Journal of Superconductivity and Novel Magnetism最新文献

ZnO-CuO nanocomposite particles (NCPs) were synthesized at different molar ratios (4:1, 3:2, and 1:4) through the use of the co-precipitation technique, which produced interesting modifications in the particle’s physical characteristics. XRD showed that average crystallite size (D_avg) decreased noticeably from about 22.07 to 15.98 nm as the concentration of CuO increased within the ZnO matrix. This pattern points to a major impact of CuO content on the composite’s structural properties. Fourier-transform infrared spectroscopy (FTIR), two distinct functional groups were identified: v₁ and v₂, which were detected at approximately 524 cm⁻¹ and 427 cm⁻¹, respectively, and were linked to intrinsic and extrinsic vibrations. These spectral characteristics highlight the complex interaction between ZnO and CuO and offer important insights into the chemical bonding and molecular interactions within the composite system. The ZnO-CuO nanocomposite was subjected to field emission scanning electron microscopy and energy-dispersive X-ray analysis (SEM-EDX) which showed spherical shapes with increments in agglomeration. UV-Vis absorption spectra revealed a blue shift with increasing absorption in the UV region. The energy band gap of ZnO in its pristine state was found to be 3.31 eV, but in the ZnO₄-CuO₁ composition, it increased to 5.48 eV, suggesting that the addition of CuO caused a significant change in the electronic structure. Significantly, ZnO-CuO NCP antimicrobial evaluation demonstrated exceptional antibacterial efficacy against bacterial strains that were both Gram positive and Gram negative, in addition to fungal pathogens. This strong antimicrobial activity highlights the synthetic nanocomposite’s potential use in fighting a range of microbial infections and highlights their bright future in the environmental and biomedical fields.

In this paper, we have investigated the magnetic and magnetocaloric characteristics of a La₂MnNiO₆ composite, in conjunction with La₂MnCoO₆. This composite consists of two phases of double perovskite materials. Employing the mean-field approximation, we successfully modeled how magnetization and the change in magnetic entropy vary with temperature under different magnetic fields in our samples. This phenomenological model helped us also plot the maximum magnetic entropy change (-ΔS_M)_max, full width at half-maximum δT_FWHM, and relative cooling power (RCP). Our analysis has revealed an optimal plateau-type magnetocaloric effect near room temperature, corresponding to a specific composition x between 0.2 and 0.5. Ultimately, this theoretical model lets us predict the magnetic and magnetocaloric behavior of composite materials, providing a foundation for future studies.

The perovskite La₂ZnMnO₆ was successfully synthesised using the conventional solid-state reaction. X-ray diffraction shows that the perovskite La₂ZnMnO₆ crystallizes in a monoclinic structure P2₁/n space group, where Zn and Mn atoms are regularly distributed. The Raman spectrum result reveals three peaks at 696 cm⁻¹, 655 cm⁻¹ and 505 cm⁻¹, corresponding to the A_g stretching mode, B_g anti-stretching, and bending vibrations modes of Ni/Co-O and Mn-O bonds in the structure. The experimental value of the band gap energy was calculated using Tauc’s formula and the result reveals a semiconducting behaviour. We investigated the structural, elastic, magnetic, and electronic properties using the spin-polarized density functional theory. The partial density of state indicates that the material exhibits a antiferromagnetic semiconducting behaviour. The antiferromagnetic ordering is explained by the super-exchange interaction between empty e_g orbitals of Mn⁴⁺( ({t}_{2 g}^{3})({e}_{g}^{0})). The obtained Neel temperature is T_N ∼ 28 K which is comparable with the experiment results. Elastic constants and their derivative parameters show a high mechanical stability of this material with a ductile nature. The investigation of the transport properties encompassed an analysis of the electrical conductivity, the figure of merit, the Seebeck coefficient, and thermal conductivity. The results show that electronic and thermal conductivities increase linearly with temperature. The computed values of the figure of merit are close to unity, suggesting that this material is a promising candidate for thermoelectric application.

It is shown that many anomalies observed in underdoped cuprates, including anomalous spectral weight transfer and a large pseudogap, appear to have a common nature due to both the cluster structure of the underdoped phase and the specific mechanism of superconducting pairing. The combined action of these factors leads to the fact that at a temperature T lying in a certain temperature range T_c < T < T*, the crystal contains small isolated clusters that can exist both in superconducting and normal states, randomly switching between them. In this case, below T_c with a very high probability, the cluster is in a superconducting state, and above T*, it is in a normal state, and the interval T_c < T < T* is the region of existence of the so-called pseudogap phase. The temperatures T_c and T* for YBa₂Cu₃O_6+δ were calculated depending on the doping level δ. The calculation results are in good agreement with the experiment without the use of fitting parameters. At a given T in the same temperature range, the time sequence of randomly arising superfluid density pulses from each cluster can be represented as a random process. The effective width Δω_eff of the spectrum of such a random process will be determined by a correlation time, i.e., the characteristic time between successive on/off superconductivity in two different clusters. This time, according to the estimate, is ~ 10⁻¹⁵ s, which corresponds to Δω_eff ~ 1 eV and explains the effect of spectral weight transfer to the high-frequency region. This approach also makes it possible to explain other anomalies observed in the vicinity of T_c: the reversibility of magnetization curves in a certain temperature range below T_c, the anomalous Nernst effect, and anomalous diamagnetism above T_c.

The surface properties of ultra-thin flaky FeSiAl alloy powders with a thickness of 0.65 μm were modified through a high-temperature reduction process. The original FeSiAl alloy powders exhibited an inherent outer layer primarily composed of FeO_x, SiAl_xO_y, and Al₂O₃. The reduction process involved the reduction of Fe³⁺ to metallic Fe through the use of H₂. During the pressing process of the magnetic core, the flaky FeSiAl alloy powders naturally formed a stack structure with the (100) orientation. Following the reduction treatment, the FeSiAl magnetic core demonstrated an effective permeability as high as 624 at 100 kHz, with a total loss of 108.8 mW/cm³ under maximal applied fields of 50 mT at 100 kHz. These results reveal that high-temperature reduction treatment and reduction in the thickness of flaky FeSiAl alloy powders play the significant role in further enhancing their magnetic core properties.