Yazar "Gokhfeld, D. M." seçeneğine göre listele

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    Hysteresis loops of MgB2 + Co composite tapes
    (Springer, 2013) Altin, E.; Gokhfeld, D. M.; Komogortsev, S. V.; Altin, S.; Yakinci, M. E.
    The (MgB2)(1-x) Co (x) composite tapes fabricated by the ex situ PIT method were investigated. The structural and magnetic properties were characterized. Only MgB2 and Co phases were observed in the composites while x a parts per thousand currency sign 0.2. A superconducting transition temperature was stable for these samples. Enhancement of the critical current density is found for x = 0.1.
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    Jc enhancement and flux pinning of Se substituted YBCO compound
    (Springer, 2013) Yakinci, Z. D.; Gokhfeld, D. M.; Altin, E.; Kurt, F.; Altin, S.; Demirel, S.; Aksan, M. A.
    Y-2/3 Se1/3Ba2Cu3Ox compound was fabricated by using solid state fabrication technique. Optimum heat treatments conditions for Y0.77Se0.33Ba2Cu3Ox were investigated. It was determined that the XRD results of these samples were similar to Y-123 phase with some impurities. Magnetization dependence of applied magnetic fields was measured in the range of 0-9 T at 10-50 K. The symmetric and asymmetric M-H loops were obtained for the samples. Magnetization loops obtained from measurements were successfully described by the extended Valkov-Khrustalev model. The temperature and applied magnetic field dependencies of magnetization of sample were estimated and critical current density of samples was calculated by Bean model and pinning force of samples was calculated by using Lorentz force. It is found from critical current density values that Se additions were acted as a pinning center which increased critical current density.
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    Magnetization loops and pinning force of Bi-2212 single-crystal whiskers
    (Elsevier Science Bv, 2011) Altin, S.; Gokhfeld, D. M.
    Dependence of magnetization on applied magnetic field for single-crystal Bi-2212 whiskers was measured at different temperatures. Symmetric and asymmetric magnetization loops were successfully described by the extended critical state model (the extended Valkov-Khrustalev model). Pinning force of whiskers was investigated. (C) 2011 Elsevier B.V. All rights reserved.
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    Physical, electrical, transport and magnetic properties of Nd(Ba,Nd)2.1Cu3O7-? system
    (Springer, 2013) Altin, E.; Gokhfeld, D. M.; Kurt, F.; Yakinci, Z. D.
    In this study, the superconducting Nd(Ba,Nd)(2.1)Cu3O7-delta system has been prepared using conventional solid-state reaction technique. Transport properties including structural/microstructural evolution, electrical, magnetic and critical current density properties were investigated. After high temperature heat treatments at over 1,000 A degrees C, large and strongly connected grains were obtained but weakly connected and small in size granular formation were obtained for the low temperature heat treated samples at around 900 A degrees C. The best T (c) and T (0) values were obtained as 93 and 89 K respectively for the sample prepared at 1,020 A degrees C for 24 h, which is very close to peritectic temperature of YBCO material. Magnetization of the sample heat treated at 1,020 A degrees C was investigated in detail. The magnetization hysteresis loops are expounded to be the product of Nd-123 grains and unscreened Nd3+ ions within intergranular boundaries and vortex cores. The peak effect on the magnetization curves was described by the extended critical state model. Temperature dependencies of the irreversibility field, the peak field and the full penetration field correlate and there is scaling behavior of the pinning force as well. Thermoelectric power data was analyzed by Modified two band model with linear T-term for superconductors. Temperature dependence of thermal conductivity of the samples showed small peak with broad maximum just below the T (c) value. Thermal conductivity of samples prepared was calculated by using The Modified Callaway Model and Wiedermann-Franz law and results obtained discussed.
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    Vortex pinning and magnetic peak effect in Eu(Eu,Ba)2.125Cu3Ox
    (Springer, 2014) Altin, E.; Gokhfeld, D. M.; Demirel, S.; Oz, E.; Kurt, F.; Altin, S.; Yakinci, M. E.
    Eu-Ba-Cu-O composition was synthesized by solid state reaction technique. To determine optimum growth temperature, heat treatment was examined on the material at 880-1,100 A degrees C. Microstructural evolution, phase formation and elemental distribution depending on heat treatments were examined by using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope analysis. Optimum fabrication conditions were determined as 1,020 A degrees C for 24 h under oxygen atmosphere and detailed characterization of corresponding compound was performed. The magnetization hysteresis loops are expounded to be the product of superconducting Eu-123 grains and magnetic Eu2+ ions. The peak effect on the magnetization curves was described by the extended critical state model. Scaling of the pinning force was found such that the peak position is proportional to the irreversibility field H (irr) and the maximum pinning force is proportional to H (irr) (2) .