Journal of Superconductivity and Novel Magnetism最新文献

The current-voltage characteristics (CVC) of superconducting niobium nitride (NbN) films are obtained at temperatures below the superconducting transition temperature (T_c) at T = 15.4 K in a constant magnetic field. For magnetic fields of up to µ₀H = 0.5 T, regions of linear CVCs with differential resistance independent of the magnetic field are observed. The resistive state of the films in this case is not described by the usual magnetic flux flow. The presence of such CVC regions is explained by an additional constant force (independent of magnetic field) acting on the vortex lattice. The origin of this force may be associated with collective pinning of the lattice on atomic-scale inhomogeneities, which are always present in niobium nitride. In addition, pinning can be associated with grain boundaries and strong intervortex interactions. In this case, the motion of a weakly pinned part of the vortex lattice in an environment of strongly pinned vortices near T_c in fields up to 0.5 T is possible.

The structural, electronic, thermoelectric, magnetic, thermodynamic, elastic, and optical properties of the antiperovskite compound CaCNi(_3) are explored from first principles using DFT-based TB-mBJ and GGA(+U) methods. Structural optimisation validates system stability at a ground-state energy of (-10552.36) Ry and an equilibrium volume of around 378 a.u(^3). The electron localisation function (ELF) shows significant covalent and ionic bonding, whereas electronic structure simulations show a metallic nature dominated by Ni-3d orbitals. The BoltzTraP evaluation of thermoelectric performance indicates moderate energy conversion potential, with a maximum figure of merit of (ZT approx 0.26) at 1000K at (mu = +0.035) eV. Pugh’s ratio = 2.23 confirms mechanical stability and ductility, while decreasing Gibbs free energy and increasing entropy up to 1200 K indicate thermodynamic stability. GGA(+U) magnetic analysis shows a limited net magnetic moment in CaCNi(_3), which is confirmed by the spin-polarized density of states (DOS), which shows asymmetric spin channels and validates its ferromagnetic metallic nature. Optical examination confirms metallic behaviour with strong UV absorption ((varepsilon _2) peak (sim 8) eV), high reflectivity ((sim 0.83)), and a large static dielectric constant ((varepsilon _1(0) = 35.50)). CaCNi(_3) is a versatile material for high-temperature thermoelectrics, spintronics, and optoelectronics.

Lanthanum-modified strontium–nickel hexaferrite nanoparticles were produced using an auto-combustion sol–gel route to assess their potential as microwave absorbers. A set of compositions, Sr_0.50Ni_0.50La_xFe_12−xO₁₉ (x = 0.00, 0.25, 0.35, 0.50), was synthesized to study how gradually replacing Fe with La influences the structural, magnetic, dielectric, and electromagnetic attenuation behavior. The successful formation of the M-type hexaferrite phase is verified by XRD patterns, showing only slight lattice variations caused by Ni presence, and crystallite dimensions ranging from 29 to 48 nm. The FTIR spectra revealed characteristic metal–oxygen stretching vibrations corresponding to both tetrahedral and octahedral coordination sites, confirming the structural purity of the samples. Magnetic measurements obtained via VSM demonstrated that La substitution enhances the saturation magnetization, which increased from 50.66 to 59.29 emu/g. For x = 0.35, coercivity decreased significantly, dropping from 3956 Oe to 3110 Oe for x = 0.50 and further down to 2829 Oe, showing the evolution toward soft-magnetic behavior desirable for microwave-absorbing materials. The dielectric and magnetic responses, evaluated through the real and imaginary components of permittivity and permeability, showed that µ′ from 1.69 to 2.51 and ε′ increased from 4.23 to 8.64 at x = 0.35, revealing improved magnetic resonance effects and interfacial polarization. Among all prepared compositions, the x = 0.35 sample offered the most balanced electromagnetic properties, with ε′ = 11.84, ε″ = 5.16, µ′ = 2.73, and µ″ = 7.42 at 1 GHz, validating its superior microwave attenuation performance. Reflection loss measurements in the X-band (8–12 GHz) confirmed strong absorption for all samples, with the x = 0.35 composition showing the best result, a normalized impedance (Zin/Z0) close to 0.8, signalling excellent impedance matching at 9.45 GHz with minimum RL of − 39.26 dB. These findings establish La-doped Sr–Ni hexaferrite nanoparticles as lightweight, adjustable, and highly effective candidates for stealth and electromagnetic shielding applications.

The effects of hydrostatic pressure on the antiferromagnetic orthorhombic phase in iron-based ladder compounds AFe₂Q₃ (A = Ca, Ba, Sr; Q = S, Se) have been investigated using the density-functional theory beyond the generalized gradient approximation, where the strong induced correlations from iron ion d-orbitals were treated by the Hubbard potential. This study aims to predict new Mott insulators by examining several properties under pressure, such as crystal structure, antiferromagnetic phase, insulator-metal transition, local magnetic moment, strong electronic correlation and density of states behavior. By carefully analyzing these properties and comparing them with existing experimental and theoretical data, we can assess the potential classification of these systems as Mott materials. Indeed, GGA + U calculations confirm the presence of an insulator-metal transition under pressure in all studied 123-materials. Local magnetic moments decrease with pressure, indicating the weakening of correlation effects in metallic systems. A zero local magnetic moment indicates the presence of a non-magnetic or probably superconducting phase. Thus, the physical and electronic similarities between Mott insulators and our four hypothetical materials suggest they are potential candidates exhibiting Mott-like character.

Microspheres of CoFe_xNi_2−xS₄ (x ≤ 0.06) nanothiospinels (NTSs) were successfully synthesized hydrothermally. The influence of Fe³⁺ ion substitution on the morphology, structure, and magnetic performance of the products is carefully investigated. Magnetic properties of CoFe_xNi_2−xS₄ (x ≤ 0.06) NTSs are analyzed at 300 K (RT) and 10 K between ± 50 kOe. At both temperatures, ferromagnetic nature (and hysteresis loops) is not detected for samples with x < 0.03. For the host sample (x = 0.00), while a diamagnetic behavior was observed at 300 K, paramagnetic behavior was exhibited at 10 K. Kinks, showing up in the hysteresis loops at 10 K, disappear at 300 K. The coercivity values of Fe-doped NTSs (0.03 ≤ x ≤ 0.06) at both at RT and 10 K demonstrate their magnetically hard nature. These results highlight that the Ni dopants can be harnessed to achieve desired magnetic properties of CoFe_xNi_2−xS₄ NTSs. The obtained findings show the potential for tuning the magnetic properties of CoFe_xNi_2−xS₄ nanothiospinels, making them promising candidates for use in spintronics, magnetic data storage, and sensors.

Ni_0.5Zn_0.5RE_0.05Fe_1.95O₄ (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Y) powders were synthesized using the sol-gel self-combustion method, and the effects of RE³⁺ doping and sintering temperatures on their structure, magnetic properties and electromagnetic wave absorption performance were studied. X-ray diffraction (XRD) studies indicate lattice distortion in Ni-Zn ferrites results in an increase in lattice constants and a decrease in grain size, and the secondary phase REFeO₃ (CeO₂) is observed. This indicates that the solid solution limit of rare earth ions in nickel zinc ferrite is relatively small, and the formation of the second phase may lead to iron deficiency in the primary phase. Scanning electron microscopy (SEM) results demonstrate that RE³⁺ion doping makes the grain distribution more uniform. Vibrating sample magnetometer (VSM) analysis reveals that doping with RE³⁺ ions decreases the saturation magnetization of Ni-Zn ferrites and the change in coercivity is related to the sintering temperature. Under sintering conditions of 900 °C, RE³⁺ion doping increases the coercivity of Ni-Zn ferrite, while under sintering conditions of 1250 °C, RE³⁺ion doping decreases the coercivity. Vector network analyzer (VNA) test results indicate that doping with RE³⁺ is difficult to increase the dielectric loss of NZFO in the gigahertz frequency band, but it can enhance the impedance matching effect. At lower sintering temperatures, rare earth doping is beneficial for nickel zinc ferrite to improve reflection loss and expand absorption bandwidth. while at higher sintering temperatures, due to significant grain growth, the influence of the second phase generated by rare earth doping on the main phase is significantly reduced. The minimum reflection loss of Ni_0.5Zn_0.5Dy_0.05Fe_1.95O₄ sintered at 900/3 is -22.38 dB, with a corresponding effective absorption bandwidth (EAB) of 3.39 GHz, and the EAB of Ni_0.5Zn_0.5Pr_0.05Fe_1.95O₄ in the C and Ku band is 4.23 GHz.

This study presents the first systematic investigation of Fe and Co additions on the structure-property relations in (Ni₈₀Si₂₀)₉₅M₅ (M = Fe, Co) ternary alloys. The alloys were fabricated using vacuum arc melting and characterized by XRD, SEM/EDX, DSC, DTA, VSM and Vickers microhardness measurements. XRD analysis revealed larger crystallite sizes for (Ni₈₀Si₂₀)₉₅Fe₅ (29.40 nm) compared to (Ni₈₀Si₂₀)₉₅Co₅ (26.11 nm), and the phases observed in both alloys are consistent with the Ni–Si binary phase diagram. SEM observations corroborated these findings, displaying regular, parallel lamellar structures for (Ni₈₀Si₂₀)₉₅Fe₅ and irregular dendritic structures for (Ni₈₀Si₂₀)₉₅Co₅. Thermal analysis demonstrated high stability up to ~ 1100 ℃ for both alloys, with distinct melting behaviors at higher temperatures. VSM measurements revealed soft magnetic properties in both alloys, with the Fe-containing alloy exhibiting higher saturation magnetization (21.97 emu/g) but lower coercivity (2.31 Oe) compared to the Co-containing alloy (8.47 emu/g and 13.24 Oe, respectively). Additionally, Fe substitution enhanced mechanical properties, achieving significantly higher hardness (885.0 ± 61.0 HV) compared to Co substitution (780.6 ± 51.7 HV). These findings establish novel property–composition correlations in (Ni₈₀Si₂₀)₉₅M₅ alloys, offering valuable insights for designing next-generation soft magnetic materials for advanced applications.

Nanocrystalline boron carbide (B₄C) was probed by room-temperature X-band EPR before and after controlled neutron exposure to reveal irradiation-driven changes in defect populations and local symmetry. Pristine powders show a multi-component spectrum with an orthorhombic g-tensor. With increasing neutron fluence (10¹⁵–10¹⁷ n·cm⁻²), the response converges to a stronger, more symmetric resonance near g ≈ 2.00 that exhibits clear peak-to-peak broadening (ΔB_pp). These trends are consistent with boron transmutation—dominantly ¹⁰B(n,α)⁷Li and, secondarily, ¹¹B(n,γ)→¹²B→¹²C—creating vacancies and defect complexes, increasing spin concentration, enhancing dipolar interactions, and partially averaging g-anisotropy. Carbon channels are negligible at thermal energies. The results provide a concise, mechanism-anchored picture of defect evolution in irradiated B₄C and establish g, ΔB_pp, and integrated intensity as practical spectral markers for monitoring neutron-induced changes in boron-rich ceramics.

With the aim of obtaining a material with interesting magnetocaloric and optical properties. We prepared by sol–gel method The La_0.57Nd_0.1Sr_0.18Ag_0.15CoO₃ (LNSACO) compound. This prepared material has a rhombohedral crystal structure with R-3c space group. According to the conventional ZFC and FC processes, magnetization curves as a function of temperature clearly exhibit a paramagnetic/ferromagnetic transition at Tc = 225 K. The observed irreversibility between FC and ZFC modes at the irreversible temperature Ti = 210 K is assigned to the existence of magnetic anisotropy. By adjusting the hysteresis loop using an empirical formula, different magnetic parameters such as the coercive field ((:{H}_{C})), the remanent magnetization (:{(M}_{r}),:)the saturation magnetization ((:{M}_{s}^{FM})) and the squareness ratio ((:{S}_{qr})) are selected. The existence of double coercive field indicates the presence of the exchange bias effect, proving the material’s suitability for a variety of technological applications including spintronic and magnetic head devices. The optoelectronic uses of cobaltite material have been highlighted by a more in-depth study of the refractive index, penetration depth, extinction coefficients. The bandgap values ​​obtained make them good promising candidates for the absorption of visible light.