Superconducting Samples Research Articles

Investigation of BSCCO Superconductors with Ga Substitution by Solid State Method

Samples of (Bi2-xGax)Sr2CaCu2O2 superconductors with varying Ga substitution levels (x=0, 0.06, 0.12, 0.20) were synthesized using the solid-state reaction method. The effects of partial substitution of bismuth and gallium elements on the BSCCO structure were investigated in terms of their electrical, magnetic, structural, and mechanical properties. X-ray diffraction (XRD) was used to determine the crystalline phases, and samples A and B exhibited sharp peaks, indicating well-crystallized material with no Ga2O3 phase. SEM images were used to obtain microscopic views of all samples, and the elemental compositions of each element were determined from EDX spectra. The critical temperature was calculated from R-t measurements, and Sample A exhibited the highest Tc at 96K. Magnetic properties were investigated for all samples, including magnetic hysteresis behavior and magnetic moment. The critical current density (Jc) values were calculated using the Bean model by utilizing magnetic hysteresis.

Detection of Radiation Generated by Moving Josephson Vortices in a Bi<sub>2 +</sub> <sub><em>x</em></sub>Sr<sub>2 –</sub> <sub><em>x</em></sub>CuO<sub>6 + δ</sub> Single Crystal in High Magnetic Fields Directly in the Sample

A high-temperature superconductor sample with numerous internal Josephson junctions formed by atomic layers is a nonlinear system with unique dynamic properties. An external magnetic field penetrates in the sample in the form of moving Josephson vortices, which generate radiation. It has been shown that this radiation in a Bi2 +xSr2 –xCuO6 + δ(Bi2201) single crystal can be detected by means of a Josephson junction on a microbreak (break junction) directly inside the single crystal.

Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors.

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd2-xCexCuO4-δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm2. The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions.

Linear magnetic susceptibility of anisotropic superconductors of cuboidal shape

A simplified model of anisotropic magnetic susceptibility in the Meissner–London vortex-free state of cuboidal superconducting samples is presented. Using this model, precision measurements of the magnetic response in three perpendicular directions of a magnetic field with respect to primary crystal axes can be used to extract the components of the London penetration depth, thus enabling the evaluation of the general superfluid density tensor, which is needed in the analysis of the superconducting gap structure.

Inverse Faraday Effect in Superconductors with a Finite Gap in the Excitation Spectrum

The inverse Faraday effect (generation of a time-independent magnetic moment under the action of a circularly polarized electromagnetic wave) in mesoscopic superconducting samples with a finite gap in the excitation spectrum is analytically described. Within the modified time-dependent Ginzburg–Landau theory (Kramer–Watts-Tobin equations) for thin superconducting disks, it is shown that the temperature dependence of the optically induced magnetic moment is nonmonotonic in a wide range of parameters and contains a maximum. This maximum is due to the dephasing between the spatial oscillations of the magnitude and the phase of the order parameter, which arises with a decrease in the temperature and, correspondingly, in the characteristic relaxation time of perturbations in the superconducting condensate.

Inverse Faraday Effect in Superconductors with a Finite Gap in the Excitation Spectrum

The inverse Faraday effect (generation of a time-independent magnetic moment under the action of a circularly polarized electromagnetic wave) in mesoscopic superconducting samples with a finite gap in the excitation spectrum is analytically described. Within the modified time-dependent Ginzburg–Landau theory (Kramer–Watts-Tobin equations) for thin superconducting disks, it is shown that the temperature dependence of the optically induced magnetic moment is nonmonotonic in a wide range of parameters and contains a maximum. This maximum is due to the dephasing between the spatial oscillations of the magnitude and the phase of the order parameter, which arises with a decrease in the temperature and, correspondingly, in the characteristic relaxation time of perturbations in the superconducting condensate.

The effect of long-term exposure at room temperature on the thermal conductivity of the FeSe superconductor in the normal state

The temperature dependence of the thermal conductivity of the iron-based FeSe0.94 superconductor sample has been studied in the range of 4.2–200 K after long-term exposure for 7 years. The temperature dependence of thermal conductivity is predominantly phonon. This dependence was approximated taking into account phonon scattering by the boundaries of the sample, as well as scattering by dislocations, point defects, and phonon-phonon scattering. When comparing the parameters of this approximation with similar parameters for literature data for a freshly prepared polycrystalline sample, it turned out that long-term exposure led to a significant increase in all parameters. That is, long-term exposure causes a significant increase in the number of dislocations, and point defects and intensifies phonon-phonon scattering. For both samples, we found no effect of the structural phase transition at T ≈ 75 K from the tetragonal phase into the orthorhombic one on the thermal conductivity.

A Superconducting Micro-Magnetometer for Quantum Vortex in Superconducting Nanoflakes.

Superconducting quantum interferometer device (SQUID) plays a key role in understanding electromagnetic properties and emergent phenomena in quantum materials. The technological appeal of SQUID is that its detection accuracy for the electromagnetic signal can precisely reach the quantum level of a single magnetic flux. However, conventional SQUID techniques normally can only be applied to a bulky sample and do not have the capability to probe the magnetic properties of micro-scale samples with small magnetic signals. Herein, it is demonstrated that, based on a specially designed superconducting nano-hole array, the contactless detection of magnetic properties and quantized vortices in micro-sized superconducting nanoflakes is realized. An anomalous hysteresis loop and a suppression of Little-Parks oscillation are observed in the detected magnetoresistance signal, which originates from the disordered distribution of the pinned vortices in Bi2 Sr2 CaCu2 O8+δ . Therefore, the density of pinning centers of the quantized vortices on such micro-sized superconducting samples can be quantitatively evaluated, which is technically inaccessible for conventional SQUID detection. The superconducting micro-magnetometer provides a new approach to exploring mesoscopic electromagnetic phenomena of quantum materials.

Evolution of orbital excitations from insulating to superconducting MgTi2O4 films

Spinel oxides are well-known functional materials but rarely show superconductivity. Recently, emergent superconductivity was discovered in ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$, which is attributed to the increase of electron doping and the suppression of orbital order. Here, we utilized Ti $L$-edge resonant inelastic x-ray scattering to study the orbital excitations in superconducting (SC) and insulating ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ films. We find that the spectral weight of orbital excitations is enhanced and the energy of ${t}_{2g}$ intraband excitation is softened in the SC film compared to the insulating one, suggesting higher electron doping and a suppressed orbital order gap in the SC sample. These observations were further supported by our multiplet calculations using the minimal two-site model. Our results provide spectroscopic evidence for the competition between orbital order and superconductivity in ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ and shed light on searching for novel superconductors in spinel oxides.

Hybrid A-EHS Method for Fast Computation in Superconducting Bulks

In this article, a two-dimensional hybrid finite-element formulation is proposed to further reduce the computational time required for the time simulation of superconducting (SC) bulks. Low computational time formulations are important for the design stage of electrical machines with superconductors, where optimization tools are typically used. The proposed hybrid formulation is based on the partitioned <i>E</i>-<i>H</i> electromagnetic scheme (<i>EHS</i>) formulation and the magnetic vector potential formulation (<i>A</i>-formulation). The <i>EHS</i> formulation is used to solve the domains with highly nonlinear electric materials, while the <i>A</i>-formulation is used to solve the nonelectric domains. The main characteristics of the <i>EHS</i> are its partitioned formulation, where the matrix form of Amp&#x00E8;re&#x0027;s and Faraday&#x0027;s laws is separated and computed <i>a priori</i>, and the electric resistivity is defined at each node. The <i>EHS</i> formulation is first compared with the <i>H</i>-formulation for a single SC domain and then integrated with an <i>A</i>-formulation and compared with the <i>H</i> and <i>H</i>-<i>&phi;</i> formulations to simulate a bulk surrounded by air. Results verify the excellent accuracy of the <i>EHS</i> and <i>A-EHS</i> formulations, and a promising reduction of computational time is observed, with more emphasis on low levels of magnetization of the SC sample. When compared with the <i>H</i>-<i>&phi;</i> formulation, a time reduction between 48&#x0025; (6 T) and 90&#x0025; (1 T) is obtained.

Variasi Doping Pb Terhadap Pertumbuhan Fase Superkonduktor BPSCCO-2223 Pada Kadar Ca = 2,10 mol Menggunakan Metode Pencampuran Basah

Research has done about the Pb doping variation the growth of the superconductor phase BPSCCO-2223 at Ca 2,10 mol level using welt-mixing method. Samples were dissolved with HNO 3 and distilled with water slowly, then dried out at temperatures of 300, 400, and 600 o C gradually. The samples were calcined for 10 hours at 800 o C and sintered at 865 o C for 10 hours. The aimof this to determine the effect of Pb doping levels on the purity of superconducting phase. The XRD result showed that the addition of Pb doping levels affected the volume fraction value of BPSCCO-2223. The highest volume fraction was obtained at 0,4 mol Pb doping level of 70,31 % with an orientation degree value of 47,01 %. The lowest volume fractions was found in samples without Pb doping of 49,82 % with an orientation degree of 0 %. SEM result showed that the Pb doping addition caused the sample to be oriented in one direction and the empty space between slabs (voids). The meissner test result showed a magnetic rejection (weak meissner effect) by a BPSCCO-2223 superconductor sample at 0,4 mol Pb doping level.

Graphene doping effects on the magnetic and transport properties of YBa2Cu3O7-δ high temperature superconductor

In this work, bulk graphene-doped YBa2Cu3O7-δ (YBCO) high-temperature superconductor samples were prepared with composition of YBCO + x wt.% graphene nanoplatelets (G) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The X-ray diffraction patterns show the YBCO orthorhombic phase in all the samples. The SEM images show good grain connectivity between YBCO grains in graphene-doped samples. Furthermore, the broadening of resistivity under applied magnetic fields up to 9T and thermally activated flux creep in the mixed state were studied using Arrhenius plots. The activation energy U0 (H) increased with graphene doping results in better flux pinning and higher critical current densities. Moreover, improvement in the critical temperature (TC), upper critical field (μ0HC2) and the irreversibility field (μ0Hirr) were observed in graphene-doped samples as compared to the pure YBCO sample.

139La-NMR Study of Spin Dynamics Coupled with Hole Mobility in T*-type La0.86Eu0.86Sr0.28CuO4−δ

In T*-type cuprate oxides with five-oxygen coordination, the relationship between spin correlations and doped carriers has not been well understood. To clarify this relationship, and the magnetic and superconducting (SC) properties of T*-type cuprate oxides, we performed 139La-nuclear magnetic resonance (NMR) and electrical resistivity measurements on as-sintered (AS) and oxidation-annealed (OA) polycrystalline T*-type La0.86Eu0.86S0.28CuO4 (LESCO) to investigate its magnetic and SC properties. Upon cooling, the NMR spectrum of AS LESCO broadened below 3 K, where the nuclear spin–lattice relaxation rate 1/T1 with respect to the temperature exhibited a maximum, indicating the appearance of static magnetism. The temperature dependence of 1/T1 between 3 and 20 K was similar to that of resistivity, which displays semiconducting behavior. Furthermore, it was found that the energy scales of the transport gap and spin dynamics were comparable. These results suggest a close connection between the mobility of the doped carriers and low-energy spin dynamics, as reported for lightly doped T-type La2−xSrxCuO4. In the OA SC sample, we confirmed the absence of a magnetic order and the linear relation between 1/T1 and T above 10 K. These results suggest that the magnetic state coupled with holes markedly changes to the weakly correlated metallic state by oxidation annealing in the T*-type LESCO with x = 0.28.

Equivalent Models of Critical Current and Magnetization for Calculating the Magnetic Field in Simply Connected Structures Made of HTS Bulk and HTS Tape

This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies.

PARTIAL EFFECT OF (SRTİO3) NANO ON STRUCTURAL, ELECTRICAL, MAGNETIC CHARACTERISTICS OF SUPERCONDUCTORS COMPOUND YBA2CU3O7-Ó AT HIGH TEMPERATURE DEGREES

Three samples of (YBa2CU3O7-ó) were prepared for the research samples by using – solid interaction status method and annealing method under pressure of 8tan/CM2 ,at temperature 800oC via partial particles compensation of (SrTiO3) Nano in the rates (X=1.5X=1 X=0.5,) of the element Ba . The electrical inspections indicated large increase of critical temperature value Tc, upon compensation of the substance with value X=0.5 for Ba value, whereas critical temperature degree value reached 133k value, but decreased clearly upon compensation of substance X=1 for Ba value, whereas critical temperature degree value Tc reached 102.2K and when the substance compensated with value X=1.5 , improved critical temperature degree value to 122.2K Tc. The formation inspections of rays deviance indicated an obvious existence trapezium structure which existed in the three value in different variations of net distances A,B,C there was obvious increase in C distance . and upon inspections of Sample by FESEM instrument and in amplification rate of 100.00kx---500kx, it was found that granular size rate for the best sample was 33.38 in sample X=0.5 and the images of three samples indicated high accuracy and very detailed and shows makeup formation is bright which was related to light substances and dark areas related to heavy substances. The magnetic inspections indicated through Hystereris curve of the samples and the relationship between magnetic saturation MS and remained magnetic Mr and coerced force Hc and Represent Hystereris circles made-up in superconductors samples complete contrary relation between narrow of circles and improve of critical temperature degree Tc.

Residual Stress/Strain Analysis of Bulk YBCO Superconductors Using EBSD

Flux pinning of bulk YBa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> Cu <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> O <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{7-\delta }$</tex-math></inline-formula> (Y-123) superconductors is commonly done using secondary phase particles, mainly Y <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> BaCuO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_5$</tex-math></inline-formula> (Y-211) particles, which are created during the growth of the samples or additionally added. However, the crystallographic parameters of Y-211 particles indicate a misfit to the ones of Y-123, there will be residual strain around such particles within the Y-123 matrix. Here, we perform a dedicated analysis of electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD) data obtained on various Y-123 superconductor samples (Y-123 bulks prepared by melt-texture, melt-growth and the infiltration growth, YBCO foam struts and commercial YBCO coated conductors). This enables the strain distribution around such embedded secondary phase particles to be revealed down to the nanometer scale. The results are presented in the form of Kernel Average Misorientation (KAM) mappings. Around large Y-211 particles and around clusters, the strain can be so large that even subgrains in the Y-123 matrix are formed. The impact of the strain distribution on the flux pinning properties is discussed, as stress/strain can deliver an extra source of flux pinning. Therefore, it is essential to properly control the particle size as well as their distribution within the bulk sample to achieve the best superconducting performance.

Microstructural Parameters for Modelling of Superconducting Foams.

Superconducting YBaCuO (YBCO) foams were prepared using commercial open-cell, polyurethane foams as starting material to form ceramic YBaCuO foams which are then converted into superconducting YBCO by using the infiltration growth process. For modelling the superconducting and mechanical properties of the foam samples, a Kelvin-type cell may be employed as a first approach as reported in the literature for pure polyurethane foams. The results of a first modelling attempt in this direction are presented concerning an estimation of the possible trapped fields (TFs) and are compared to experimental results at 77 K. This simple modelling revealed already useful information concerning the best suited foam structure to realize large TF values, but it also became obvious that for various other parameters like magnetostriction, mechanical strength, percolative current flow and the details of the TF distribution, a refined model of a superconducting foam sample incorporating the real sample structure must be considered. Thus, a proper description of the specific microstructure of the superconducting YBCO foams is required. To obtain a set of reliable data, YBCO foam samples were investigated using optical microscopy, scanning electron microscopy and electron backscatter diffraction (EBSD). A variety of parameters including the size and shape of the cells and windows, the length and shape of the foam struts or ligaments and the respective intersection angles were determined to better describe the real foam structure. The investigation of the foam microstructures revealed not only the differences to the original polymer foams used as base material, but also provided further insights to the infiltration growth process via the large amount of internal surface in a foam sample.

Infield magnetic measurements of (Cu0.5Tl0.5)Ba2Ca3(Cu4−xTix)O12−δ (x = 0, 0.25, 0.50, 0.75) samples

We have synthesized (Cu0.5Tl0.5)Ba2Ca3(Cu4− xTi x)O12−δ ( x = 0, 0.25, 0.50, 0.75) superconductor samples at 880 °C and studied their superconducting features by XRD analysis, resistivity measurements, ac susceptibility measurements, FTIR absorption spectroscopy, and detailed infield magnetic measurements. By increasing x concentration of Ti doping, the a axis length of the tetragonal unit cell increases, whereas its c axis length decreases. Also, the Tc(onset), Tc( R = 0), and the magnitude of diamagnetism suppresses. The peak position of the apical oxygen modes stay unchanged, however the CuO2/TiO2 planar oxygen modes are softened with increasing x. The critical current density Jc of the samples suppress with an increased field. Suppression of Jc is more steep in doped samples. The doped atoms increase the population of confined defects, which act as pinning cores that increase energy per unit length of flux vortex ɛ. The pinning strength essentially depends on the ɛ; therefore, it also increases with x concentration of Ti doping. The superconductivity enhancement of doped samples is witnessed in increased coherence length ξ c, suppression of the Ginzburg-Landau parameter κ, and the penetration depth λD. The superior infield characteristics of doped samples indicated that Ti atoms act as efficient flux pinning centers whereas due to their presence in the final compound, the phase coherence of Cooper pairs in various unit cells is marginalized, which induces the suppression in Tc's and magnitude of diamagnetism in ac susceptibility measurements.

Моделирование особенностей магнитных свойств осесимметричных гранул жестких сверхпроводников II рода

Based on the equations of electrodynamics and the concept of a critical state for hard superconductors of the 2nd kind, numerical simulation of the magnetic properties of axisymmetric superconducting samples, in particular, granules, is performed for a number of models of the dependence of the critical current density on the magnetic field induction. The magnetic moment loops are calculated directly by integrating the integral equation for the current density over time. The phenomena of the peak effect and the asymmetry of the magnetization hysteresis loop are also considered using the indicated equation. Various versions of the functions used in the literature were used as peak functions. In addition to the hysteresis loop of the magnetic moment, the magnetic field induction at the center of axisymmetric samples, and the total penetration field, the profiles of the critical current density Jc(B) and the equilibrium magnetic moment for spherical granules were obtained. The method used for calculating the magnetic moment of superconductors makes it possible to take into account the equilibrium and nonequilibrium regions of the magnetization of the samples independently.

Simulation of the features of the magnetic properties of axisummetric granules of hard type II superconductors

Based on the equations of electrodynamics and the concept of a critical state for hard superconductors of the 2nd kind, numerical simulation of the magnetic properties of axisymmetric superconducting samples, in particular, granules, is performed for a number of models of the dependence of the critical current density on the magnetic field induction. The magnetic moment loops are calculated directly by integrating the integral equation for the current density over time. The phenomena of the peak effect and the asymmetry of the magnetization hysteresis loop are also considered using the indicated equation. Various versions of the functions used in the literature were used as peak functions. In addition to the hysteresis loop of the magnetic moment, the magnetic field induction at the center of axisymmetric samples, and the total penetration field, the profiles of the critical current density Jc(B) and the equilibrium magnetic moment for spherical granules were obtained. The method used for calculating the magnetic moment of superconductors makes it possible to take into account the equilibrium and nonequilibrium regions of the magnetization of the samples independently Keywords: magnetic moment, axisymmetric granules, type II superconductor, critical state, peak effect, equilibrium magnetic moment.