Showing papers in "Journal of Superconductivity and Novel Magnetism in 2017"

Room-Temperature Superparamagnetism and Enhanced Photocatalytic Activity of Magnetically Reusable Spinel ZnFe 2 O 4 Nanocatalysts

Abstract: Spinel ZnFe2O4 nanoparticles (NPs) were successfully synthesized by a simple microwave irradiation method (MIM) using glycine as the fuel. For the comparative study purpose, it was also prepared by a conventional heating (CHM) method. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), high-resolution scanning electron microscope (HR-SEM), high-resolution transmission electron microscope (HR-TEM), energy-dispersive X-ray (EDX) spectra, and selected area electron diffraction (SAED) analysis showed that the samples were pure-phase spinel ZnFe2O4 nanoparticle-like morphology without any other secondary-phase impurity. UV-Visible diffuse reflectance spectra (DRS) and room temperature photoluminescence (PL) spectra confirmed the optical band gap (E g) and defect state of the samples. The calculated E g values of the samples are 1.98 and 2.11 eV for ZnFe2O4-CHM and ZnFe2O4-MIM, respectively. Vibrating sample magnetometer (VSM) analysis shows that the M s value is 37.66 emu/g for ZnFe2O4-MIM, which is higher than the ZnFe2O4-CHM (24.23 emu/g) sample, which confirms that both the products showed a superparamagnetic behavior. ZnFe2O4-MIM was found to have a higher surface area than ZnFe2O4-CHM, which in turn leads to the improved performance towards the photocatalytic degradation (PCD) of methylene blue (MB), and it was found that the sample ZnFe2O4-MIM shows a higher PCD efficiency (91.43%) than ZnFe2O4-CHM (84.65%); also, the samples show high activity, good reusability, remarkable stability, and environmentally friendly materials for industrial and technological applications.

First-principles Calculations of Structural, Magnetic Electronic and Optical Properties of Rare-earth Metals TbX (X=N, O, S, Se)

Abstract: The structural, magnetic, electronic and optical properties of Terbium-based binaries (TbX) (X = N, O, S and Se) in two cubic structures NaCl and CsCl have been investigated. This study is carried out by Full-Potential linearized Muffin-Tin orbitals (FP-LMTO) method in the framework of the functional theory of density (DFT) implemented in the lmtart code. The presence of f-state electrons in these induced high-correlation materials led us to study these systems using local density approximation (LDA) for the paramagnetic state and spin local density approximation (LSDA) for the ferromagnetic state within two cubic structures. We have demonstrated that these binaries are stable in the ferromagnetic state in the cubic phase of NaCl, which allows us to deduce the magnetic moments of these components. From the electronic band structures and density states, we have concluded that TbX (X = N, O, S and Se) are metallic in the NaCl phase. The results obtained in this work show that the theoretical parameters of the ground state, structure of the bands, density of the states (DOS) and optical properties agree well with other available theoretical and experimental data.

Novel Synthesis of Spinel MnxCo1−xAl2O4 (x = 0.0 to 1.0) Nanocatalysts: Effect of Mn2+ Doping on Structural, Morphological, and Opto-Magnetic Properties

Abstract: In this present study, Mn2+doped CoAl2O4 (MnxCo1−xAl2O4; x = 0.0 to 1.0) spinel nanoparticles were synthesized by microwave combustion method using nitrates of Co, Mn, and Al as the starting materials and urea was used as the fuel. The effects of Mn2+ doping on structural, morphological, opto-magnetic and catalytic properties were studied. Powder X-ray diffraction analysis was confirmed the formation of cubic spinel aluminate structure. Debye-Scherrer’s formula was used to estimate the average crystallite size of the samples and was found to be in the range of 18.26 to 21.47 nm. It was observed that the calculated lattice parameter value is increased from 8.215 to 8.247 A with increasing the Mn2+ content due to the higher ionic radius of Mn2+ ion. High resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analysis confirmed the nano-sized particle-like morphology of the samples. Energy dispersive X-ray (EDX) results showed the pure form of spinel aluminate structure. The band gap energy (Eg) of undoped CoAl2O4 was estimated to be 3.58 eV from UV-visible diffuse reflectance spectroscopy (DRS), and the Eg values increased with increase of Mn2+ ions due to the decrease of grain size. The magnetic hysteresis (M-H) loop showed the superparamagnetic nature of the samples, and the saturation magnetization values increased with increasing Mn2+ ions, which was confirmed by vibrating sample magnetometer (VSM). All compositions of the samples were successfully tested as catalyst for the conversion of benzyl alcohol into benzaldehyde and observed good catalytic activity.

Doping-Induced Half-Metallic Ferromagnetism in Vanadium and Chromium-Doped Alkali Oxides K2O and Rb2O: Ab Initio Method

Abstract: The electronic structures and magnetic properties of K2O and Rb2O alloys doped simultaneously with Cr and V transition elements were investigated using the full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method within the spin-polarized density functional theory (Spin-DFT) and implemented in the WIEN2k package, where the exchange-correlation potential in this approach is described by the generalized gradient approximation with Coulomb repulsion (GGA + U). The substitution of transition metals at 25 % ratio yields the magnetic characteristic of half-metallic ferromagnetism for K2O and Rb2O alloys. The structural properties were estimated in both magnetic and non-magnetic phases, demonstrating the stable ferromagnetic ground phase. The analysis of the electronic structure reveals the excellent half-metallic ferromagnetic nature, with a clear half-metallic gap (E HM) of 0.20 eV for K1.75Cr0.25O alloy. The exploitation of the electronic structure mainly served to determine the spin-polarized exchange-splitting energies Δ x (d) and Δ x (pd) generated by 3d-TM states, shows that the effective potential of the minority spin is more attractive than that of the majority spin. Moreover, the s−d exchange constant N 0 α (conduction band) and p−d exchange constant N 0 β (valence band) describe their contributions during the exchange splitting process. The magnetic properties have indicated that these alloys acquire a magnetic moment when the non-magnetic system is doped with a transition metal (TM). The obtained results from the important magnetic moments of these alloys indicate the potential for their use in spintronic devices.

Electronic and Magnetic Properties of Co2CrGa1−xSix Heusler Alloys

Abstract: First-principles calculations within full-potential linear-augmented plane-wave method using the generalized gradient approximation were carried out for the electronic and magnetic properties of the Co2CrGa1−x Si x Heusler alloys. The electronic structure calculations show a conservation of the minority spin gap supporting the half-metallic character of the Co2CrGa1−x Si x alloys. The substitution of Ga by Si results in linear increasing of total magnetic moment as silicon concentration increases following the Slater–Pauling rule that is in agreement with experimental data.

Ab Initio Investigations of Structural, Elastic, Mechanical, Electronic, Magnetic, and Optical Properties of Half-Heusler Compounds RhCrZ (Z = Si, Ge)

Abstract: The first principle study of half-Heusler compounds RhCrZ (Z = Si, Ge) is performed in the framework of density functional theory (DFT). The compounds are found to have small band gap in the minority spin channel (spin-down). While the majority spin channel (spin-up) is metallic. Therefore, both compounds are half-metallic and 100 % spin polarized at Fermi level. Several properties including structural, mechanical, elastic, electronic, magnetic, and optical are computed using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2k simulation package. Equilibrium lattice constants for both compounds are found to be in the range 5.5–6.0 A. Elastic properties indicate the ductile nature of the compounds. The total magnetic moments for these compounds are approximately equal to 1μ B, i.e., MTot ≈ 1μ B. Hence, the compounds are weak ferromagnetic materials. We have calculated the complex dielectric function. Many optical properties including reflectivity, refractive index, conductivity, and absorption coefficients are obtained form dielectric function. Imaginary part of the dielectric functions shows that compounds are optically metallic and become transparent above 17 and 13 eV, respectively. It is also observed that compounds are more active in the infrared region.

A First-Principles Calculation on Structural, Electronic, Magnetic, Mechanical, and Thermodynamic Properties of SrAmO3

Abstract: For the first time, the americium-based perovskite SrAmO3 has been studied with respect to its structural, electronic, magnetic, mechanical, and thermodynamic properties The study has been carried within the well-known density functional theory (DFT) using different approximations such as local spin density approximation (LSDA), generalized gradient approximation (GGA), LSDA + U, GGA + U In order to check for the stable ground state, optimization was performed for non-magnetic, ferromagnetic, and anti-ferromagnetic phases, and the compound was found to be stable in the ferromagnetic phase The spin magnetic moment was obtained with different exchange correlations and was found to be an integer which is one of the consequences of half-metallic nature The half-metallic nature of SrAmO3 was also confirmed from spin-polarised band structure calculations using GGA, GGA + U, and mBJ, showing metallic nature in spin-up states and semi-conducting in spin-down states The elastic constants, Young modulus, shear modulus, Poisson ratio, and anisotropic factor were also calculated SrAmO3 was found to establish ductile and anisotropic nature Debye temperature was predicted to be 353 K from elastic constants The thermodynamic properties, like variation of specific heat capacity, thermal expansion, and entropy, were studied in the temperature range of 0 to 600 K

Study of RKKY Interactions in a Bilayer Graphene Structure with Non-equivalent Planes

Abstract: In this paper, we study the magnetic properties and the effect of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in a bilayer graphene structure with non-equivalent planes of a ferromagnetic consisting of the spins σ = 1 / 2 and S = 1. The studied system is formed by two magnetic planes (A and B), separated by a number of non-magnetic planes. In fact, the influence of the coupling exchange interactions, the external magnetic field, and the crystal field is investigated and presented as well as the ground-state phase diagrams. Using Monte Carlo simulations, we examine the behavior of the magnetizations and the total magnetization as a function of the values of system parameters. The effect of the RKKY interactions increases for increasing values of the number of non-magnetic planes; for this reason, the studied system becomes disorder when the number of non-magnetic planes increased. When the susceptibility peaks correspond to the reduced critical temperature (T / J A), this critical temperature is displaced towards the lower temperatures.

Structural and Magnetic Studies of Nano-crystalline Ferrites MFe2O4 (M = Zn, Ni, Cu, and Co) Synthesized Via Citrate Gel Autocombustion Method

Abstract: Nano-crystalline ferrites with the chemical formula MFe2O4 (M = Zn, Ni, Cu, and Co) were synthesized via autocombustion route with citric acid as fuel The ratio of citric acid to metal nitrate was taken as 1:1 The synthesized samples were characterized by powder X-ray diffraction and far-IR spectroscopy The measured lattice constants and observed characteristic IR absorption bands of all samples were in good agreement with the reported values and showed the formation of a cubic spinel structure The crystallite sizes of all samples were determined using high-intensity peaks and a W-H plot The crystallite sizes of all samples were observed to be in the range of 16–26 nm with the least crystallite size of 168 nm for copper ferrite All structural parameters were calculated using an experimental lattice constant and an oxygen positional parameter and correlated with far-IR results Zinc and copper owing to their large cation radii showed the expansion of the lattice in view of the oxygen positional parameter Magnetic measurements were carried out using a vibrating sample magnetometer at room temperature, and parameters such as saturation magnetization, coercivity, remanence, squareness ratio, and Bohr magnetons were calculated Among all synthesized nano-ferrites, cobalt nano-ferrite showed the highest saturation magnetization of 41 emu/g, whereas zinc ferrite displayed a low saturation magnetization value of 1287 emu/g

M-Type Strontium Hexaferrite Nanoparticles Prepared by Sol-Gel Auto-combustion Method: The Role of Co Substitution in Structural, Morphological, and Magnetic Properties

Abstract: In this work, the sol-gel auto-combustion method has been successfully used to prepare nanocrystalline strontium hexaferrite doped with cobalt at iron sites (SrFe12−x Cox O 19, x = 0–1). The crystal structure, morphology, and magnetic properties of samples were systematically investigated using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM), respectively. The three vibrational modes were observed in the FT-IR spectra of calcined samples, which indicated the presence of metal-oxygen stretching bands in hexaferrite structure after calcination treatment. The XRD results confirmed the single-phase M-type hexagonal structure for SrFe12−x Cox O 19 samples with x≤ 0.5; however, for the samples with x> 0.5, the cubic CoFe2 O 4 phase was also appeared. The average particle size determined by TEM analysis was found to be about 87 nm (for x = 0) and 110 nm (for x = 1) whereas the cobalt substitution leads to the larger particles. The saturation magnetization increased with cobalt content up to x = 0.5 and then decreased slowly on further increase of the dopant concentration, while the coercivity decreased continuously with increasing Co content.

Structural and Dielectric Properties of Copper-Substituted Mg–Zn Spinel Ferrites

Abstract: Copper ferrite-doped magnesium zinc ferrite, i.e., Mg0.5Zn0.5−x Cu x Fe2 O 4 (0.0 ≤ x ≤ 0.5) has been synthesized by conventional solid-state reaction technique. The role of copper ion substitution on the crystal and lattice structure and also on the dielectric properties of Mg0.5Zn0.5Fe2 O 4 ferrite is studied. XRD investigation exposes that the synthesized samples are polycrystalline single-phase cubic spinel in structure without the occurrence of any secondary phase corresponding to any structure. Small deviation in the lattice parameter from 8.412 to 8.374 A of copper-doped Mg0.5Zn0.5Fe2 O 4 has been observed due to difference in ionic radii of cations with increase in copper doping. Small shift in Raman modes towards higher wavenumber has been observed with Cu doping. Room-temperature dielectric properties show that for each sample, the dielectric constant decreases with an increase of frequency and becomes constant at higher frequencies. Dielectric loss decreases with increase in Cu concentration. The dielectric constant increases to a great extent in prepared samples.

Particularities of the Magnetic State of CuO Nanoparticles Produced by Low-Pressure Plasma Arc Discharge

Abstract: Copper oxide nanoparticles were produced by direct plasmachemical synthesis in a plasma arc discharge of low pressure. The formation of CuO nanoparticles with an average size of 12 nm and narrow size distribution intervals was determined by using the x-ray diffraction analysis and TEM microscopy methods. It was defined by using a vibration magnetometer and a SQUID magnetometer, that the magnetic properties of CuO nanoparticles with such size were extremely different from the magnetic properties of bulk antiferromagnetic CuO. Structural defects caused the formation of a ferromagnetic state, remaining at least up to the room temperature. The temperature of corresponding antiferromagnetic ordering was significantly decreased (down to ∼ 100 K). Meanwhile, some of the copper surface spins showed a spin-glass behavior at low temperatures.

Overlapping Large Polaron Conductivity Mechanism and Dielectric Properties of Al0.2Cd0.8Fe2O4 Ferrite Nanocomposite

Abstract: In this work, the conduction and dielectric properties of Al0.2Cd0.8Fe2O4 ferrite nanoparticle, which was synthesized by a co-precipitation method, were investigated. Experimental data were taken from 20 Hz to 10 MHz and from 293 to 613 K. AC conductivity of the sample was analyzed within the framework of the overlapping large polaron tunneling (OLPT) mechanism. DC conductivity behavior fits the classical Arrhenius-type conductivity in the examined temperature range. Electrical properties of the material sample have been studied using an impedance spectroscopy technique. The effect of frequency and temperature on dielectric constant (e ′), dielectric loss (tan 𝜃), and impedance (Z′ and Z′′) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. According to results, a relaxation process fits the Cole–Cole model.

Magnetocaloric Properties of Zinc-Nickel Ferrites Around Room Temperature

Abstract: In this paper, structural, magnetic, and magnetocaloric properties of zinc-doped nickel ferrite, Zn1−xNixFe2O4 (x= 0.3 and 0.4) were investigated. The samples were prepared using solid-state reaction. X-ray diffraction (XRD) and magnetization measurements were performed to study crystallographic structure and magnetic properties. For a magnetic field changing from 0 to 5 T, the corresponding isothermal entropy change was found to be near 1.4 J/kg K for both samples. The decreasing of Ni content from x= 0.4 to 0.3, enables to shift the Curie temperature of Zn1−xNixFe2O4 from 450 K toward (325 K). As main results, it was found that the relative cooling power (RCP) could be significantly enhanced by changing Ni concentration in Zn1−xNixFe2O4 (505 J/kg (for x= 0.3) and 670 J/kg (for x= 0.4)), which is considered as a recommended parameter for a wide temperature range in magnetic refrigeration application. Our finding should inspire and open new ways for the enhancement of the magnetocaloric effect in spinel ferrite-based materials.

The Reflection of Cr/Fe Substitution on the Structural, Magnetic and Photoluminescence Features of Zn–Ni Based Ferrite

Abstract: In this work, we substituted iron by chromium in the nano-spinel ferrite Ni0.5Zn0.5Fe2O4 (NZF), then we studied how relevant the structure, magnetic, and optical characteristics of the produced samples are changed accordingly. This doping caused a redistribution of Fe, Zn, and Ni ions over tetrahedral and octahedral sites as confirmed from XRD Reitveld analysis. Upon Cr/Fe substitution, a decrease in the lattice parameter occurred accompanied by a decrease in crystallite size of the doped samples. Magnetic measurements indicated the decrease of saturation magnetization by increasing the amount of Cr doping. On the other hand, the coercivity (H c) increases about six times from Cr content x = 0.0 (28.28 Oe) to x = 1.0 (192.25 Oe). Photoluminescence (PL) measurements at 650 nm excitation showed emission peaks arising from Fe3+ transitions, band-to-band transitions, oxygen defect-related emission, and Cr3+ transitions that appeared strongly at heavily doped NZF with Cr. The PL intensity quenches strongly with increasing Cr/Fe ratio due to concentration, mobility, and generation of non-radiative center effects. The band gap energy of the Cr-doped NZF system is red shifted until x = 0.5 and the increases (blue shifted) at x = 0.75.

Characteristics of Fe3O4, α -Fe2O3, and γ-Fe2O3 Nanoparticles as Suitable Candidates in the Field of Nanomedicine

Abstract: Some items such as toxicity properties and magnetization cause researchers to try to find a favorable magnetic material in the area of cyborg. For this aim, Fe3O4 (magnetite) α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite) as a good option were synthesized and characterized by using fieldemission scanning electron microscopy (FE-SEM), energy dispersion x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV) techniques. The magnetic properties were measured by vibrating sample magnetometer (VSM) technique The obtained results show that with decreasing the half maximal inhibitory concentration (IC50) and size the toxicity of nanoparticles increases. The obtained results show that Fe3O4, α-Fe2O3 and γFe2O3 nanoparticles can be considered as a suitable candidate in medical applications.

Back to Mechanisms of Superconductivity in Low-Doped Strontium Titanate

Abstract: We have analyzed two mechanisms proposed recently for superconductivity in doped SrTiO3 - the plasmon-mediated pairing and the potential of an instantaneous attraction between two electrons that owes its origin to the exchange by high-frequency optical phonons. The first approach seems to be self-consistent, but in a limited range of the dielectric constant. As to the direct instantaneous interaction between two electrons,it was hypothesized as due to the exchange by the band LO phonons. The latter supposition was incorrect. In the current paper, it shows that the contributions into the pairing matrix element possessing the structure of a net attraction come about only as the result of disorder. Indeed, the experiment revealed the mobility edge in doped SrTiO3. Doped electrons occupying states with the energy below the mobility edge are localized on dopants thereby become strongly coupled with the lattice vibrations. The emergence of the localized phonon modes attached to defect is one of the results of such electron-lattice coupling. For two electrons in the conduction band the virtual exchange by the quantum of such local mode manifests itself as the effective attraction. The total contribution into the pairing matrix element from these processes, increasing with concentration can overwhelm the Coulomb repulsion screened by the band LO phonons. That is, the role previously ascribed to the band LO phonons actually belongs to the localized phonons.

Structural, Electronic and Magnetic Properties of NaKZ (Z = N, P, As, and Sb) Half-Heusler Compounds: a First-Principles study

Abstract: The electronic and magnetic properties of the half-Heusler compounds of NaKZ (Z = N, P, As, and Sb) are investigated on the basis of density functional theory. The spin-polarized calculations indicate that these materials are half-metallic ferromagnets with an integer magnetic moment of 1 μ B at their equilibrium lattice constants. The mechanism that leads to half-metallicity in these materials is also investigated. It is found that these compounds are half-metallic ferromagnets on a wide range of lattice constants, and as a result, they could be used in the spintronic devices that contain heterojunctions of half-metal/semiconductors. The Curie temperatures of NaKN, NaKP, NaKAs, and NaKSb are estimated to be 526.3, 494.7, 475.9, and 358.1 K in the mean field approximation, respectively.

Spin Compensation Temperatures in the Monte Carlo Study of a Mixed Spin-3/2 and Spin-1/2 Ising Ferrimagnetic System

Abstract: The magnetic properties of mixed-spin S ′ = 3/2 and S = 1/2 ferrimagnetic system have been studied by Monte Carlo simulations. The ground-state phase diagrams of mixed spin-3/2 and spin-1/2 Ising system are given. The critical and compensation temperatures have been found with different values of reduced exchange interactions. The variation of total magnetization with reduced exchange interactions of mixed spins is given with different temperatures and crystal fields. We have also given the variation of total magnetization with crystal field for different reduced exchange interactions and different temperatures. The magnetic hysteresis cycle is found to have different values of reduced exchange interactions, temperatures, and crystal fields. The multiple hysteresis and the superparamagnetic phase are established.

Electronic and Ferromagnetic Properties of 3d(V)-Doped (BaS) Barium Sulfide

Abstract: The objective of this study is to investigate the electronic structure and ferromagnetic properties of barium sulfide (BaS) doped with vanadium (V) impurity. The calculations were performed by using the first-principle calculations of density functional theory. The lattice constant of Ba1−x V x S decreases with increasing concentration (x) of the V atom. We have found that the Ba0.75 V 0.25S and Ba0.5 V 0.5S compounds are half-metallic ferromagnets with total magnetic moments of 3 μ B per V atom, while for high concentration x = 0.75, the Ba0.25 V 0.75S becomes nearly half metallic due to broadening of 3d (V) states in the gap. The exchange coupling between the 3d (V) levels and conduction bands is ferromagnetic, confirming the magnetic nature of Ba1−x V x S compounds.

Magnetic, Micro-structural, and Optical Properties of Hexaferrite, BaFe12O19 Materials Synthesized by Salt Flux-Assisted Method

Abstract: This paper reports the eco-friendly synthesized BaFe12O19 phase materials by a molten salt flux approach and their experimental findings. The reaction mixture (BaCO3 and Fe2 O 3) annealed with the mixture of salt (NaCl:KCl) flux yielded good quality nanocrystalline hexagonal ferrite BaFe12O19 phase materials. The plate-like hexagonal-shaped BaFe12O19 phase morphology with random particle sizes of ∼370 to 940 nm is seen for the good quality flux-annealed sample. The room-temperature magnetic hysteresis loop of the BaFe12O19 sample exhibits hard ferromagnetic saturation magnetization (M s) of 50.23 emu/g at 15 kOe, and coercive field (H c) is 3500 Oe. The determined energy bandgap (E g) is found to be 3.58 eV for the BaFe12O19 phase material. The Fourier transform infrared (FT-IR) spectral features confirm the presence of Fe–O and Ba–O bonds in the flux-synthesized BaFe12O19 materials. The photoluminescence (PL) emission peak (∼360 nm) intensity of BaFe12O19 materials varies regardless of annealing temperatures. The different salt flux-synthesized BaFe12O19 materials appear as brown- and dark gray-colored powders that can be applied as a ceramic color pigment due to its high NIR reflectivity.

An Experimental Investigation of the Transient Response of HTS Non-insulation Coil

Abstract: A single pancake coil without turn-to-turn insulation was tested in this paper to investigate the transient responses under different situations. We performed charging and discharging test, AC current test, and regional quench emulation test on the non-insulated (NI) coil. The experimental test results show a significant time delay for charging and discharging characteristics of NI coil and can be validated by a simple proposed equivalent electrical circuit. Under the AC operating current, the NI coil can bypass nearly all the AC current from the coil spiral path to the radial path such that it is not possible for NI coil to store or be affected by the AC magnet field. Additionally, while carrying AC current, the AC loss dissipation of NI coil is inversely proportional to the frequency of the AC operating current. When a regional quench occurs, the NI coil can bypass the current in the regional quench zone to avoid further temperature accumulated and protect the NI coil itself.

Synthesis and Magnetic Properties Evaluation of Monosized FeCo Alloy Nanoparticles Through Microemulsion Method

Abstract: In this study, the microemulsion method as a facile and promising synthesis method was employed in order to prepare magnetic FeCo alloy nanoparticles with several Fe/Co weight ratio. For this purpose, a micellar system was applied and the reaction of Fe and Co salts reduction was proceeded in the confined spaces in liquid phase. The electromagnetic waves absorption test was conducted to determine the optimum absorbent sample. The results showed that the sample of prepared in the weight ratio of 70:30 possesses a uniform spherical morphology with an average particle size of less than 10 nm. Furthermore, AFM micrograph confirmed the formation of non-agglomerated uniform spherical nanoparticles. The evaluation of magnetic property of the synthesized samples showed that Fe70Co30 nanoparticles dedicated the highest magnetic saturation of 115 emu g−1. In addition, The magnitude of electromagnetic absorption (return loss) of this sample was measured to be −8.1 dB at 16 GHz which was at the lowest level compared with other samples highlighting the significant effect of Fe/Co weight ratio on final magnetic properties of the alloy system.

Electrical, Thermal and Spectroscopic Characterization of Bulk Bi2Se3 Topological Insulator

Abstract: We report the electrical (angular magnetoresistance and Hall), thermal (heat capacity) and spectroscopic (Raman, X-ray photoelectron, angle-resolved photoelectron) characterization of a bulk Bi2Se3 topological insulator, which was grown by self-flux method through solid-state reaction from high-temperature (950. degrees C) melt and slow cooling (2. degrees C/h) of constituent elements. Bi2Se3 exhibited metallic behaviour down to 5 K. Magnetotransport measurements revealed linear up to 400 and 30% magneto-resistance (MR) at 5 K under a 14-T field in perpendicular and parallel field directions, respectively. We noticed that the MR of Bi2Se3 is very sensitive to the angle of the applied field. The MR is maximum when the field is normal to the sample surface, while it is minimum when the field is parallel. The Hall coefficient (RH) is seen nearly invariant with a negative carrier sign down to 5 K albeit having near-periodic oscillations above 100 K. The heat capacity (C-p) versus temperature plot is seen without any phase transitions down to 5 K and is well fitted (Cp =gamma T + beta T-3) at low temperature with a calculated Debye temperature (theta(D)) value of 105.5 K. Clear Raman peaks are seen at 72, 131 and 177 cm(-1) corresponding to A(1g)(1), E-g(2) and A(1g)(2), respectively. Though two distinct asymmetric characteristic peak shapes are seen for Bi 4f(7/2) and Bi 4f(5/2), the Se 3d region is found to be broad, displaying the overlapping of spin-orbit components of the same. Angle-resolved photoemission spectroscopy (ARPES) data of Bi2Se3 revealed distinctly the bulk conduction bands (BCB), surface state (SS), Dirac point (DP) and bulk valence bands (BVB), and 3D bulk conduction signatures are clearly seen. Summarily, a host of physical properties for the as-grown Bi2Se3 crystal are reported here.

GGA and GGA + U Study of Rare Earth-Based Perovskites in Cubic Phase

Abstract: The structural, elastic, electronic, and magnetic properties of cubic perovskite RAlO3 (R = Sm, Eu, Gd, Dy, Tb, Ho, Tm, Er, Yb) compounds have been calculated using a full-potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The exchange-correlation potential was treated with the generalized gradient approximation of Wu and Cohen (WC-GGA) to calculate the total energy. Moreover, the GGA + U−based potential was also applied for the electronic and magnetic properties. The calculated structural properties such as lattice parameter are consistent with the accessible data. The spin-polarized electronic band structure and the calculation of density of state show that DyAlO3, EuAlO3, SmAlo3, TmAlO3, HoAlO3, YbAlO3, and TbAlO3 compounds have a half-metallic nature, and only GdAlO3 and ErAlO3 have a semiconductor nature. The spin-polarized magnetic moment of these compounds reveals that they show a ferromagnetic nature.

Influence of Al Substitution on Structural, Dielectric and Magnetic Properties of M-type Barium Hexaferrite

Abstract: Polycrystalline Al-substituted BaFe12O19 samples were synthesized and investigated in order to study their structural, dielectric, and magnetic properties. Analysis of powder X-ray diffractions by Rietveld refinement shows the single-phase nature of samples with hexagonal structure. The magnetic properties of the samples were investigated by measuring temperature and field variations of magnetization using vibrating sample magnetometer. The temperature variation of magnetization measurement shows that all samples exhibit ferrimagnetic transition, and the transition temperature is found to decrease from 720 K for x = 0 to 709 K for x = 0.08. The saturation magnetization value at room temperature is found to decrease with increase in Al concentration, and on the other hand, the coercivity is found to increase. The dielectric spectrum of pure and Al-doped samples shows the typical exponential fall in dielectric constant with increase in frequency. The magnitude of dielectric constant at 100 Hz falls from 2000 for x = 0 to 400 for x = 0.10. The permeability spectrum of Al-doped samples is found to be almost independent of frequency for f>100 MHz.

Evolution of Phononic Band Gaps in One-Dimensional Phononic Crystals that Incorporate High-T c Superconductor and Magnetostrictive Materials

Abstract: In this work, we calculate the reflectance of one-dimensional phononic crystals (1D PnCs) using the transfer matrix method. We present numerical results for two different PnC structures, the first one, PnCs1, contains high- T c superconducting compound (Bi-2223) and the second, PnCs2, contains a giant magnetostrictive material (Terfenol-D). Magnetostriction is a property of ferromagnetic materials that causes them to change their shape/dimensions when subjected to external magnetic field. PnC studies that dealt with such materials are few. In this study, we focus on discussing the effects of the temperature and the magnetic field on the phononic gaps of these PnCs. For PnCs1, numerical results show that local resonant modes of elastic waves with brilliant sharpness can be realized. In addition, increasing the temperature leads to a decrease in the gap width which can be controlled by the magnetic field due to the effect of the magnetic field on the velocity of waves in the high- T c superconducting compound, the magnetic field effectively can widen the gap. For PnCs2, numerical results show that the gap width increases by increasing the magnetic field because the magnetostrictive material directly expanded in the presence of the magnetic field.

Effect of Oxygen Treatment on the Structural and Electrical Properties of Tl0.85Cd0.15Sr2CuO5−δ , Tl0.85Cd0.15Sr2Ca2Cu2 O 7−δ and Tl0.85Cd0.15Sr3Ca2Cu3 O 9−δ Superconductors

Abstract: The solid-state reaction was used to prepare three different high-temperature superconductors, namely Tl0.85Cd0.15Sr2CuO5−δ , Tl0.85Cd0.15Sr2Ca2Cu2 O 7−δ and Tl0.85Cd0.15Sr2Ca2Cu3 O 9−δ . The optimum calcinations were performed at 800∘C, and the sintering was performed within 855–860∘C. The samples were tested before and after oxygen treatment. It has been found that the oxygen flow on samples during preparation produces high-phase superconductors as compared with the samples prepared without oxygen flow. The four-probe techniques were used to measure the electrical resistivity to know the transition temperature (T c). It was found that the samples which were prepared with oxygen flow have the highest zero-transition temperatures (T c(offset)) of 85, 106 and 121 K for the samples Tl0.85Cd0.15Sr2CuO5−δ , Tl0.85Cd0.15Sr2Ca2Cu2 O 7−δ and Tl0.85Cd0.15Sr2Ca2Cu3 O 9−δ , respectively. X-ray diffraction spectrum showed all samples are polycrystalline with a tetragonal structure and also showed an increase of the c-axis and lattice constant with the increase of CuO layers and oxygen content. It was noticed that the change of CuO layers of all samples produced a modification in the transition temperature, mass density (ρ m) and c/a parameter.

Electronic and Electrical Conductivity of AB and AA-Stacked Bilayer Graphene with Tunable Layer Separation

Abstract: This humble work attempts to study the electronic and electrical conductivity characteristics of AB and AAstacked bilayer graphene (BLG) sheet, by using ab initio calculation. The electronic transport coefficient was calculated by using Boltzmann transport equations implanted in Boltztrap package at various temperatures from 80 to 380 K. First, this study will begin to experiment an interlayer spacing from 3.55 and 3.35 A respectively for AA and AB-BLG. If the distance between the layers is more than 5.00 A, the increase or decrease of energy does depend on the interlayer spacing so band gap is equal to zero. The electrical conductivity of AA and AB-BLG is compared to the experimental electrical conductivity of graphene monolayer under increasing spacing between layers to 4.00 A. Band gap decreases with the increasing space while conductivity increases with increasing space. AA-BLG electrical conductivity shows a value near to the experimental electrical conductivity of graphene ribbon for 4.00 A at 380 K. Nevertheless, the distance variation does not much affect the electronic and electrical characteristics of AB-BLG. In addition, the increase between the interlayer distances does not influence so much the electrical conductivity. Therefore, increasing the distance between interlayers decreases the electrical conductivity due to the increasing of band gap.

Theoretical Investigation of Cubic BaVO 3 and LaVO 3 Perovskites via Tran–Blaha-Modified Becke–Johnson Exchange Potential Approach

Abstract: The full potential linearized augmented plane wave method of density functional theory has been used to investigate the structural, electronic, magnetic and thermoelectric properties of cubic perovskites BaVO3 and LaVO3. The ferromagnetic ground state has been found to be stable by comparing the total energies of non-spin-polarized and spin-polarized calculations performed for optimized unit cells. For both compounds, the bond length and tolerance factor are also measured. From the band structures and density of states plots, it is found that both compounds are half-metallic. We found that the presence of V at the octahedral site of these perovskites develops exchange splitting through p-d hybridization, which results in a stable ferromagnetic state. The observed exchange splitting is further clarified from the magnetic moment, charge and spin of the anion and cations. Finally, we also presented the calculated thermoelectric properties of these materials, which show that half-metallic BaVO3 and LaVO3 materials are potential contenders for thermoelectric applications.