Journal of Superconductivity and Novel Magnetism最新文献

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.

In this study, we conducted a comprehensive investigation of the structural, elastic, thermodynamic, electronic behavior, magnetism, thermoelectric performance, and superconducting properties of HoAs and HoSb alloys using density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) method in the WIEN2k code. Due to the presence of heavy elements, spin–orbit coupling (SOC) effects were explicitly incorporated into all computations. Our findings reveal that the antiferromagnetic type-III phase is the most stable magnetic configuration for both compounds. Through full analysis, we demonstrate that HoAs and HoSb exhibit promising properties suitable for various technological applications. Moreover, we highlight a significant influence of hydrostatic pressure on the topological properties, which induces a phase transition from trivial to nontrivial semimetal for both compounds. Pressure also enhances their superconducting properties, increasing the critical temperature T_c from 1.5 K to 2.62 K and from 1.23 K to 2.53 K for HoAs and HoSb, respectively.

Gas-tight containers with the crystal hydrate K₂CO₃·1.5H₂O and powdered YBa₂Cu₃O_6+δ (YBCO) exhibited a puzzling sharp loss of part of their weight during and after 0.5 h of exposure to a magnetic field with a frequency of 50 MHz. A dependence of the weight loss magnitude on the oxygen content in YBCO shows a significant dip in the region where oxygen orderings exist in the basal plane. The connection of the inexplicable weight changes with the structural features of YBCO is discussed.

A comprehensive first-principles study of the structural, electronic, elastic, and thermodynamic properties of CdV₂O₄, MgV₂O₄, and ZnV₂O₄ spinel compounds has been performed using density functional theory (DFT) within the local density approximation (LDA). The calculations were carried out using the CASTEP Package. Our results show that all three compounds exhibit semiconducting behavior with complex electronic structures dominated by V 3d and O 2p states. The calculated lattice parameters demonstrate excellent agreement with experimental data, with deviations less than 3%. The bulk moduli follow the order ZnV₂O₄ (208.2 GPa) > MgV₂O₄ (174.2 GPa) > CdV₂O₄ (165.2 GPa), correlating inversely with the ionic radii of the A-site cations. Elastic properties analysis confirms mechanical stability for all compounds, with MgV₂O₄ showing the highest elastic anisotropy (A = 1.383). The pressure–volume relationships follow the Birch-Murnaghan equation of state, enabling accurate prediction of high-pressure behavior. Thermodynamic calculations reveal that heat capacities approach the classical Dulong-Petit limit at elevated temperatures, with Debye temperatures of 576.61 K, 615.04 K, and 716.91 K for CdV₂O₄, MgV₂O₄, and ZnV₂O₄, respectively. These findings provide fundamental insights into the structure–property relationships of vanadium-based spinel compounds for potential applications in electronic devices, high-pressure technologies, and thermal management systems.

This study investigates the magnetic characteristics of a mixed-spin model (σ = 2 and S = 3/2) residing on a specific geometric framework known as the square-hexagon-octagon. Leveraging Monte Carlo simulations, we scrutinize RKKY-type interactions, meticulously examining the ramifications of lattice vibrations, as well as exchanging coupling parameters contingent on time and temperature. Our investigations unearth magnetic phase transitions, encompassing magnetic spin reorientation and transitions from ferrimagnetic to paramagnetic states. Moreover, we dissect hysteresis loops, delineating their susceptibilities to non-magnetic layer thickness, exchange interactions, temperatures, and crystalline fields. These findings markedly enhance our comprehension of magnetic phenomena within intricate structural configurations.