Journal of Superconductivity and Novel Magnetism最新文献

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 identification of suitable nanocarriers for drug delivery has been a constant area of research and development. Two-dimensional nanomaterials based on graphene have been presented and proven as drug carriers in this instance. In this study, we employed calculations from density functional theory to examine the electronic and adsorption properties of the commonly administered anticancer medication hydroxyurea (HU) on armchair BN graphene nanoribbons with and without vacancy defects. The band gap of the structures, both with and without the presence of an anticancer drug, exhibits semiconductor behavior, with the exception of ABNNR which initially exhibits insulator behavior with a 6.009 eV energy gap, but upon interaction with the HU molecule, the energy disparity diminished to 4.72 eV. With an E_ads = − 1.079 eV, the adsorption energy of the HU drug molecule on ABNNR-V_N is significantly greater than that of the other complex structures. Based on the computed structural and electronic characteristics, it has been determined that HU/ABNNR-V_N exhibits a greater propensity for HU molecule adsorption in comparison to alternative structures.

Manganites of rare earth elements are currently promising materials for electronics, catalysis, current sources and other applications. Their widespread demand is caused by a variety of structural and magnetic effects connected with substitutions in the sublattices of rare earth element and manganese. Substitutions of rare earth element by Sr, Ca, or Ba in manganites are known to impact the Jahn-Teller (JT) transition temperature as well as the concentration of Mn³⁺ and Mn⁴⁺ ions, which influences the efficiency of double exchange in magnetic orderings. In this work, solid solution Sm_1-xSr_xMnO₃ with low concentrations of the substituting element x = 0; 0.15; 0.25 has been studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal analysis, and magnetometry. Samarium manganites have a perovskite-like orthorhombic structure (Pbnm space group). It has been shown that the Sm-by-Sr substitution leads to a gradual increase in the valence of manganese from 3 + to intermediate value 3.67+. This is accompanied by an increase Néel temperature in (T_N) from 56 K at x = 0 to 90 K at x = 0.25, in the paramagnetic Curie temperature (Θ) from − 30.3 K at x = 0 to 119.9 K at x = 0.25, as well as in the value of the saturation magnetic moment (µ_S) from 0.27 µB at x = 0 to 3.49 µB at x = 0.25. In addition, such substitution leads to a decrease in the temperature of the JT structural transition from 996 ºC at x = 0.0 to 252 ºC at x = 0.25. The relationship between the magnetic properties and the crystal structure of samarium manganites is discussed.

The permanent magnetic properties of Nd-Fe-B magnets strongly depend on the alloy composition. Machine learning is based on mathematical and information science methods and uses existing Nd-Fe-B data to predict the magnetic properties of Nd-Fe-B materials. We use the ensemble learning boosting method to establish the gradient boosting regression tree (GBRT) model for Nd₂Fe₁₄B melt-spun bonded magnets, in comparison with three other methods of machine learning: support vector machine (SVR), multiple linear regression (MLR), and random forest (RFR). The results show that the machine learning GBRT model developed using the ensemble learning algorithm has higher prediction accuracy and better stability than those three traditional machine learning (SVR, MLR, RFR) models used in the past to predict the magnetic properties of melt-spun Nd-Fe-B bonded magnets. We also used the GBRT model to predict hard magnetic properties of melt-spun Nd₂Fe₁₄B/Fe₃B composite materials. Several new alloy compositions of melt-spun Nd-Fe-B bonded magnets and Nd₂Fe₁₄B/Fe₃B composite materials with high-performances were also predicted. Machine learning based on the GBRT model can play an important role in the design, preparation, and development of melt-spun Nd₂Fe₁₄B bonded magnets and Nd₂Fe₁₄B/Fe₃B composite materials.

The crystal structures of type 1234 and 2234 are not found in compositions Bi_1-xB_xSr₂Ca₃Cu₄O_y and Bi_2-xB_xSr₂Ca₃Cu₄O_y after synthesis under conditions of ambient pressure P = 1 bar and T = 835 °C for τ = 240 h. This conclusion is obtained as a result of the fact that the series of bismuth superconductors Bi_1-xB_xSr₂Ca₃Cu₄O_y, Bi_2-xB_xSr₂Ca₃Cu₄O_y, Bi_2-xB_xSr₂Ca₂Cu₃O_y, Bi_1.7-xB_xPb_0.3Sr₂Ca₂Cu₃O_y with different boron content x = 0-2 were synthesized followed by slow (rate < 10 °C/sec) cooling or quenching (< 100 °C/sec). Samples of Bi_1.7-xB_xPb_0.3Sr₂Ca₂Cu₃O_y with a boron content of x = 0.5 have a significant (> 35%) proportion of the superconducting phase 2223, regardless of the accuracy of observing the temperature modes of synthesis (in temperature ranges < ±10 °C) and cooling after it. A model of the effect of boron on phase equilibrium in Bi-Pb-Sr-Ca-Cu-O system is proposed using the process of boron-bismuth glass formation. Therefore, the boron addition during the synthesis of bismuth superconductors will increase the production process reproducibility of phase 2223. Also, this technology can be used at the synthesis of superconductors from the boron-bismuth not very enriched ores in conditions of limited available resources.

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.

Herein, we report a fundamental study revealing the substantial change in magnetic and electrical properties promoted by manganese (Mn) substitution in the iron (Fe) site of double perovskite LaYFe₂O₆ [LaYFe_2-xMn_xO₆; x = 0, 0.05, 0.10, and 0.15], which is prepared by the sol–gel auto-combustion method. The structural, morphological, magnetic, and electrical properties of all the samples are investigated to explore the influence of Mn in the compound. X-ray diffraction (XRD) study reveals the confirmation of phase formation with orthorhombic crystal structure having symmetries P2₁nm and Pbnm (small contribution). X-ray photoelectron spectroscopy (XPS) analysis corroborates the mixed valence state of Fe and Mn, while the dominancy of + 3 oxidation state can be confirmed for them. Magnetization study reveals that the transition temperature reduces drastically (~ 100 K) by the Mn substitution and approaches toward room temperature (RT). At 573 K, the maximum magnetization value enhanced up to ~ 30% by the Mn substitution. Grain boundary contribution in the electrical response is more prominent in the higher Mn content samples. The application of DC magnetic field exhibits a significant influence on the impedance spectra due to the substitution of Mn in the lattice, which corroborates the signature of magnetoelectric (ME) coupling. The presence of ME coupling is further confirmed by the direct magnetoelectric measurement. This finding along with the above RT magnetic transition could make it a feasible candidate for ME-based applications.

In this research, a novel method to improve the particle size and content of Y₂BaCuO₅ (Y-211) in YBa₂Cu₃O_7 − x (YBCO) bulks was demonstrated. The single-domain YBCO bulks (20 mm in diameter) have been fabricated employing the RE+011 TSIG technique with different heating rates during the liquid phase infiltration (LPI) stage. The various heating rates on Y-211 size and its content in the final YBCO samples has been investigated in detail. The findings suggest that the average size of the Y-211 particles in the Y-123 matrix initially decreases followed by an increase, while its volume fraction gradually decreases with increasing heating rate. Furthermore, it is observed that the levitation force and the trapped fields exhibit an initial increase followed by a subsequent decrease as the heating rate increases. Among all the samples, sample S3 (heating rate of 30 °C/h) has the best magnetic levitation force and trapped field performances at 77 K, i.e., the largest values are of 45.3 N and 0.41 T, respectively. The results suggest that, while employing the RE+011 TSIG technique for YBCO bulk fabrication, the average size and volume fraction of Y-211 particles in the final sample can be further enhanced by controlling the heating rates during the LPI stage, obviating any need for chemical refining agents.