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Abstract: Abstract Structural, electrical, elastic, optical, and dynamical properties of LiSiB half-Heusler compound were analyzed based on density functional theory implemented in Quantum Espresso and ABINIT package programs. The effects of exchange–correlation interactions are handled by the generalized gradient approximation with Perdew-Burke-Ernzerhof parametrization. Firstly, the structure of this half-Heusler compound has been optimized and our results indicate that LiSiB reveals semiconducting behavior with an indirect band gap of 0.21 eV. The elastic constants, and other elastic modules have been computed. The mechanical stabilities of these alloys have been theoretically confirmed. The phonon dispersion spectra and phonon density of states in the Brillouin zone have been obtained and discussed. Also, the optical properties were calculated, and the results showed that the LiSiB alloy has a strong optical transition and the LiSiB crystal could be used in the design of optoelectronic devices. There are no results found on elastic, optical, and phonon features of LiSiB in the literature; hence, the findings reported here shed light on future studies. PubDate: 2022-05-21
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Abstract: Abstract Autoresonance is a new non-linear method for excitation of spin subsystem in magnetics by an extremely low magnetic field. Here, we consider the autoresonance (autophasing) process in a model of yttrium iron garnet (YIG) film possessing out-of-plane uniaxial anisotropy. As a result of simulation in MuMax3 software, the parameters of exciting field are determined and a model is proposed for successful auto-phase locking at GHz frequencies. The numerical data obtained for the model with material parameters close to ones for low-damping yttrium iron garnet films are in good agreement with theoretical predictions. It is shown that the process of phase locking leads to a soliton-like character of the excited magnetic oscillations with a high-amplitude of precession. The maximum angle of magnetization deflection reaches up to 150° at the exciting field of 1 mT sweeping with the rate 4.3 × 1016 s−2. It is presented the stability of the autoresonance in the case of low damping in the developed model. Besides, the damping could be used for adjusting the parameters of the autoresonance, which paves the way for potential experimental testing. PubDate: 2022-05-21
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Abstract: Abstract Junction resistance (RN) as a function of temperature (T) in bulk superconducting NdBa2Cu3O7-δ (NBCO) has been determined following the de Gennes (dG) and Ambegaokar–Baratoff (AB) theories. A convergence of RN (T) obtained by two theories is not impossible at a T which is below the critical temperature. Variation of RN (T) corresponding to the intergranular region is very sensitive to the T-dependence of the gap function (Δ). Moderate range of RN reveals that the junctions are SNS in nature. Within the framework of the dG theory, the influence of the correlation length (ξN) on RN has also been investigated. Also, a moderate junction resistance and nonlinear current–voltage (IV) together reveal that a resistive bulk pinning network may be existing near the superconducting phase transition region. PubDate: 2022-05-20
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Abstract: Abstract This article reports an easy route synthesis of bulk polycrystalline TiSe2. Phase purity and micro-structure are determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FESEM) respectively. Vibrational modes of TiSe2 as being analyzed by Raman spectroscopy show the occurrence of both A1g and Eg modes. Charge density wave (CDW) is observed in transport measurements of TiSe2 with a hysteresis in cooling and warming measurements at around 180 K. Furthermore, studied TiSe2 showed negative magnetoresistance (MR) below the CDW and a small positive MR above the CDW. PubDate: 2022-05-20
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Abstract: Abstract Superconducting power transmission is a new type of power transmission technology developed based on the characteristics of superconductors such as zero resistance and high current density. The triaxial structure is more compact and has great advantages in densely populated areas with limited transmission corridors. However, since its three-phase conductors are wound on the same former, their dimensions cannot be the same, resulting in three-phase unbalance. Three-phase unbalance causes differences in current distribution, resulting in a larger voltage difference between phases, which may reduce the current-carrying capacity of the cable. Therefore, the impedance balance design and optimization research of triaxial high-temperature superconducting (HTS) cable have important guiding significance for the development of large-capacity and long-distance superconducting cables. In this paper, the energized conductor is designed for the triaxial HTS cable, and the improved particle swarm algorithm is used for optimization research, and the optimization schemes of the three-phase single-layer and three-phase double-layer structures are compared. The reverse scheme of the single-layer structure can reduce the impedance unbalance to 1%, and the commutation scheme of the two-layer structure can reduce the impedance unbalance to 2% to achieve a three-phase impedance balance. PubDate: 2022-05-20
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Abstract: Abstract For the ultimate goal of adjusting the physical properties of the tin-carbide (SnC) semiconductor, a meticulous theoretical study based on density functional theory (DFT) and Korringa–Kohn–Rostoker (KKR) method combined with coherent potential approximation (CPA) on transition metals substitution is investigated. Iron (Fe) and chromium (Cr) ions have been chosen for their interesting magnetic properties (spin moment, Curie temperature). A value x corresponding to the substitution concentration is varied between 2% and 24% for both \(Sn_{1-x}Cr_{x}C\) and \(Sn_{1-x}Fe_{x}C\) compound types. All \(Sn_{1-x}Fe_{x}C\) compounds show a half-metallic ferromagnetic nature, while a similar behavior is also revealed for \(Sn_{1-x}Cr_{x}C\) compounds with x up to 12. Our self-consistent (SCF) spin-polarized calculations findings revealed that the main contributions to the net magnetization of our compound originate from Fe and Cr ions, with the partial spin moment of Fe is \(3.68\,\mu _{B}\) for \(24\%\) and is around \(2.4\,\mu _{B}\) for Cr. The mean field approximation indicates that the Curie temperature reaches its highest value of 502.86K for Fe at the x-value of 12% , whereas with Cr substitution, the greatest value of 712K is found at x=24%. These findings show that \(Sn_{1-x}Cr_{x}C\) and \(Sn_{1-x}Fe_{x}C\) compounds are promising for spintronics applications. PubDate: 2022-05-19
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Abstract: Abstract Although various methods have been used to prepare Nb3Al superconducting materials to accelerate their commercialization, the preparation of Nb3Al by spark plasma sintering (SPS) is rarely reported. In this paper, Nb3Al superconductors were successfully prepared by SPS technology. By comparing with the traditional powder metallurgy (PM) method, the phase formation mechanism and superconducting properties of SPS-Nb3Al were investigated. The results show that the SPS-Nb3Al has a larger lattice constant similar to the high-temperature melt phase, and its lattice constant is very sensitive to the annealing treatment. It reveals that in SPS process, the local high temperature generated by plasma heating accelerates the formation of Nb3Al phase. In addition, the short reaction time and fast cooling make the Nb3Al grains small and tightly connected. The Al content in SPS-Nb3Al is relatively high, which results in a better superconductivity compared with the PM-Nb3Al. PubDate: 2022-05-19
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Abstract: Abstract The NiO and different concentrations of Ce/Mg-doped NiO were prepared by simple microwave method. For this synthesis, urea is added as a precursor material. The optical, magnetic, and antibacterial properties of the synthesized nanoparticles were investigated. The powdered XRD diffraction pattern gives the structural analysis and also the study revealed that the particles were multi polycrystalline nature. The HRTEM images show that the nanoparticles were homogeneous spherical particles. The UV–visible spectrum shows that while increasing the cerium doping concentration, the band gap energy also increases. The bacterial efficiency of the synthesized samples was analyzed by using Gram-positive and Gram-negative bacteria. PubDate: 2022-05-19
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Abstract: Abstract The phase transitions in the 5-state 3d site-diluted Potts model are investigated by means of the computer simulation methods. We address systems with liner sizes L × L × L = N, L = 20 ÷ 160 at p = 1.00, 0.90, 0.85, and 0.80. Based on the analysis of the fourth-order Binder cumulants and the histogram data analysis, the position of the tricritical point at the phase diagram is determined. PubDate: 2022-05-18
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Abstract: Abstract The structure, magnetic properties, and critical behavior of Nd0.6Sr0.2K0.2MnO3 compound are investigated. Rietveld refinement of the X-ray diffraction pattern shows that the examined sample is a pure single phase, crystallized in an orthorhombic Pnma structure. The nanometric size of crystallites calculated using Williamson-Hall method is validated by transmission electron microscopy micrographs. Magnetic measurements indicate a second-order ferromagnetic (FM)/paramagnetic (PM) transition at the Curie point Tc. Various techniques are used such as modified Arrott plot (MAP), Kouvel-Fisher method (KF), and critical isotherm analysis (CIA) to identify critical properties from isothermal magnetization data near critical regions. The deduced values are close to the 3D Ising model, proving the existence of a short-range ferromagnetic order in Nd0.6Sr0.2K0.2MnO3 sample. The results fully meet the requirements of the universal scaling assumption, further confirming its accuracy. PubDate: 2022-05-18
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Abstract: Abstract The elastocaloric effect and magnetic performance of Ni50Mn31.5Ti18Cu0.5 shape memory alloy were studied. The analysis of magnetic transformation shows that the transformation temperature of the alloy is close to room temperature. A large unloading rate can make the alloy showing smaller hysteresis and lower plastic deformation, and improve the superplasticity of the alloy. With the increase in loading stress, the cooling effect of the alloy is better. When the loading stress is 600 MPa, the ΔT of the alloy reaches 9 K. The alloy has good cycle stability during 100 cycles. Hence, the refrigeration performance of Ni50Mn31.5Ti18Cu0.5 alloy can be compared with many Ni-Mn-based alloys, which indicates that it is a promising elastocaloric refrigeration material. PubDate: 2022-05-16
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Abstract: Abstract Technological conditions under which a two-phase epitaxial thin film of Co is formed on a stepped surface of Si(111)-5.55×5.55-Cu with a buffer layer of Cu(111) and an ordered array of single-crystal nanostrips of hcp-Co with sharp interphase boundaries growing by self-organization were determined. The crystal structure of epitaxial thin films and single-crystal Co nanowires was deciphered by the diffraction methods. Magnetic anisotropy in epitaxial thin films and single-crystal nanostrips of Co was investigated. Using Kerr microscopy, the magnetization reversal modes in epitaxial thin films of Co were studied and discussed. The results presented shed light on the magnetic properties and domain structure depending on the crystal structure and geometry of magnetic nanomaterials promising for racetrack memory. PubDate: 2022-05-16
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Abstract: Abstract In this work, the P-doped FePt films were successfully prepared by electrodeposition and subsequent annealing. Varied NaH2PO2•H2O was added to adjust the content of P in the FePtP film. Crystalline structure, morphologies in micro- and nano-scales, and magnetic property of FePtP films were investigated. The P doping significantly enhances the coercivity in the FePtP films. High coercivity of 23.8 kOe is achieved in the FePtP film with 22 at% P. The P doping promotes the formation of L10 FePt phase. Nonmagnetic Fe2P and PtP2 are formed by the P doping and segregate at grain boundary, which reduces the exchange coupling between magnetic particles. These two factors result in the enhancement of coercivity. PubDate: 2022-05-16
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Abstract: Abstract In this paper, the dynamics of the spin-1/2 Ising model with added DM interaction is studied. We assume DM interaction is a function of the time. We consider one of the Bell states as an initial state. The concurrence is used to analyze the entanglement between two spins. It is found that in the absence of the DM interaction, the entanglement maintains its maximum value. By raising DM interaction, the fluctuations of the entanglement increase. If the DM interaction varies with time, the dynamic behavior of the entanglement will be different. By increasing the amplitude of sinusoidal DM interaction, the entanglement fluctuations will be in the opposite phase in the short term. The combination of the constant and time-dependent DM interactions makes the system generates a series of entanglement revival and collapse phenomena over the time. Increasing the angular frequency of the DM interaction changes the order of the entanglement oscillations and strongly increases the oscillations’ speed. PubDate: 2022-05-14
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Abstract: Abstract La0.5Ag0.1Ca0.4MnO3 manganite nanoparticles are synthesized via two different ways, namely, a solid-state reaction (S1) and the sol–gel process (S2). Their structural, magnetic, and magnetocaloric properties are reported. The powder X-ray diffraction (PXRD) and Rietveld refinement analyses confirm fully crystalline single-phase orthorhombic nanoparticles, even with different conditions of synthetic processes. Moreover, considering the magnetic phase transition of both samples through Banerjee’s criterion revealed a second-order paramagnetic–ferromagnetic phase transition. The influence of elaboration process on magnetic and magnetocaloric behaviors has been investigated. The solid-state sample exhibits a lower magnetic entropy change ( \(\Delta\) SM) value in comparison to that obtained by sol–gel reaction. Besides, the effect of magnetoelastic coupling and electron interaction in magnetocaloric properties was evidenced via Landau theory. PubDate: 2022-05-13
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Abstract: Abstract An analytical formula for the force acting on a spherical superconductor in an external axisymmetric magnetic field is obtained. Its application is illustrated by calculating the force of the action of the magnetic field of a circular loop with current on a superconducting ball. PubDate: 2022-05-12
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Abstract: Abstract According to the importance of electron–phonon interaction, we present an ab initio study of the electron–phonon coupling constant of two superconducting elements of periodic table. These values were calculated using density functional perturbation theory for uranium and lutetium, which are not available in the literatures. The electronic density of states peak that is around the Fermi energy and the sharp peaks in phonon dispersion curve are larger in magnitude for uranium, so the electron–phonon interaction in uranium is higher than that in lutetium. Then, we constructed a model by machine learning approach for 28 superconducting elements of the periodic table and chose the Debye and superconducting transition temperatures as descriptors features, to predict the electron–phonon coupling constants for uranium and lutetium. The absolute (relative) errors between the predicted by machine learning algorithm and density functional theory results of electron–phonon coupling constants are 0.01 (2%) and 0.13 (15%) for uranium and lutetium, respectively. This shows the power of the machine learning approach, which gives the results consistent with the density functional theory’s results. PubDate: 2022-05-12
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Abstract: Abstract The magnetodielectric effect has attracted considerable attention due to its intriguing physics and potential engineering applications in modern data storage, sensors, gyrators, and other novel low power electronic applications. Here, we investigate the dielectric behavior, exchange bias coupling, and magnetodielectric effect in nano-scaled CrO2/Cr2O3 core–shell structures. Importantly, our experiments have revealed interesting results whereupon the magnetodielectric effect and exchange bias coupling are strongly correlated in ferromagnetic and antiferromagnetic structures. It is notable that the magnetodielectric effect at room temperature can be enhanced from 1 to 3.5% with exchange bias coupling. Thus, the magnetodielectric effect is enhanced by as much as 250% with the assistance of exchange bias coupling. Results are interpreted here in terms of a spin-dependent transport model. PubDate: 2022-05-10
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Abstract: Abstract High-temperature superconducting (HTS) maglev, named as the most promising technology of the future transportation, has attracted more and more attention, especially on the dynamic characteristics. In practice, the temperature varying inside the bulk together with the irregularity of the permanent magnetic guideway (PMG) directly and simultaneously affects the levitation and guidance force. This paper takes the HTS bulk, liquid nitrogen (LN), and PMG into account to establish the two-dimensional magnetic-thermal-guideway coupled model by using COMSOL Multiphysics. In order to simulate the magnetic field fluctuation caused by the PMG’s arrangement irregularity, we add the test track irregularity spectrum of high-speed railway to the PMG. The temperature effect on levitation and guidance force is simulated and analyzed under four conditions of excitations as well as comparing with the model without considering the temperature. The results show that the temperature and coupling of excitations in both directions simultaneously affects the magnitude of levitation and guidance force, and the difference caused by above two factors is significant, which makes a better understanding of the relation between the force and temperature and provides an effective reference for the HTS bulk’s dynamic analysis. PubDate: 2022-05-06
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Abstract: Abstract We have theoretically studied the spin structure factors of Heisenberg model on Lieb lattice in the presence of magnetic field along perpendicular to the plane and Dzyaloshinskii–Moriya interaction. The original spin model Hamiltonian is mapped to a bosonic model using a hard-core bosonic transformation. Under such transformation, an infinite hard-core repulsion is imposed to constrain one boson occupation per site. Based on Green’s function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two-particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the peak position in the dynamical transverse spin structure factor at fixed value for Dzyaloshinskii–Moriya interaction moves to higher frequency with enhancement of magnetic field. However, the intensity of peaks in dynamical transverse spin structure factor is not affected by magnetic field. Also the Dzyaloshinskii–Moriya interaction strength causes to increase the intensity of dynamical longitudinal spin structure factor. Also the increase in magnetic field causes to move the frequency position of peaks in dynamical longitudinal spin susceptibility toward low frequencies. Our results show static transverse structure factor is found to be monotonically decreasing with magnetic field. Moreover, a monotonic reduction behavior for temperature dependence of static spin susceptibility has been observed for temperature dependence at each value of Dzyaloshinskii–Moriya interaction strength. PubDate: 2022-05-06
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