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Masato Murakami - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure and Flux Pinning of Reacted-and-Pressed, Polycrystalline Ba0.6K0.4Fe2As2 Powders.
    Materials (Basel Switzerland), 2019
    Co-Authors: Michael Rudolf Koblischka, Anjela Dimitrova Koblischka-veneva, Jörg Schmauch, Masato Murakami
    Abstract:

    The Flux Pinning properties of reacted-and-pressed Ba0.6K0.4Fe2As2 powder were measured using magnetic hysteresis loops in the temperature range 20 K ≤ T ≤ 35 K. The scaling analysis of the Flux Pinning forces ( F p = j c × B , with j c denoting the critical current density) following the Dew-Hughes model reveals a dominant Flux Pinning provided by normal-conducting point defects ( δ l -Pinning) with only small irreversibility fields, H irr , ranging between 0.5 T (35 K) and 16 T (20 K). Kramer plots demonstrate a linear behavior above an applied field of 0.6 T. The samples were further characterized by electron backscatter diffraction (EBSD) analysis to elucidate the origin of the Flux Pinning. We compare our data with results of Weiss et al. (bulks) and Yao et al. (tapes), revealing that the dominant Flux Pinning in the samples for applications is provided mainly by grain boundary Pinning, created by the densification procedures and the mechanical deformation applied.

  • optimization of matrix chemical ratio for high Flux Pinning in ternary nd eu gd ba2cu3oy
    Applied Physics Letters, 2001
    Co-Authors: M Muralidhar, M Jirsa, Naomichi Sakai, Masato Murakami
    Abstract:

    We prepared (Nd, Eu, Gd)Ba2Cu3Oy samples with various Nd: Eu: Gd ratios in the rare earth site. It was found that the three elements contributed to Flux Pinning in different ways. Nd mainly enhanced Flux Pinning at low magnetic fields, Eu controlled the second peak position and the irreversibility field, while Gd slightly enhanced intermediate and high-field Jc values. Scaling analyses for the Pinning force density as a function of the reduced field h=Ha/Hirr (where Hirr denote the irreversibility field) showed that the highest peak was achieved at h=0.56. This value is even higher than the theoretically predicted highest value of h=0.5. We also show that a maximum Flux Pinning can be achieved in the whole magnetic field when very fine secondary phase particles are dispersed in a superconducting (Nd, Eu, Gd)Ba2Cu3Oy matrix with an optimum Nd: Eu: Gd ratio.

  • Flux Pinning in ternary nd0 33eu0 33gd0 33 ba2cu3oy melt processed superconductors
    Applied Physics Letters, 1998
    Co-Authors: M R Koblischka, M Muralidhar, Masato Murakami
    Abstract:

    The Flux Pinning characteristics of ternary melt-processed (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) superconductors are studied in the temperature range 60⩽T⩽90 K. NEG samples exhibit a strongly developed peak effect in the dependence of the critical current densities on the external field, Ha. The scaling of the Pinning forces versus the reduced field h=Ha/Hirr (where Hirr denotes the irreversibility field) yields a peak at h0=0.5 which is an indication of Pinning provided by a spatial variation of the transition temperature. The presence of a weaker superconducting second phase is demonstrated by means of field cooling and warming experiments in fields up to 7 T. Furthermore, we discuss the possible effect of the magnetic moments of Gd and Nd on the Flux Pinning.

  • Flux Pinning and Applications of Melt Processed YBCO
    Superconductors Surfaces and Superlattices, 1994
    Co-Authors: Masato Murakami, N. Koshizuka, N. Sakai, D.n. Matthews, H. Takaichi, S. Tanaka
    Abstract:

    In this paper, I first summarize candidate Pinning centers in melt processed YBaCuO superconductors, along with the methods to introduce effective Pinning centers. Then I will introduce some applications of bulk oxide superconductors which exhibit a large Flux Pinning force.

  • Flux Pinning sites in melt-processed YBaCuO superconductors
    Phase Transitions, 1993
    Co-Authors: Masato Murakami, H. Fujimoto, K. Yamaguchi, N. Nakamura, N. Koshizuka, S. Tanaka
    Abstract:

    Abstract Melt processed YBaCuO superconductors exhibit high Jc values at 77 K and large magnetic fields. However, Flux Pinning sites which are responsible for such high Jc values are still unclear. Several candidates have been proposed as Flux Pinning sites, e.g., twin planes, oxygen defects, stacking faults, cracks, normal inclusions and dislocations. In this paper, we compare the effectiveness of these defects and find that Y2BaCuO5 inclusions and stacking faults are the most effective Pinning centers in well-annealed melt-grown YBaCuO.

Teruo Matsushita - One of the best experts on this subject based on the ideXlab platform.

  • Flux Pinning in Superconductors
    Springer Series in Solid-State Sciences, 2014
    Co-Authors: Teruo Matsushita
    Abstract:

    The book covers the Flux Pinning mechanisms and properties and the electromagnetic phenomena caused by the Flux Pinning common for metallic, high-Tc and MgB2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc., are introduced for the Pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the Flux Pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the Flux motion. The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism. The influence of the Flux Pinning on the vortex phase diagram in high Tc superconductors is discussed, and the dependencies of the irreversibility field are also described on other quantities such as anisotropy of superconductor, specimen size and electric field strength. Recent developments of critical current properties in various high-Tc superconductors and MgB2 are introduced. Other topics are: singularity in the case of transport current in a parallel magnetic field such as deviation from the Josephson relation, reversible Flux motion inside Pinning potentials which causes deviation from the critical state model prediction, the concept of the minimization of energy dissipation in the Flux Pinning phenomena which gives the basis for the critical state model, etc. Significant reduction in the AC loss in AC wires with very fine filaments originates from the reversible Flux motion which is dominant in the two-dimensional Pinning. The concept of minimum energy dissipation explains also the behavior of Flux bundle size which determines the irreversibility line under the Flux creep. The new edition has been thoroughly updated, with new sections on the progress in enhancing the critical current density in high temperature superconductors by introduction of artificial Pinning centers, the effect of packing density on the critical current density and irreversibility field in MgB2 and derivation of the force-balance equation from the minimization of the free energy including the Pinning energy

  • Critical current density and Flux Pinning in superconducting MgB2
    Physica C-superconductivity and Its Applications, 2008
    Co-Authors: Teruo Matsushita, Akiyasu Yamamoto, Jun-ichi Shimoyama, Masaru Kiuchi, K. Kishio
    Abstract:

    Abstract One of the most important factors which determine the critical current density in superconducting MgB 2 bulks and wires is the electrical connectivity and this can be improved by making the packing density of the superconductor high and by reducing the insulating oxide layers. In this study the Flux Pinning strength, which is another important factor, is investigated in detail. It is empirically known that the critical current density is proportional to the Flux Pinning force of grain boundaries and to the reciprocal size of MgB 2 grains. The Flux Pinning force of grain boundaries is estimated using the theoretical result of Yetter et al. for the electron scattering mechanism using the impurity parameter estimated from the residual resistivity of superconducting grains. The obtained result with the observed grain size approximately explains the experimental result and shows that the Flux Pinning by grain boundaries is dominant in MgB 2 . The potential for the high critical current density of MgB 2 is discussed by comparing with that of Nb 3 Sn.

  • Flux Pinning in Superconductors [3] -Flux Pinning Mecahnism-
    TEION KOGAKU (Journal of the Cryogenic Society of Japan), 2008
    Co-Authors: Teruo Matsushita
    Abstract:

    Flux Pinning interaction originates from the variation in the energy of a Flux line during its displacement across inhomogeneous regions called Pinning centers such as normal precipitates or grain boundaries. The Flux Pinning mechanism is classified according to the dominant energy involved in the interaction. Normal precipitates and grain boundaries work as strong Pinning centers through a condensation energy interaction. The field-induced Pinning resulting from a weak superconducting region is also classified in the condensation energy interaction. Magnetic interaction and kinetic interaction are also introduced. The Pinning mechanism of artificially introduced Nb into Nb-Ti is considered to be a kinetic energy interaction.

  • essential factors for the critical current density in superconducting mgb2 connectivity and Flux Pinning by grain boundaries
    Superconductor Science and Technology, 2008
    Co-Authors: Teruo Matsushita, M. Kiuchi, Akiyasu Yamamoto, J Shimoyama, Kohji Kishio
    Abstract:

    Electrical connectivity and Flux Pinning strength of grain boundaries are essential factors in determining the critical current density in superconducting polycrystalline MgB2. The effect of these factors is quantitatively investigated for a series of MgB2 bulk samples prepared by various methods. The electrical connectivity is evaluated using the percolation model and the obtained electrical connectivity is used for the estimation of the residual resistivity of superconducting MgB2 grains. The elementary Pinning force of grain boundaries is evaluated using the theoretical result of Yetter et al based on the electron scattering mechanism with the residual resistivity. It is found that the critical current density is approximately proportional to the product of the electrical connectivity, the elementary Pinning force of grain boundaries and the reciprocal grain size. This confirms that the critical current density is dominantly determined by the electrical connectivity and the Flux Pinning strength of grain boundaries. The Flux Pinning property in MgB2 under the condition of full electrical connectivity is compared with that in Nb3Sn. The obtained result shows that the Flux Pinning ability of pure MgB2 is comparable to or even higher than that of Nb3Sn, indicating a much higher potential in carbon-doped MgB2. This proves that the MgB2 is a promising superconductor for practical applications.

  • Flux Pinning in Superconductors
    2006
    Co-Authors: Teruo Matsushita
    Abstract:

    The Flux Pinning properties of RE-123 bulk superconductors, RE-123 coated conductors, Bi-2223 tapes and MgB2 superconductors are reviewed. In bulk superconductors, the Pinning mechanism of the lower Tc region, such as the Ba sites substituted by RE elements or twin boundaries with oxygen deficiency, is considered to be kinetic energy interaction under a proximity effect with the superconducting matrix. The dependence of the irreversibility field on the superconducting layer thickness is very complicated for RE-123 coated conductors. This is partly attributed to the thickness dependence of the critical current density that arises from the deterioration of the superconducting layer structure in thicker films and partly to the thickness dependence of the Flux creep. The reason for the dramatic improvement in the critical current properties is also discussed for Bi-2223 tapes fabricated using the over-pressure sintering technique. Theoretical analysis using the percolation theory clarifies that the low critical current density in conventional MgB2 in situ wires is attributed to low electrical connectivity, which is due to the voids and wetting insulating layers between grains. It is clarified that the Flux Pinning strength of the grain boundaries in MgB2 is significantly strong, and there is a room for a drastic increase in the Flux Pinning strength by dirtying the MgB2 through C-doping. Finally, the Flux Pinning mechanism of columnar defects nucleated by heavy ion irradiation is discussed. It is shown that the columnar defects larger than the coherence length are desirable to increase the probability of Flux lines being easily captured by the defects.

N. Koshizuka - One of the best experts on this subject based on the ideXlab platform.

  • Improved Flux Pinning in YxHo1-xBa2Cu3Oy fabricated by powder melting process
    Superconductor Science and Technology, 2001
    Co-Authors: Y. Feng, N. Koshizuka, A K Pradhan, Yong Zhao, L. Zhou
    Abstract:

    Flux Pinning and the peak effect of YxHo1-xBa2Cu3Oy melt-textured samples fabricated by a powder-melting-process method are investigated by a SQUID magnetometer in a magnetic field parallel to the c-axis of the samples. It has been found that the partial substitution of Ho for Y can lead to a strong enhancement of Flux Pinning over a wide temperature and field range in melt-textured YBa2Cu3Oy samples. A Jc value as high as 1.3×105 A cm-2 at 77 K and in self-field has been achieved in the Y0.4Ho0.6Ba2Cu3Oy sample. The enhancement of Flux Pinning may be attributed to the reduction of Y2BaCuO5 particles, the higher density of stacking faults and the paramagnetic moment of Ho3+. Contrary to the pure YBa2Cu3Oy sample, a peak effect can be observed below 77 K in H∥c in the Ho-added superconductors.

  • Flux Pinning and Applications of Melt Processed YBCO
    Superconductors Surfaces and Superlattices, 1994
    Co-Authors: Masato Murakami, N. Koshizuka, N. Sakai, D.n. Matthews, H. Takaichi, S. Tanaka
    Abstract:

    In this paper, I first summarize candidate Pinning centers in melt processed YBaCuO superconductors, along with the methods to introduce effective Pinning centers. Then I will introduce some applications of bulk oxide superconductors which exhibit a large Flux Pinning force.

  • Flux Pinning sites in melt-processed YBaCuO superconductors
    Phase Transitions, 1993
    Co-Authors: Masato Murakami, H. Fujimoto, K. Yamaguchi, N. Nakamura, N. Koshizuka, S. Tanaka
    Abstract:

    Abstract Melt processed YBaCuO superconductors exhibit high Jc values at 77 K and large magnetic fields. However, Flux Pinning sites which are responsible for such high Jc values are still unclear. Several candidates have been proposed as Flux Pinning sites, e.g., twin planes, oxygen defects, stacking faults, cracks, normal inclusions and dislocations. In this paper, we compare the effectiveness of these defects and find that Y2BaCuO5 inclusions and stacking faults are the most effective Pinning centers in well-annealed melt-grown YBaCuO.

  • Effect of Twin Planes on Flux Pinning in YBCO Prepared by MPMG Process
    Advances in Superconductivity V, 1993
    Co-Authors: H. Fujimoto, Masato Murakami, N. Nakamura, Takahiro Taguchi, N. Koshizuka
    Abstract:

    YBaCuO superconductors prepared by the melt-powder-melt-growth (MPMG) process have a high critical current density at 77 K and relatively high fields. It has been found that non-superconducting Y2BaCuO5 particles dispersed in the 123 superconducting matrix can work as strong Pinning centers, resulting in higher J C values. Despite 211 particles being the main Pinning centers, defects such as twin boundaries, oxygen deficiency and stacking faults are also considered to be able to work as Pinning centers in melt processed YBCO. In this study the effect of twin boundaries on the Flux Pinning was measured magnetically. The enhancement of J C was observed, when the magnetic field was applied parallel to the twin planes. The results indicate that twin planes contribute to Flux Pinning, but that their effect is not very large in MPMG processed samples.

Z.x. Shi - One of the best experts on this subject based on the ideXlab platform.

  • doping effect and Flux Pinning mechanism of nano sic additions in mgb2 strands
    Superconductor Science and Technology, 2011
    Co-Authors: Z.x. Shi, E.w. Collings, M A Susner, M D Sumption, X Peng, M Rindfleisch, M Tomsic
    Abstract:

    Superconducting MgB2 strands with nanometer-scale SiC additions have been investigated systematically using transport and magnetic measurements. A comparative study of MgB2 strands with different nano-SiC addition levels has shown C-doping-enhanced critical current density Jc through enhancements in the upper critical field, Hc2, and decreased anisotropy. The critical current density and Flux Pinning force density obtained from magnetic measurements were found to be substantially different from the values obtained through transport measurements, particularly with regards to magnetic field dependence. The differences in magnetic and transport results are largely attributed to connectivity related effects. On the other hand, based on the scaling behavior of the Flux Pinning force, there may be other effective Pinning centers in MgB2 strands in addition to grain boundary Pinning.

  • Peak Effect of Flux Pinning in Sc5Ir4Si10 Superconductors
    Journal of Applied Physics, 2010
    Co-Authors: Yue Sun, Z.x. Shi, M. Miura, Tsuyoshi Tamegai
    Abstract:

    Magnetic hysteresis loops (MHLs) have been comparatively measured on both textured and single crystalline Sc5Ir4Si10 superconductors. Critical current densities and Flux Pinning forces are calculated from MHLs by Bean model. Three kinds of peaks of the Flux Pinning force are found at low fields near zero, intermediated fields, and high fields near the upper critical field, respectively. The characters and origins of these peaks are studied in detail.

  • Flux Pinning in c-axis-oriented MgB2 thin film
    Physica C-superconductivity and Its Applications, 2007
    Co-Authors: Z.x. Shi, Y.x. Zhang, Eun-mi Choi, Sung-ik Lee
    Abstract:

    Abstract Flux Pinning behavior of c -axis-oriented MgB 2 thin film has been investigated by magnetization and transporting measurements. Critical current density J c and Flux Pinning force density F p were calculated from magnetization hysteresis loops. Pinning energy U 0 was estimated from both magnetization relaxation and resistivity transition curves. Based on the field and temperature dependence of critical current density, Flux Pinning force density and Pinning energy, Flux Pinning mechanism in MgB 2 superconductor has been analyzed and discussed in detail.

  • Effect of anisotropic superconductivity on Flux Pinning in polycrystalline MgB2
    Physica C: Superconductivity and its Applications, 2006
    Co-Authors: Z.x. Shi, J. Wang, Tsuyoshi Tamegai
    Abstract:

    Abstract Magnetization curves of dense polycrystalline MgB 2 have been measured by SQUID magnetometer and calculated by solving the Flux creep equation numerically. Considering the anisotropic superconductivity in MgB 2 and the grain orientation in polycrystalline samples as well as the Flux creep, the experimental data can be fitted very well by a two-exponential model. According to our fitting results, the nonscaling behavior of Flux Pinning force and the rapid decrease of critical current density of polycrystalline MgB 2 at medium and higher magnetic fields originate from the anisotropic superconductivity in MgB 2 , the dispersion of grain orientations and the Flux creep. Through this way, the real dependence of critical current density on temperature and magnetic field can be extracted, and the Flux Pinning mechanism is discussed. A universal method is therefore proposed for studying Flux Pinning in polycrystalline samples with intrinsic anisotropic superconductivity.

  • Flux-Pinning IN HIGH-T-C SUPERCONDUCTIVE FILMS
    Journal of Superconductivity, 1995
    Co-Authors: Z.x. Shi, X. Jin, X.x. Yao, X.s. Rong
    Abstract:

    Magnetization measurements have been performed onc-axis oriented Y- and Gd-based superconductive films in a wide range of the temperaturesT (4.2–85 K) and magnetic fieldsH (0–8 T) withH∥ c-axis. The influence of Flux creep on both the temperature dependence of critical current densityJ cm and the scaling behavior of Flux Pinning forceF p has been discussed in detail. The experimental results show that Y and Gd films have different Pinning mechanism. Flux Pinning-force peaks in high fields are observed in Gd film at high temperatures and can be considered as evidence for collective Pinning.

T Puig - One of the best experts on this subject based on the ideXlab platform.