Journal of Superconductivity and Novel Magnetism最新文献

This study investigates the properties of AlB(_{varvec{2}})-type YB(_{varvec{2}}) and YGa(_{varvec{2}}) compounds using density-functional theory, focusing on elastic constants, electronic structure, mechanical behavior, and electron–phonon (e-ph) coupling. The results, aligned with theoretical predictions, are compared with MgB(_{varvec{2}}) to assess their superconducting potential. YGa(_{varvec{2}}) has larger structural dimensions but lower phonon frequencies due to gallium’s higher atomic mass. YB(_{varvec{2}}), on the other hand, shows a higher critical temperature (5.59 K), attributed to its stronger e-ph coupling and higher density of states at the Fermi level. Shorter B-B bonds in YB(_{varvec{2}}) enhance its band structure and raise the Fermi energy. Both compounds are mechanically stable, with YB(_{varvec{2}}) exhibiting higher shear resistance and stronger covalent bonding. Additionally, YB(_{varvec{2}}) has a higher Debye temperature (779.75 K) and sound velocities, indicating superior mechanical properties. These findings underscore YB(_{varvec{2}})’s promise as a superconductor with favorable e-ph interactions compared to YGa(_{varvec{2}}).

The Hall effect of several single crystal and thin-film samples of YBa(_{2})Cu(_{3})O(_{6+x}) with different carrier concentration was measured in the temperature interval from (T_{c}) to (T = 300 K). In this region, the Hall coefficient decreases exponentially with temperature according to a cut-off law where the characteristic parameter closely reproduces the pseudogap line when plotted as a function of the carrier concentration p. The strongly temperature-dependent Hall coefficient is interpreted in terms of the superposition of ordinary and anomalous Hall terms. The anomalous contribution is related to a Griffiths-type antiferromagnetic configuration that forms at the pseudogap line. The coefficients of the ordinary and anomalous terms show a complex dependence on the carrier concentration, suggesting the occurrence of a Fermi surface reconstruction at (papprox 0.14), where electron-type pockets are supposed to stabilize.

This study uses a computational method called Density Functional Theory (DFT) to examine the structure, electronic, optical, elastic, and magnetic properties of Sr₂GdMO₆ (M = Bi or Sb). The calculations revealed that both materials have a cubic crystal structure with slightly different lattice constants. Volume optimization of Sr₂GdBiO₆ and Sr₂GdSbO₆ in PM, FM, and AFM states reveals that Sr₂GdBiO₆ stabilizes in a non-magnetic PM phase, while Sr₂GdSbO₆ favors a magnetic ground state. The magnetic behavior is influenced by the B-site cation, with Bi suppressing and Sb promoting magnetic ordering. Their electronic structures reveal that Sr₂GdBiO₆, have band gap 2.06 eV for spin-up and 2.18 eV for spin-down. Similarly, Sr₂GdSbO₆, have band gap 3.26 eV for spin-up and 3.40 eV for spin-down. Optical investigations have shown strong absorption in the ultraviolet region, with peaks at 3.75 eV for Sr₂GdBiO₆ and 4.15 eV for Sr₂GdSbO₆. The materials Sr₂GdBiO₆ and Sr₂GdSbO₆ have stable mechanical properties, with bulk moduli of 112.18 GPA and 143.235 GPA, respectively. They possess a significant magnetic moment of 7 Bohr magnetons per gadolinium atom, primarily due to the contribution of its 4f electrons, indicating their strong magnetic nature. To accurately account for the interactions between electrons in these materials, a specific parameter called the Hubbard parameter (U) was adjusted to 6 electron volts (eV) for the Gd-4f orbitals. These findings demonstrate their potential applications in spintronics, ultraviolet optoelectronics, and mechanical devices.

In this work, we studied the role of Ba and Sr substitutions on the structural, morphological, magnetic, and magnetocaloric properties of the La( _{0.7} )Ca( _{0.3} )MnO( _3 ) manganite. The La( _{0.7} )Ca( _{0.2} )Ba( _{0.1} )MnO( _{3} ) and La( _{0.7} )Ca( _{0.2} )Sr( _{0.1} )MnO( _{3} ) manganites were synthetized using the combustion method. FT-IR, X-ray diffraction, and magnetization measurements were performed to investigate the crystallographic structure and the magnetocaloric properties. The samples exhibit a ferromagnetic behavior, and the ferromagnetic-paramagnetic transition occurs around the room temperature. The critical temperatures are 298.5 K and 308.7 K for the LCBM and LCSM samples, respectively. The maxima values of magnetic entropy at a field of 3T are 1.64 J/Kg K and 2.08 J/Kg K for the LCBM and LCSM samples. The LCSM manganite shows a better magnetocaloric performance, which could be related to an enhancement of the double exchange interaction due to the shorter average bond length between Mn and O ions for this sample. These results are in agreement with those reported in the literature, highlighting that the solution combustion synthesis route presents potential advantages, such as a faster and simpler route for obtaining manganites.

This study employs first-principles calculations based on density functional theory (DFT) with the GGA + U and TB-mBJ approximations to examine the structural, electronic, magnetic, and thermoelectric properties of MgCNi₃. The results reveal that MgCNi₃ is a weak ferromagnetic and metallic material, characterized by strong covalent bonding and a net magnetic moment of 0.15 μB per formula unit. Spin-polarized calculations further indicate that the material exhibits a non-zero magnetization, with the spin-up and spin-down electron densities showing distinct distributions. The thermoelectric evaluation demonstrates remarkable energy conversion efficiency, with a significant Seebeck coefficient and high figure of merit (ZT) across temperatures ranging from 300 to 900 K. The ZT plot suggests that P-type doping may offer the best performance. These findings provide critical insights into the material’s potential for applications in thermoelectrics, superconductors, and spintronics, emphasizing its suitability for integration into advanced functional devices.

When an ultracold fermionic superfluid gas becomes polarized, the system can undergo normal-superfluid phase separation. For a mass-balance polarized Fermi gas, the phase separation occurs under the Clogston–Chandrasekhar condition. Considering the separation, the relevant parameters of the system are calculated numerically. Using Bogoliubov coefficients and the density of states in the Fermi golden rule, we then investigate and discuss the effects of imbalance chemical potential and interaction strength on wave-induced power due to the time-dependent external wave at low temperatures on the BCS side of the BCS-BEC crossover.

The magnetization vs applied magnetic field curves of Fe( _{3} )O( _{4 } ) measured from vibrating sample magnetometer and the particle size distribution determined from transmission electron micrographs are compared to investigate the influence of magnetic anisotropy and particle size distribution on the magnetization analysis. The sample of Fe( _{3} )O( _{4 } ) nanoparticles is prepared by a chemical method. The structural characterization of the sample reveals that it is a nanocrystalline single phase magnetite system. The transmission electron microscope studies show that the sample has narrow particle size distribution with mean particle size of 12 nm. The magnetic characterization of the sample is measured as a function of temperature and applied magnetic field. The field cooled and zero field cooled curves of Fe( _{3} )O( _{4 } ) nanoparticles are measured in the presence of 250 G applied magnetic field. The bifurcation temperature of the curves is found to be 182 K. The blocking temperature of the system is observed at 154 K from zero field cooled curve. The magnetization curves as a function of applied magnetic field at temperatures of 200, 250, and 300 K are measured (up to ( pm 10 ) kG). The analysis of magnetization curves is done by fitting these in a mathematical magnetic expression, which takes into account the combined effect of particle size distribution and magnetic anisotropy. The magnetic properties of this system are found to be affected by the presence of the magnetic disordered surface layer on the particles’ surface, which result into the increased interparticle interactions and enhanced surface anisotropy. These observations are discussed in detail.

Based on a microscopic model, we conducted a systematic theoretical study of the superconducting proximity effect and inverse proximity effect in heterostructures composed of Weyl semimetals (WSMs) and conventional s-wave superconductors. Through self-consistent calculations, we obtained the spatial distribution and symmetry properties of the superconducting order parameters. In the WSMs layer, the ( C_4 ) rotational symmetry and inversion symmetry of the superconducting order parameter are significantly broken, and the singlet-channel order parameter exhibits ( C_4 ) symmetry, containing both s-wave and d-wave components. By calculating the spectral functions and local density of states (LDOS) in the WSMs and conventional s-wave superconductors layers, we provided theoretical predictions that can be used to experimentally probe the proximity effects. In the conventional s-wave superconductors layer, the normal-state Fermi surface undergoes splitting due to interfacial coupling, with the degree of splitting increasing as the coupling strength grows, while an effective spin-orbit interaction term is induced. In the superconducting state, the original s-wave order parameter in the conventional s-wave superconductors is significantly suppressed, its symmetry is broken, and an additional d-wave pairing component is induced. These phenomena can be well understood by analyzing the Fermi surface characteristics of the original systems.

In this work, we investigate the magnetic properties and hysteresis behavior of a mixed spin-1 and spin-7/2 Blume–Capel (BC) Ising model via the mean field approximation (MFA) method, which is based on the Gibbs–Bogoliubov inequality for free energy. We study the system both in the presence and absence of an external magnetic field (h) and explore the appearance of compensation critical points for different crystal field D values when h = 0. The results indicate that there is a critical point of (D_B) = − 2.0, which promotes the appearance of compensation points, whereas (D_A) influences the value of the compensation points. The thermal behavior of the order parameters is analyzed across various crystal field values under multiple external field strengths at specific temperatures. Our results indicate that the system undergoes a second-order phase transition at h = 0, whereas first-order phase transitions occur for h > − 0.5. Only a single hysteresis loop exists for D = 0 and T < 8; however, triple and double hysteresis loops are observed when the crystal field conditions change, along with the emergence of a superparamagnetic phase at higher temperatures and at lower values of D.

The rare earth element-doped barium hexaferrite nanoparticles have drawn great interest towards researchers due to their improved thermal, magnetic, and structural characteristics. These properties make them appropriate for cutting-edge technological applications like shielding against electromagnetic interference, high-density data storage, and microwave absorption. Because of their distinct electronic configurations, rare earth metals like neodymium, strontium, Europium, and lanthanum change thermal stability, coercivity, and magnetic anisotropy when added to the barium hexaferrite lattice. This review examines the different synthesis methods for doping barium hexaferrite with rare earth ions, including sol–gel combustion, ball milling, and co-precipitation procedures, emphasizing the impact on the material’s structural, morphological, and magnetic properties. The different rare earth-doped barium hexaferrite particles resulting in various applications are also covered in this review.

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