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Showing papers in "Journal of Superconductivity and Novel Magnetism in 2013"


Journal ArticleDOI
TL;DR: In this paper, the authors reported synthesis and superconductivity at 3.7 K in REO0.5F 0.5BiS2 using vacuum encapsulation technique.
Abstract: We report synthesis and superconductivity at 3.7 K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having a ZrCuSiAs-type structure. The bulk polycrystalline compound is synthesized by the vacuum encapsulation technique at 780 ∘C in a single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in a tetragonal P4/nmm space group with lattice parameters a=4.015(5) A, c=13.362(4) A. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4 K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (Tc) onset at 3.7 K and Tc(ρ=0) at 3.1 K. The hump at Tc related to the superconducting transition is not observed in the heat capacity measurement and rather a Schottky-type anomaly is observed at below ∼6 K. The compound is slightly semiconducting in a normal state. Isothermal magnetization (MH) exhibited typical type II behavior with a lower critical field (Hc1) of around 8 Oe.

194 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the defects on magnetic properties of a bilayer Ising ferromagnetic antiferromagnetic model is studied by Monte Carlo simulations, for a nano-graphene lattice with spins that can take the values σ=3/2 and S=5/2.
Abstract: The effect of the defects on magnetic properties of a bilayer Ising ferromagnetic antiferromagnetic model is studied by Monte Carlo simulations, for a nano-graphene lattice with spins that can take the values σ=3/2 and S=5/2. We consider two ferromagnetic and antiferromagnetic bilayers with N=42 spins, with a random number of defects. We only consider the nearest-neighbor interactions between the site i and j on each layer. The effects of the defects on magnetization are investigated for fixed temperature, crystal field, and magnetic field values. The thermal dependency of each layer magnetization is calculated for fixed defect rate values K 3 and K 5, the crystal field, and external magnetic field. The magnetization hysteresis loops for several rate defects are also investigated as a function of the external magnetic field.

71 citations


Journal ArticleDOI
TL;DR: In this article, a soft chemical method using citric acid and tartaric acid routes followed by calcination at low temperature was used to obtain pure phase BiFeO3 nanoparticles.
Abstract: BiFeO3 nanoparticles were prepared via a soft chemical method using citric acid and tartaric acid routes followed by calcination at low temperature. Structural characterization showed remarkably different conditions for pure phase formation from both routes. The tartaric acid route was effective in obtaining pure phase BiFeO3 nanoparticles while citric acid route required leaching in dilute nitric acid to remove impurity phases. Further optical, magnetic, and dielectric characterizations of pure phase BiFeO3 nanoparticles obtained by tartaric acid route were done. X-ray diffraction and Raman spectroscopy confirmed the distorted rhombohedral structure of BiFeO3 nanoparticles. The average crystallite size of BiFeO3 nanoparticles was found to vary in the range 30–50 nm. Fourier Transformed Infrared spectra of BiFeO3 samples calcined at different temperatures were studied in order to analyze various bond formations in the samples. UV-Visible diffuse absorption showed that BFO nanoparticles strongly absorb visible light in the wavelength region of 400–580 nm with absorption cut-off wavelength of 571 nm. The band gap of BiFeO3 nanoparticles was found to be 2.17 eV as calculated from absorption coefficient spectra. Magnetic measurement showed saturated hysteresis loop indicating ferromagnetic behavior of BiFeO3 nanoparticles at room temperature. Temperature dependent dielectric constant showed anomaly well below the antiferromagnetic Neel temperature indicating decrease in antiferromagnetic Neel temperature of BiFeO3 nanoparticles.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the magnetocaloric properties of the Ce0.67Sr0.33MnO3 system near a phase transition from a ferromagnetic to a paramagnetic state are investigated.
Abstract: Magnetocaloric properties of the Ce0.67Sr0.33MnO3 system near a phase transition from a ferromagnetic to a paramagnetic state are investigated. The value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. The ΔSM distribution is uniform, which is desirable for an Ericson-cycle magnetic refrigerator. The data show that Ce0.67Sr0.33MnO3 can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas from the temperature of liquid natural gas to nearly the boiling point of hydrogen.

50 citations


Journal ArticleDOI
TL;DR: In this article, the magnetocaloric effect of the LSCM system was investigated for the Ericson-cycle magnetic refrigerator and it was shown that the magnetic entropy change distribution of the lSCM is much more uniform than that of gadolinium.
Abstract: Calculations of the magnetocaloric effect for La1−x Cd x MnO3 (LSCM) upon 0.05 T magnetic field variation have been carried out. It is found that magnetic entropy change distribution of the LSCM is much more uniform than that of gadolinium. This feature is desirable for an Ericson-cycle magnetic refrigerator. Furthermore, at different concentrations of Cd, the temperature range between 150 K and room temperature can be covered using the La1−x Cd x MnO3 system. Therefore, the LSCM system is beneficial for manipulating magnetocaloric refrigeration that occurs in various temperatures.

49 citations


Journal ArticleDOI
TL;DR: The flat band has an extremely singular density of states, and this property may give rise in particular to surface superconductivity, which in principle could exist even at room temperature as mentioned in this paper.
Abstract: Topological media are systems whose properties are protected by topology, and thus are robust to deformations of the system. In topological insulators and superconductors, the bulk-surface and bulk-vortex correspondence gives rise to the gapless Weyl, Dirac, or Majorana fermions on the surface of the system and inside vortex cores. In gapless topological media, the bulk-surface and bulk-vortex correspondence produce topologically protected gapless fermions without dispersion—the flat band. Fermion zero modes forming the flat band are localized on the surface of topological media with protected nodal lines and in the vortex core in systems with topologically protected Fermi points (Weyl points). Flat band has an extremely singular density of states, and this property may give rise in particular to surface superconductivity, which in principle could exist even at room temperature.

48 citations


Journal ArticleDOI
TL;DR: In this article, the differences between the measured and calculated electronic band structures look insignificant, but can be crucial for understanding of the mechanism of high temperature superconductivity in iron-based superconductors.
Abstract: ARPES experiments on iron based superconductors show that the differences between the measured and calculated electronic band structures look insignificant, but can be crucial for understanding of the mechanism of high temperature superconductivity. Here, we focus on those differences for 111 and 122 compounds and discuss the observed correlation of the experimental band structure with the superconductivity.

46 citations


Journal ArticleDOI
TL;DR: In this article, a review of interesting new problems concerning high critical temperature superconductors (HTS) Josephson junction (JE) of inspiration also for other systems is presented.
Abstract: Coherent passage of Cooper pairs in a Josephson junction (JJ) above the liquid nitrogen temperature has been the first impressive revolutionary effect induced by high critical temperature superconductors (HTS) in the domain of the study of Josephson effect (JE). But this has been only the start. A d-wave order parameter has lead to significant novel insights in the physics of the JE turning into a device the notion of a π-junction. Spontaneous currents in a frustrated geometry, Andreev bound states, long-range proximity effect have rapidly become standard terms in the study of the JE, standing as a reference bench for conventional systems based on low critical temperature superconductors (LTS) and inspiring analogies for junctions based on novel superconductors discovered in the meantime. The extreme richness of the physics of HTS JJs has not been adequately supported by the expected impact in the applications, the main reason lying in the complexity of these materials and in the consequent unsatisfactory yield and reproducibility of the performances of the JJs within the required limits. The continuous progress in material science, and specifically in the realization of oxide multi-layers, and in nanotechnologies applied to superconductors, accompanied by the advances in a better understanding of the properties of HTS and of HTS devices, has as a matter of fact opened possible novel scenarios and interest in the field. We intend to give a brief overview on interesting new problems concerning HTS JJs of inspiration also for other systems. We also review some ideas and experimental techniques on macroscopic quantum decay phenomena occurring in Josephson structures. The attention is mainly addressed to intermediate levels of dissipation, which characterize a large majority of low critical current Josephson devices and are therefore an unavoidable consequence of nanotechnology applied more and more to Josephson devices.

45 citations


Journal ArticleDOI
TL;DR: In this paper, the transmittance of two types of one-dimensional periodic structures, namely, alternating layers of a dielectric material and a superconductor, was compared.
Abstract: We present the transmittance of two types of one-dimensional periodic structures. The first type of structure consists of alternating layers of a dielectric material. The second type of structure consists of alternating layers of a dielectric material and a superconductor whose dielectric properties are described by the two-fluid model. The variance of the intensity and the bandwidth of the transmittance are strongly dependent on the thicknesses, temperature, and frequencies. We have compared the transmittance spectra and present some details about the two types of structure. In the first type, we will make a comparison between the optical properties of the high temperature superconducting photonic crystal (HTScPC) by using the YBa2Cu3O7 as a superconductor layer with SrTiO3 as a dielectric layer. The second type consists of the dielectric photonic crystals (DPCs) and Al2O3 or MgO with SrTiO3 within the ultra-violet region. The comparison obtained according to the difference of the thickness of SrTiO3 and the variance of the number of periods. The common result is changed in the number of PBGs within the UV range.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the structural, electronic, and magnetic properties of dilated magnetic semiconductors (DMS) were investigated using the full-potential linearized augmented plane waves (FP-LAPW) method within the density functional theory and local spin-density approximation.
Abstract: We investigate the structural, electronic, and magnetic properties of (M = Fe, Mn)-based zinc blende diluted magnetic semiconductors (DMS) (Al, Ga, In)1−x M x N for (x=0.0625,0.125,0.25), using first-principles calculations with the full-potential linearized augmented plane waves (FP-LAPW) method within the density functional theory and local spin-density approximation. The analysis of electronic structures and magnetic properties show that (Al, Ga, In)1−x Fe x N at (x=0.0625,0.125,0.25) are magnetic insulators, and In1−x Mn x N at (x=0.0625,0.125) are metallic in nature. On the other hand the (Al, Ga)1−x Mn x N at (x=0.0625,0.125,0.25) and In0.75Mn0.25N are half-metallic ferromagnets with magnetic spin polarization of 100 %, where the ferromagnetic ground states result from a double-exchange mechanism, and these compounds are predicted to be good candidates for spintronic applications.

42 citations


Journal ArticleDOI
TL;DR: In this article, a phenomenological model is used to calculate magneto-caloric properties of Ge0.95Mn0.05 films fabricated with substrate temperatures of 85, 100, and 120 ǫC.
Abstract: In this paper, a phenomenological model is used to calculate magneto-caloric properties of Ge0.95Mn0.05 films fabricated with substrate temperatures of 85, 100, and 120 ∘C. Calculations showed that the ferromagnetic Mn5Ge3 phase improves magneto-caloric properties of the Ge0.95Mn0.05 films. It is suggested that Ge0.95Mn0.05 films are suitable candidates as refrigerants near room-temperature region.

Journal ArticleDOI
TL;DR: In this article, a modification is suggested for a hysteresis model to become completely adequate for nanocrystalline CoFe2O4 hystresis, and a verification of the modified model is carried out, showing good agreement between simulation and experimental measurements of calcined at different temperatures or pressed at different pressures.
Abstract: In this article, a modification is suggested for a hysteresis model to become completely adequate for nanocrystalline CoFe2O4 hysteresis. A verification of the modified model was carried out, showing good agreement between simulation and experimental measurements of nanocrystalline CoFe2O4 calcined at different temperatures or pressed at different pressures. A prediction of the hysteresis loss of nanocrystalline CoFe2O4 was formulated and estimated as a result of the modified model.

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties such as saturation magnetization (Ms), remanence (Mr), squareness ratio (Mr/Ms), and coercivity (Hc) are calculated from the M-H-loops.
Abstract: Nanostructured M-type hexaferrite Ba1−xCaxFe11.5Cr0.5O19 (x=0.0–0.5) powders have been synthesized by means of the sol-gel autocombustion method. The materials are characterized by differential scanning calorimetry, thermogravimetry, Fourier transform infra-red spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometry. X-ray diffraction analysis confirms the formation of M-type hexagonal phase and few traces of α-Fe2O3 are also observed. The c/a ratio falls in the expected range from a value of 3.97 to 3.94 of M-type hexaferrites. The average crystallite size is found to be in the range 15 to 36 nm, which is good enough to obtain the suitable signal-to-noise ratio in the high-density recording media. DC electrical resistivity at room temperature enhances up to 11.2×109 Ω cm (x=0.4) and then drops upon increasing the Ca2+ contents further. The magnetic properties such as saturation magnetization (Ms), remanence (Mr), squareness ratio (Mr/Ms) and coercivity (Hc) are calculated from the M–H-loops. The maximum magnetization and remanence reduces from a value of 52 to 33 and 33 to 16 emu/g, respectively, which attributes to the decrease of magnetic moment, and hence reduction in the superexchange interaction. The coercivity enhances from 4378 to 4706 Oe, which attributes to the increase in magnetocrystalline anisotropy due to the reduction of particle size. Owing to these properties, the synthesized nanomaterials can be considered useful for high-density recording media and permanent magnets.

Journal ArticleDOI
TL;DR: The structural, optical, and magnetic properties of multiferroic GdMnO3 nanoparticles synthesized by the modified sol-gel route have been investigated in this article.
Abstract: The structural, optical, and magnetic properties of multiferroic GdMnO3 nanoparticles synthesized by the modified sol–gel route have been investigated. Raman spectroscopy and X-ray diffraction along with Rietveld refinement confirm the pure phase of the GdMnO3 nanoparticles having an orthorhombic perovskite (space group: Pnma) type structure. The morphology was examined by scanning electron microscopy. Energy dispersive spectroscopy confirms the stoichiometry of the composition. The room temperature UV-visible absorption spectrum using Tauc’s relation gives an optical band gap of ∼2.9 eV. A magnetization study of the GdMnO3 nanoparticles was performed over a temperature range of 2–300 K at an applied field of 0.05 T by using a vibrating sample magnetometer. An effective magnetic moment (μ eff) of ∼9.2μ B was obtained. The system is paramagnetic at room temperature and shows a ferromagnetic-like nature at 2 K as the applied magnetic field aligns the Gd moments and the contribution of the net moment of Gd spins is larger than that of the anti-ferromagnetically canted state of the Mn spins.

Journal ArticleDOI
TL;DR: In this paper, the influence of magnetic field on the resistivity of the magneto-active elastomer has been studied and a significant dependency of the ability to conduct electric current was found on mechanical influence (piezoresistive effect) and combined influence of mechanical force and magnetic field.
Abstract: A study of the influence of magnetic field on the resistivity of the magnetoactive (magnetorheological) elastomer has been conducted. The material consisted of a soft polymer matrix and magnetic fillers being powders of Fe, Ni, and the Fe–Nd–B alloy. Under the influence of the field with a value of 300 mT, the elastomer exhibited the magnetoresistive effect: The specific electric resistivity of the material was noticed to decrease by 3 orders. In addition, a significant dependency of the ability to conduct electric current was found on mechanical influence (piezoresistive effect) and combined influence of mechanical force and magnetic field. In the case considered, the behavior of the electroconductivity has a complex character.

Journal ArticleDOI
TL;DR: In this paper, a laser line scanning method was applied to process rectangular cross-section Bi-2212 monoliths containing 2.9 % Ag using a CO2 laser.
Abstract: A novel Laser Line Scanning method has been applied to process rectangular cross-section Bi-2212 monoliths containing 2.9 % Ag using a CO2 Laser. Although previous work has suggested the use of nIR lasers (≈0.8–1.1 μm) for melt-processing metal oxide superconductors, the results obtained here demonstrate that mid-IR radiation from a CO2 laser (10.6 μm) may be just as convenient for such a purpose while it enables processing large surface areas. The samples described here were processed at traverse rates ranging between 15 and 60 mm/h, exhibited a complex textured microstructure and yielded highest Ic values of 71 A at 77 K.

Journal ArticleDOI
TL;DR: In this paper, a spinel phase CoFe2O4 was synthesized using Cetyl Trimethyl Ammonium Bromide (CTAB) as a surfactant at temperature 160°C.
Abstract: This paper presents a low temperature (130 and 160 °C) synthesis route to prepare the spinel phase CoFe2O4 nanoparticles and nanorods. A one-dimensional (1-D) structure of Co-ferrite was successfully synthesized using Cetyl Trimethyl Ammonium Bromide (CTAB) as a surfactant at temperature 160 °C. Structural, electrical, and magnetic measurements have been performed using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and the Vibrating Sample Magnetometer (VSM). XRD patterns show a pure spinel (fcc) structure, showing a complete phase formation at a low temperature of 160 °C, without any subsequent sintering. Average crystallite sizes have been calculated by Sherrer’s and Williamson-Hall methods. As prepared CoFe2O4 nanorods exhibited a uniform shape of diameter 60–80 nm and 600–900 nm in length. The FTIR spectrum for Co-ferrite nanorods shows two intrinsic lattice absorption bands for tetrahedral and octahedral sublattices. DC electrical resistivity of CoFe2O4 nanorods is high up to ∼108 (Ω-cm), as compared to CoFe2O4 nanoparticles (∼107 Ω-cm) at 373 K. Dielectric parameters were measured using a LCR meter, in the frequency range of 1 kHz to 5 MHz. The real and imaginary part of the dielectric constant (e′ and e″) and dielectric loss tangent (tanδ) reduces for CoFe2O4 nanorods in comparison to nanoparticles, and has a value of 13.6 and 0.0416, respectively. Magnetic properties were characterized by VSM under a field of 10 kOe and showed that the 1-D structure reduces the magnetization of nanocrystalline CoFe2O4 from 65 emu/gm to 54 emu/gm.

Journal ArticleDOI
TL;DR: In this article, the effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr0.45Er0.4MnO3 powder samples have been studied.
Abstract: The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr0.45Er0.15Sr0.4MnO3 sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.

Journal ArticleDOI
TL;DR: In this article, Heusler-type Ni-Mn-Ga glass-coated microwires with total diameters, D, from 16 until 65μm consisted of a metallic nucleus with diameters between 10 and 31μm and surrounded by the glass coating by the Taylor-Ulitovsky technique and measured the magnetocaloric effect, MCE, by the recently introduced precise method allowing the detection of a change in the temperature, ΔT, with an accuracy of below 10−3 K.
Abstract: We prepared Heusler-type Ni–Mn–Ga glass-coated microwires with total diameters, D, from 16 until 65 μm consisted of a metallic nucleus with diameters, d, between 10 and 31 μm and surrounded by the glass coating by the Taylor–Ulitovsky technique and measured the magnetocaloric effect, MCE, by the recently introduced precise method allowing the detection of a change in the temperature, ΔT, with an accuracy of below 10−3 K. As-prepared microwires did not show ferromagnetic ordering at least near room temperature. Annealing above 773 K even for few minutes results in drastic change of magnetic properties: annealed sample show magnetization versus temperature dependence typical for ferromagnetic behavior with the Curie temperature about 315 K. Analysis of the X-ray diffraction allows us to identify presence of cubic phase in as-prepared state with the space group Fm3m and some amount of the tetragonal phase with space group I4/mmm. We measured directly the MCE, ΔT, in annealed samples. Before glass removal, we observed ΔT≈0.06 K for sample 1 and 0.08 K for sample 2. After glass removal of sample 1, ΔT increased until 0.22 K. Observed MCE is associated with magnetic (paramagnetic–ferromagnetic) and probably structural (austenite–martensite) phase transitions. Temperatures of the peak values of MCE were found to be of ∼318 K and ∼309 K, respectively Use of the glass-coating fabrication technique allows fabrication of composite thin wires from the brittle Ni–Mn–Ga alloy that cannot be cold-drawn to create fibers by conventional methods.

Journal ArticleDOI
TL;DR: In this paper, the physical and magnetic properties of textured materials prepared by a LFZ melting technique and annealed for different times (60, 72, 96 and 120 hours) were reported.
Abstract: In this study, we report the physical and magnetic properties of Bi2Sr2CaCu2O x textured materials prepared by a LFZ melting technique and annealed for different times (60, 72, 96 and 120 h) SEM images of the annealed samples for 96 and 120 hours indicate very good alignment with the longitudinal rod axis In all cases, X-ray diffraction patterns show that the Bi-2212 phase is the major one The magnetization measurements have been carried out as a function of the magnetic field up to 9 kOe J c values of the samples were calculated by using the Bean model The results indicate that the different annealing time has no significant effects on the T c values but, significant change on the critical current values of samples, J c, has been obtained for sample annealed at 96 hours We also found that the maximum critical density of J c is 55×105 A/cm2 at 10 K for the 96 hours annealed sample

Journal ArticleDOI
TL;DR: In this article, the structural and magnetic properties of the Ln2MnCoO6 (Ln=La and Dy) produced by the combustion method are reported, and the samples were characterized by X-ray diffraction with Rietveld refinement, and their magnetic properties by studying the dependence of the magnetization with the magnetic field and temperature.
Abstract: In this article, the structural and magnetic properties of the Ln2MnCoO6 (Ln=La and Dy) produced by the combustion method are reported. The samples were characterized by X-ray diffraction (XRD) with Rietveld refinement, and their magnetic properties by studying the dependence of the magnetization with the magnetic field and temperature. XRD analysis reveals that the La2MnCoO6 (LCM) consists of a mixture of crystalline orthorhombic, monoclinic, and rhombohedral phases. This mixture might be originated by the mixing of valence states of the Co+2/Mn+4 and Co+3/Mn+3. Dy2CoMnO6 (DCM) presents a mixed composition of hexagonal and orthorhombic structures with the transition metal atoms in mixed valences. Magnetic measurements show that the magnetic transition temperature T C decreases from 150 K to 85 K when the La ions are replaced by Dy. We also observe that the magnetic order changes from a ferromagnetic to a ferrimagnetic when La is replaced by Dy.

Journal ArticleDOI
TL;DR: In this paper, the effect of various concentrations of polyvinylpyrolidone (PVP) on the resultant CoFe2O4 powder was studied and the resultant samples were characterized by XRD, TG/DSC, HR-SEM and VSM.
Abstract: CoFe2O4 particles were synthesized using metallic nitrates and polyvinylpyrolidone (PVP) using sol–gel method followed by calcination for 2 h at 960 °C. PVP performed as a surfactant and the effect of various concentrations of PVP on the resultant CoFe2O4 powder was studied. The resultant samples were characterized by XRD, TG/DSC, HR-SEM and VSM. X-ray diffraction results indicated the crystalline phase of CoFe2O4 particles and impurity phase of hematite was observed for higher PVP concentrations. SEM images demonstrated the influence of PVP concentration on the size of the particles. By VSM measurements, the variations in magnetic properties with respect to PVP concentration are studied. All the magnetic characteristics H c , M s and M r increased for 6 wt% and 15 wt% of PVP concentration. The CoFe2O4 particles synthesized with the optimum concentration of PVP may be very attractive for potential applications because of their outstanding magnetic properties (M s =81.1 Am2/kg, H c =831 Gauss).

Journal ArticleDOI
TL;DR: In this article, the spin response is uniquely determined by the pairing symmetry, and possible spin resonance excitations may occur at an incommensurate momentum about (0.7π, 0.5π) for the d-wave symmetry, while the transverse spin excitation near (0,0) is enhanced for the p-wave and no spin resonance signature is seen for the s-wave pairing symmetry.
Abstract: Starting from a two-orbital model and based on the random phase approximation, spin excitations in the superconducting state of the newly discovered BiS2 superconductors with three possible pairing symmetries are studied theoretically. It is found that the spin response is uniquely determined by the pairing symmetry. Possible spin resonance excitations may occur at an incommensurate momentum about (0.7π,0.7π) for the d-wave symmetry, while the transverse spin excitation near (0,0) is enhanced for the p-wave symmetry and no spin resonance signature is seen for the s-wave pairing symmetry. These distinct features may be used for probing or determining the pairing symmetry in this newly discovered compound.

Journal ArticleDOI
TL;DR: In this article, the doped ZnO system Zn0.94Co0.05Cu0.01O (ZCCO) was prepared as a nano-polycrystalline by a sol-gel process, then air annealed at different tempera- tures.
Abstract: The doped ZnO system Zn0.94Co0.05Cu0.01O (ZCCO) was prepared as a nano-polycrystalline by a sim- ple sol-gel process, then air annealed at different tempera- tures. Applying X-ray diffraction (XRD) and the Rietveld method, structural analysis showed that Co and Cu replace Zn substitutionally yielding ZCCO single phase. The re- fined u-fractional coordinate of Zn increases monotonically by an annealing temperature from 0.3546 at 500 °C reach- ing 0.3722 at 800 °C, very near from the ideal value 0.375. The Zn tetrahedrons become more symmetric and the dis- tortion is gradually relieved by annealing up to 800 °C. An- nealing at 900 °C introduces tetrahedron distortion in an opposite way. The zero field cooled (ZFC) and field cooled (FC) magnetization versus the temperature at different ap- plied fields and the magnetization versus the applied field at different temperatures were carried out. The system ex- hibits a ferromagnetic behavior at room temperature. As the annealing temperature increases from 550 to 900 °C, the saturation magnetization at 300 K increases from 0.0507 to 0.1088 emu/g.

Journal ArticleDOI
TL;DR: In this paper, the effect of silver addition on superconducting performance of bulk YBCO (YBa2Cu3O7) superconductor was investigated using X-ray diffraction data.
Abstract: We report the effect of silver addition on superconducting performance of bulk YBCO (YBa2Cu3O7) superconductor. All the studied samples are prepared by conventional solid-state reaction method. Rietveld fitted X-ray diffraction data confirmed the single phase formation for all the studied samples. Detailed AC susceptibility measurements as a function of driven AC amplitude (1 Oe–17 Oe) of these samples revealed the enhancement of grains coupling with increasing Ag content in YBCO + Ag x composite system. 10 wt% Ag added YBCO superconductors exhibited the optimal intergranular coupling. The Scanning Electron Microscopy (SEM) observations indicate an increase in the grains connectivity in terms of narrow grain boundaries for doped samples. The average grain size is found to increase with Ag doping. It is concluded that limited addition of Ag in bulk YBCO superconductor significantly improves the grains coupling and, as a result, the optimal superconducting performance. YBCO + Ag composites could prove to be potential candidates for bulk superconducting applications of the studied high-T c system.

Journal ArticleDOI
TL;DR: In this paper, structural and micro-structural analyses were carried out applying X-ray diffraction (XRD) and Rietveld method, which showed that Mg2+ and Al3+ replace Zn2+ substitutionally yielding ZMAO single phase.
Abstract: The doped ZnO systems Zn1−x−y Mg x Al y O (ZMAO) (x=0, 0.05, 0.1 and y=0, 0.05 and 0.1) were prepared as polycrystalline nanoparticle by a simple sol–gel process. Structural and microstructural analyses were carried out applying X-ray diffraction (XRD) and Rietveld method. Analysis showed that Mg2+ and Al3+ replace Zn2+ substitutionally yielding ZMAO single phase. Replacing Zn+2 affects the lattice parameters in opposite ways, the parameter c decreases while a increases with an overall decrease in the ratio c/a, which deviates the ZMAO lattice gradually from the wurtzite hexagonal structure. The magnetization versus temperature was measured with zero-field cooled (ZFC) and field cooled (FC) at different applied fields. Also, measurement of magnetization versus applied field was carried out at different temperatures. The system exhibits ferromagnetic properties at room temperature. The saturation magnetization increases as Al doped amount increases.

Journal ArticleDOI
TL;DR: In this paper, a single-step solid-state reaction technique was used to obtain superconducting samples of type (nano-Ag)xCu0.5Tl 0.5Ba2Ca2Cu3O10−δ.
Abstract: Superconducting samples of type (nano-Ag)xCu0.5Tl0.5Ba2Ca2Cu3O10−δ, x=0.0, 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%, were prepared under ambient pressure via a single step solid-state reaction technique at 850 °C. The prepared samples were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and differential scanning calorimetry (DSC). The electrical properties of the prepared samples were investigated using the electrical resistivity and I–V measurements. The low addition of nano-Ag up to x=1.5 wt.% enhanced the phase formation and improved the superconducting transition temperature Tc, critical current density Jc, and melting temperature. For x>1.5 wt.%, a reverse trend was observed.

Journal ArticleDOI
TL;DR: In this article, the effect of a 100mA current intensities in two configurations was studied: (i) direct current (connecting the seed rod to the positive pole and the feed to the negative one) and (ii) reverse current (positive pole connected to the feed rod and negative to the seed one).
Abstract: Bi-2212/Ag superconducting ceramics were grown using the electrically assisted laser floating zone (EALFZ) technique. The main goal was improving the superconducting properties by applying an electrical current through the sample during the solidification process. The effect of a 100 mA current intensities in two configurations were studied: (i) direct current (connecting the seed rod to the positive pole and the feed to the negative one) and (ii) reverse current (positive pole connected to the feed rod and negative to the seed one). The resulting textured cylindrical bars were annealed in order to obtain the superconducting phases. A strong correlation between current polarity, grain alignment and superconducting properties was observed. The rods grown under direct current exhibit higher critical current density (∼3000 A/cm2) than the ones grown under conventional method (∼2300 A/cm2) or under reverse current condition (∼35 A/cm2). The superior value obtained for the direct current results from a better grain alignment and fewer amount of second phases.

Journal ArticleDOI
TL;DR: In this article, the effect of rare-earth Eu3+ ions substitution at Fe3+ site on the structural and magnetic properties of M-type hexaferrites was investigated especially using sol-gel auto-combustion technique.
Abstract: Nano-structured M-type hexaferrites having the nominal composition Sr0.8Ca0.2Eu x Fe12−x O19 (x=0.0, 0.05, 0.1, 0.15, 0.2, 0.25) have been synthesized by a sol-gel auto-combustion technique. The aim of the present study is to investigate the effect of rare-earth Eu3+ ions substitution at Fe3+ site on the structural and magnetic properties of M-type hexaferrites that might have not been previously explored especially using the sol-gel auto-combustion technique. The samples have been characterized by Differential Scanning Calorimetry (DSC), Fourier Transform Infra-Red (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (ED-XRF) and vibrating sample magnetometer (VSM). The XRD analysis confirms the formation of single M-type hexaferrite phase. The ratio ‘c/a’ lies in the expected range of 3.946–3.951 for M-type hexaferrites phase. The crystallite size was found to be in the range of 15–45 nm, which is sufficient to obtain the suitable signal to noise ratio in the high density recording media. Scanning Electron Microscopy (SEM) analysis exhibits the morphology of grains to be hexagonal platelet. The values of remanence (M r ) and maximum magnetization (M) lie in the range 31–68 emu/g and 47–90 emu/g, respectively. The coercivity (H c ) values lie in the range of 2412–4046 Oe and enhancement in the coercivity may be due to increase in the shape anisotropy. The magnetic properties such as coercivity (H c ), magnetization (M), and retentivity (M r ) make the synthesized materials useful for applications in the recording media.

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TL;DR: In this paper, the volume pinning force increases with increasing synthesis or sintering pressure (0.1 MPa-2 GPa), while it stays practically unchanged in those prepared at low temperature (800-°C).
Abstract: The volume pinning force, F p(max), increases with increasing synthesis or sintering pressure (0.1 MPa–2 GPa) in materials prepared at high temperature (1050 °C) while it stays practically unchanged in those prepared at low temperature (800 °C). The position of F p(max) can be shifted to higher magnetic fields by: (1) increasing the manufacturing pressure or decreasing the temperature (2) additions (Ti, SiC, or C, for example), and (3) in-situ preparation. Grain boundary pinning (GBP) dominates in materials prepared at low temperatures (600–800 °C), while high-temperature preparation induces strong point pinning (PP) or mixed pinning (MP) leading to outstanding properties. In materials produced by spark plasma sintering (SPS), the position of F p(max) is higher than expected for both grain boundary and point pinning. The distribution of boron and oxygen in MgB2 based material, which can changed by additions or the preparation conditions, significantly affects the type and strength of pining. Materials prepared under a pressure of 2 GPa with a nominal composition of Mg:7B or Mg:12B consist of 88.5 wt % MgB12, 2.5 wt % MgB2, 9 wt % MgO or 53 wt % MgB12, 31 wt % MgB20 16 wt % MgO, respectively. Their magnetic shielding fractions at low temperatures are 10 % and 1.5 %, with a transition temperature, T c of 37.4–37.6 K. Although their magnetic critical current density at zero field and 20 K was 2–5×102 A/cm2, they were found to be insulating on the macroscopic level.