based on the magnetization as a function of temperature M(T) and applied magnetic field M(H). The analysis of the magnetic measurements shows the presence of a transition from a ferromagnetic state at low temperature (FM) to a paramagnetic state at high temperature (PM) for a Curie temperature T_C. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transitions in the sample. Magnetic entropy change (left|Delta {S}_{text{M}}right|) was calculated using the Maxwell relation method. The maximum values of entropy |(Delta {S}_{text{M}}^{text{max}}|) are 0.6055 to 2.6004 J/kg K with an applied magnetic field of 1 to 5 T. At these values of the magnetic field, the relative cooling power (RCP) values are 31.3 to 211.21 J/kg. At high temperatures, a large change in magnetic entropy was observed in the sample. Our results on magnetocaloric properties suggest that the Pr_0.9Sr_0.1Mn_0.9Ti_0.1O₃ compound can be used in magnetic refrigeration applications.

It is assumed that each Bethe lattice (BL) site is inhabited by a diatomic molecule composed of either two spin-1/2 or two spin-3/2 atoms. Then, each diatomic molecule is assumed to interact with others through its atoms in terms of a variety of bilinear interaction parameters, such as the interaction of atoms within each molecule and between molecules. The thermal variations of magnetizations in the diatomic molecule are investigated by including a crystal field for the spin-3/2 atoms and calculating their magnetic phase diagrams on the BL with the number of nearest-neighbor sites of (q=3) by using the exact recursion relations (ERR). The effects of the external magnetic field are also considered while examining the thermal variations in magnetizations. For various ferromagnetic (FM) and antiferromagnetic (AFM) interaction configurations, the model always displays second-order phase transitions when the external magnetic field is set to zero. The first-order phase transitions are observed for nonzero external magnetic fields for appropriate values of our parameters. The obtained results are compared to those of a BL, in which each site is connected to a single atom, and the other possible studies.

REBCO high-temperature superconducting tapes are widely used in high-field applications due to their advantages of large critical current density, high upper critical magnetic field, and high critical temperature. However, due to their layered structure, REBCO tapes are susceptible to various mechanical loads, including but not limited to torsional loads, in practical applications such as preparing cables or magnets. To this end, we developed a critical performance measurement device for REBCO tapes under torsional load. The critical current (I_C) degradation characteristics of REBCO tapes fabricated by Shanghai Superconductor Technology Co., Ltd (SSTC) with different structures under torsional load were studied. Several samples were measured to analyze the influence of the substrate thickness, copper layer thickness, and copper lamination thickness of REBCO tapes on the I_C degradation behavior. The results indicate that copper and copper lamination can provide significant protection for REBCO tapes under torsional loads.