Journal of Superconductivity and Novel Magnetism最新文献

Lead-free magnetoelectric (ME) ceramic particulate composites of the type (y)Cd_1-xNi_xFe₂O₄ + (1–y) BaZr_0.2Ti_0.8O₃ (with weight fractions y = 0.1, 0.2, 0.3 and x = 0.1, 0.2, 0.3)were synthesized using the conventional solid-state reaction technique. Powder X-ray diffraction (XRD) confirmed the coexistence of ferrite and ferroelectric phases in the composites sintered at 1100 °C. Scanning electron microscopy (SEM) revealed detailed information on surface morphology, grain size, and porosity, with average grain sizes ranging from 1.08 to 3.80 µm. Energy-dispersive X-ray spectroscopy (EDX) was employed for elemental analysis and detection of possible foreign phases. Dielectric studies were carried out by measuring the dielectric constant (ε′) and dielectric loss tangent as functions of frequency (40 Hz–1 MHz) and temperature (30–650 °C) at four fixed frequencies (1 kHz, 10 kHz, 100 kHz, and 1 MHz).The dielectric constant showed a sharp decrease at lower frequencies, stabilizing to a constant value at higher frequencies. Magnetic characterization at room temperature exhibited well-defined M–H hysteresis loops, confirming the presence of an ordered magnetic structure in the ferrite–ferroelectric composites. The magnetoelectric effect, measured as a function of magnetic field intensity, displayed a linear variation. The static ME voltage coefficient [(dE/dH)H] was composition-dependent, with the maximum magnetoelectric voltage coefficient (α) recorded as 15.103 mV/cm·Oe for the composite with y = 0.2 and x = 0.3. The nearly constant magnetoelectric conversion factor further indicated that magnetostriction reached saturation during magnetic poling, resulting in a stable induced electric field in the ferroelectric phase.

We theoretically study Josephson junctions that contain higher Josephson harmonics in the current-phase relationship using numerical simulations in the resistive-shunt junction model. We call these junctions non-ideal Josephson junctions. Our main focus is on the current–voltage characteristics of non-ideal junctions in the current-bias case. Deviations of the characteristics of these junctions from those of ideal (standard) junctions are studied numerically. It is established that the current–voltage characteristics remain unchanged with significant deviations of the current-phase relationship from a simple sinusoidal dependence. Also, the dependences of the height of the Shapiro current steps on the amplitude of the incident radiation are calculated. Some deviations of these dependences from the corresponding dependences for ideal Josephson junctions are found. In our work, we consider the features of the appearance of additional current steps on the current–voltage characteristics of non-ideal Josephson junctions, and also show the possibility of their absence in the case of the existence of additional Josephson harmonics. The results of our work prove that by analyzing the structure of the Shapiro steps of the current–voltage characteristics, it is possible to obtain information about the properties of Josephson junctions and the superconductors that form them.

This study investigates the thermophysical properties of gadolinium (Gd), terbium (Tb), and their binary compounds Gd_xTb_(1-x) (x = 0.25, 0.50, 0.75) using mean field theory. The study focuses on calculating magnetocaloric parameters, including magnetic entropy, its variation with magnetic field, specific heat, and the adiabatic temperature change, across magnetic field (B) intensities from 0 to 9 T. The findings indicate that the magnetic entropy has a considerable response to the applied magnetic field, demonstrating a 9.28% reduction in magnetic entropy for Gd at a temperature of 300 K when the field strength escalates from 1.5 to 9 T. Tb has a larger (Delta {S}_{text{m}}) than Gd under similar conditions. In Gd_xTb_(1-x) compounds, increasing Gd concentration results in a higher Curie temperature, approaching pure Gd, while the peak (Delta {T}_{text{ad}}) shows a little decline. The peak values of (Delta {T}_{text{ad}}) are 6 K, 5.86 K, and 5.76 K for x values of 0.25, 0.5, and 0.75 in Gd_xTb_(1-x), respectively, at B 1.5 T. Moreover, Tb demonstrates a significantly higher relative cooling power than Gd, being approximately 34.91% higher at a given B of 1.5 T, whereas Gd and Gd-rich compounds display higher refrigeration capacity in the 250–320 K range. These results provide theoretical insights into the magnetic field–dependent magnetocaloric behavior of Gd, Tb, and Gd_xTb_(1-x) compounds, while highlighting the compositional effects in Gd_xTb_(1-x) compounds.

Li₂VMnBr₆ double perovskite material was obtained as a ferromagnetic semiconductor. The semiconductor band gaps for the spin-up orientations are 0.3725 eV, 1.7943 eV, and 2.0627 eV for the GGA + PBE, GGA + 3 eV, and GGA + 4 eV approximations, respectively. For the spin-down orientations, these gaps are -2.4070 eV, 3.0968 eV, and 3.0875 eV. The 10.52 Å is the lattice constant at the equilibrium point. Li₂VMnBr₆ is mechanically stable. While it shows ductile character at 0 GPa pressure, it turns into a brittle structure after 10 GPa with increasing pressure. According to the Gibbs energy value, it is also structurally stable at low pressure. According to elastic and thermodynamic calculations, the Debye temperatures at the initial conditions were 212.264 K and 240.76 K. The Curie temperature and formation energy values were obtained as 303 K and -1.291 eV, respectively. The total magnetic moment of Li₂VMnBr₆ double perovskite is obtained as 8.00 µ_B. The most partial contributions come from Mn and V-atoms with the values ​​of 4.4699 µ_B and 2.6219 µ_B. The structural, electronic, and magnetic characteristics of Li₂VMnBr₆ double perovskite material and its elastic properties make it a highly efficient alternative material for semiconductor technologies.

In this work, we investigated the critical behavior and magnetocaloric effect of Pr_0.55Sr_0.45-xNa_xMnO₃ manganites (x = 0, 0.05 and 0.1) by using critical exponent analysis and Landau theory. The study revealed that the mean-field, 3D-Heisenberg and 3D-XY models are the best for describing the magnetic interactions for x = 0, 0.05 and 0.1 samples, respectively. With increasing sodium content, the magnetic interactions display a striking change from long-range to short-range interactions, which may be ascribed to an increase in Mn⁴⁺ ions concentration and magnetocrystalline anisotropy. Using Landau theory, we have confirmed that the magnetic transition around T_C is of second-order. An agreement was found between the magnetic entropy change values estimated by Landau theory and those obtained using Maxwell relation for a magnetic field equal to 2 T. This confirms the validity of Landau theory to estimate the magnetocaloric effect of Pr_0.55Sr_0.45-xNa_xMnO₃ samples. The small deviation obtained for our samples below T_C can be attributed to the existence of magnetic disorder in the ferromagnetic phase.

Magnetic hyperthermia therapy represents a cutting-edge oncological treatment that harnesses the localized heating of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF). In this study, monodisperse nickel ferrite (NiFe₂O₄) nanoparticles were synthesized via a controlled thermal decomposition strategy to achieve optimized magnetic characteristics suitable for biomedical hyperthermia. The synthesis conditions were systematically tuned using 7.5 mmol of oleylamine and oleic acid as surfactants, yielding highly uniform nanoparticles with enhanced superparamagnetic properties. Structural and morphological characterization using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) confirmed the formation of a pure spinel phase with narrow size distribution, while magnetic measurements via vibrating sample magnetometry (VSM) revealed a high saturation magnetization of 29.1 emu/g and low coercivity of 58.3 Oe. Notably, the obtained SLP value of 85.3 W/g under 400 Oe and 400 kHz confirms the heating capability of the nanoparticles for magnetic hyperthermia applications. These findings establish thermally tailored NiFe₂O₄ nanoparticles as promising candidates for advanced magnetically driven therapeutic platforms.

In this work, we investigated the XRD patterns, magnetic measurements, and critical phenomena of La_0.8 Na_0.2 Mn_1–x Ga_xO₃ (x = 0, 0.025). The samples crystallize in the rhombohedral structure with R-3C symmetry. Magnetic data show that the compounds undergo a ferromagnetic-paramagnetic phase transition around the Curie temperature (T_C). We observed that T_C decreases from 297 to 290 K with 0.025 of Ga doping. Additionally, the magnetic entropy change (ΔS_M) reaches its highest values around T_C during the order-disorder transition. At a Magnetic field of 5 T, −ΔS_M is 4.5 J·kg⁻¹·K⁻¹ for the parent compound and 4.3 J·kg⁻¹·K⁻¹ the doped sample. However, the relative cooling power (RCP) increases with the Ga doping, with RCP values of 279 J·kg⁻¹ and 299 J·kg⁻¹ for x = 0 and 0.025 respectively. We confirmed that both materials undergo a second-order magnetic phase transition based on the universal master curve and the Banerjee criteria. From the critical behavior analysis, we found that the samples conform well to the mean-field model with (β = 0.49 and 0.48, γ = 1 and 0.95; δ equal to 2.87 and 3.10 for x = 0 and 0.025, respectively).

Magnesium-doped nickel–cobalt ferrite in nanoscale form can be created using a sol–gel process. The crystallite diameters, varying from 42 to 73 nm, are confirmed by XRD examination. Ferrimagnetism, a form of magnetism in which the material’s magnetic moments align to produce a net magnetic field, is shown by synthesized ferrites. As the frequency rises, the ac resistivity changes in all the samples, showing a decreasing trend, which is typical of ferrites. These variations are explained by the electronic hopping between ferrous ↔ ferric ions and the concentration of ferrous ↔ ferricions on octahedral sites. An LCR-Q meter and a frequency function were used to examine the samples’ initial permeability. The actual part of early permeability was observed to rise. By taking into account both resistance (actual component) and reactance (imaginary part), a complex impedance analysis examines the resistance to alternating current (AC) flow in a circuit or material. The electrical characteristics and conduction processes of the material are revealed by this investigation, which is frequently carried out utilising sophisticated impedance studies.

Herein, manganese-doped magnesium zinc ferrite nanoparticles were synthesized using co-precipitation method. X-ray diffraction (XRD) analysis of the ferrite samples showed a pure spinel phase (Mg_0.5Mn_xZn_0.5-xFe₂O₄) with a cubic spinel structure where crystallite size was observed in the range of 13 to 18 nm, whereas the lattice parameter increased from 7.678 to 7.726 Å with an increase in Mn²⁺ ion concentration. The increase in crystallite size was coupled with a reduction in the lattice strain, which ranged from 0.020 to 0.007. FTIR studies showed that when Mn²⁺ ion doping increased, the band location in the high-frequency band region decreased from 565.182 to 418.779 cm⁻¹. Five Raman active vibrational modes at 180–700 cm⁻¹ were visible in the Raman spectra. With low coercivity, the nanoferrites displayed excellent magnetization values from 24.44 to 42.11 emu/g. A single semicircular arc in the Cole–Cole plot described grain dominance. According to the impedance spectrometry plot, composition x = 0.4 exhibited the highest ac conductivity, 0.000137 S/cm, at 10 MHz frequency, and the lowest tangent loss value, 0.553, at 1.12 MHz frequency for x = 0.0 composition. As the doping level increased, the ac conductivity increased as well. None of the samples exhibit Debye behavior, as indicated by the wide range of conductivity values. The substitution of manganese ions not only affected the structural characteristics of the nanoferrites but also significantly impacted their electrical conductivity from 0.34 × 10⁻⁴ to 1.3 × 10⁻⁴ S/cm. These changes made Mn-substituted Mg–Zn nanoferrites promising candidates for various applications in magnetic devices and energy storage systems.

The pursuit of viable superconducting and topological materials stands at the forefront of condensed matter physics, as these systems harbor a multitude of exotic quantum phenomena rooted in their distinctive electronic structures. In this study, we employ advanced first-principles density functional theory to systematically probe the topological and superconducting properties of hexagonal TaC and trigonal Ta₂C. Our electronic structure calculations reveal that hexagonal TaC is a Wely semimetal witch hosts Weyl nodes and a nodal ring without spin–orbit coupling (SOC). Moreover, relativistic trigonal Ta₂C demonstrates a robust nontrivial topological phase characterized by a nonzero Z₂(1; 000) invariant. Phonon dispersion analyses confirm the dynamical stability of both phases, with superconducting critical temperatures T_c of 17.33 K for hexagonal TaC and 1.37 K for trigonal Ta₂C. The enhanced superconductivity in hexagonal TaC stems from the strong Bardeen-Cooper-Schrieffer electron pairing mediated by Ta-d electrons and significant contributions from both Ta-acoustic and C-optic phonon modes. In contrast, the markedly lower T_c of trigonal Ta₂C, approximately an order of magnitude less than its hexagonal counterpart and slightly below the experimental measurement of 4.1 K, is attributable to weaker electron–phonon coupling and a diminished density of states at the Fermi level.