Journal of Superconductivity and Novel Magnetism最新文献

Structural, magnetic, and electrical transport properties of discontinuous metal–insulator multilayers [Fe/SiO₂]₁₀/Sub with d_Fe = 2–7 nm and d_SiO2 = 3 nm under heat treatment up to 400 °C have been studied with the purpose of determining the possibilities of their practical application as a material for thermally stable magnetic devices or high-ohmic resistance for various electronic applications. The samples have granular structures with randomly distributed Fe nanoparticles, as shown by electron microscopy. The low (almost zero) and stable coercivity values under heat treatment indicate that the investigated systems could be used as a magnetic material for thermally stable magnetic devices. According to the results of the study of the temperature dependence of the magnetisation, there are no Fe atoms in the insulator matrix and very small particles of ferromagnetic material. It was demonstrated that the value of the blocking temperatures depends on the effective thickness of ferromagnetic layers. Even an insignificant increase of d_Fe from 5 to 7 nm leads to a significant growth of the blocking temperatures from 55 to 180 K. The structural changes can explain the blocking temperatures’ dependence on the Fe layer’s effective thickness and the annealing temperature.Experimental results demonstrate that the system [Fe(6)/SiO₂(3)]₁₀/Sub, annealed at a temperature of 300 °C, is characterised by the low temperature coefficients of resistance of − 35 ppm/°C and relatively high resistivity of 6⋅10⁻⁵ Ohm⋅m. The system [Fe(7)/SiO₂(3)]₁₀/Sub shows thermal stability after annealing up to 400 °C. Namely, in comparison with the as-deposited state, the temperature coefficients of resistance stay practically unchanged (250 ppm/°C), with an insignificant growth in resistivity value.

This research investigated the evolution of structure and vacancy defects caused by Nb ion substitution at the Mn site on the physical properties of gadolinium manganite (GdMnO₃) materials synthesized via the solid-phase reaction method. XRD analysis confirmed the single-phase structure of the synthesized GdMn_1-xNb_xO₃ ceramics and revealed lattice distortion resulting from the replacement of Mn³⁺ with Nb⁵⁺ ions. SEM results demonstrated a correlation between the grain size of the synthesized GdMn_1-xNb_xO₃ ceramics and the vacancy concentration. XPS analysis indicated that Nb⁵⁺ substitution modified the oxidation state of Mn and influenced the concentration of oxygen vacancies; notably, the dominant charge compensation mechanism varied with different Nb substitution levels. Positron annihilation experimental results indicated that Nb⁵⁺ substitution could affect the open volume and concentration of vacancies in the Gd_1-xNb_xMnO₃ system. Temperature and magnetic field dependent magnetization measurements showed that Nb⁵⁺ ion substitution enhanced the magnetization. The obtained results indicated that the properties of GdMnO₃ system could be optimized by introducing vacancies and converting the Mn³⁺ to Mn²⁺.

Addition of 0.5% Cr to the Fe₆₅Co₃₅ alloy resulted in an increase of hardness (215 HV to 296 HV), stiffness, and total magnetostriction from 23 × 10⁻⁶ to 65 × 10⁻⁶. This alloy exhibited also the highest relative magnetic permeability and lowest coercive field among all the alloys studied, reaching μ_r = 1020 in an applied field of only 360 A m⁻¹ and H_c = 650 A m⁻¹ (8.2 Oe). Consistent results among hardness, stiffness, EBSD, and magnetization as a function of temperature reasonably indicate that BCC ordering is present in the Fe₆₅Co₃₅ alloy and in the Cr added alloy; however, Cr + Ti added alloy would be single phased, either fully disordered or fully ordered. Magnetization thermal hysteresis (ΔM) occurs because of strong internal stress development due to Fe₆₅Co₃₅ and Cr-added alloy sample rapid cooling, ΔM being wider for Cr-added alloy. Results of hardness, stiffness, EBSD, and ΔM permitted the conclusion that in Cr-added alloy, internal stresses are stronger than in Fe₆₅Co₃₅ alloy.

This study systematically optimizes the epitaxial growth of CeO₂ buffer layers on IBAD-MgO substrates via multi-channel multi-beam pulsed laser deposition (MC-MB-PLD) to enhance the performance of YBa₂Cu₃O_7-δ (YBCO) coated conductors. Through parametric control of oxygen pressure (1–15 mTorr), target-substrate distance (30–60 mm), laser energy density (0.54–3.02 J/cm²), laser energy (250–325 mJ), and substrate temperature (750–900 °C), we determined that: A target-substrate distance of 45 mm (within the stable plasma zone) results in atomically smooth CeO₂ films with (002) orientation (RMS roughness: 0.8 nm). An optimal oxygen pressure of 10 mTorr combined with a laser energy of 300 mJ effectively eliminates a-axis grains and suppresses particulate defects. Substrate temperatures ≥ 850 °C achieve pure (002) orientation with in-plane and out-of-plane textures of 4.3° and 2.1°, respectively. YBCO films deposited on optimized CeO₂ buffers exhibit critical currents up to 91 A (J_c = 4.0 MA/cm² at 77 K, 0 T). Also, this paper prepared an 830-m long Y_1-xGd_xBa₂Cu₃O_7-δ (YGBCO) tape achieves uniform critical currents of 500 A (J_c = 3.85 MA/cm²) with ΔI_c < 5%, demonstrating the feasibility of MC-MB-PLD for industrial-scale 2G-HTS production.

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