Yazar "Yakinci, Z. D." seçeneğine göre listele
Listeleniyor 1 - 10 / 10
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe 3D like vortex behavior and the thermally activated flux flow mechanism in (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting films(Springer, 2013) Yakinci, Z. D.; Altin, E.Approximately 1 mu m thick high quality epitaxial c-axis oriented (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting films have been prepared on MgO (100) substrates using spraying technique and post-Hg-Vapor annealing. The effect of the heating temperature-time combinations and the filling factor of Hg (ff(Hg)) on the physical, electrical and magnetic properties of the thick films have been investigated. The XRD investigations showed that the a-b plane of HgRe-1223 phase align parallel to the substrate surface. The best T (c) and T (zero) were found to be 130.6 and 127.2 K, respectively. The superconducting transition of the films has been measured under applied magnetic field up to 6 T. The results obtained suggested that dissipative resistivity can be explained by thermally activated flux motion below critical temperature under applied magnetic field. The temperature and field dependences of the activation energy in the thermally activated flux flow region have also been investigated. The calculated values of m and alpha values were found to be 1.42-1.49 and 0.498-0.518 respectively and suggesting a 3D like behavior and the thermally activated flux flow mechanism for all films fabricated. Magnetic properties of the films up to 6 T have also been investigated. The calculated value of critical current density, J (c), was found to be 4.7 x 10(6) A/cm(2) at 10 K for the optimally treated films.Öğe The effect of Sn content on mechanical, magnetization and shape memory behavior in NiMnSn alloys(Elsevier Science Sa, 2016) Aydogdu, Y.; Turabi, A. S.; Kok, M.; Aydogdu, A.; Yakinci, Z. D.; Aksan, M. A.; Yakinci, M. E.The effects of the composition alteration on the magnetization and shape memory behavior of Ni50Mn40-xSn10+x (x = 0, 1, 2, 3) alloys were systematically investigated by thermal, magnetic and mechanical experiments. Phase transformation from ferromagnetic austenite to weakly magnetic martensite was observed during thermal cycling under magnetic field and transformation temperatures were decreased with increasing Sn (or decreasing Mn). Moreover, the saturation magnetization of martensite increased with Sn content. Ni50Mn40Sn10 showed the recoverable strain of 2.1% during thermal cycling under 300 MPa and the reversible superelastic strain of 2% at 190 degrees C. Mechanical experiments exhibited that the largest compressive deformation of about 7% at 650 MPa occurred in Ni50Mn39Sn11 while Ni50Mn40Sn10 had fractured at 4% and 390 MPa at room temperature. (C) 2016 Elsevier B.V. All rights reserved.Öğe The effects of boron addition on the magnetic and mechanical properties of NiMnSn shape memory alloys(Springer, 2016) Aydogdu, Y.; Turabi, A. S.; Aydogdu, A.; Kok, M.; Yakinci, Z. D.; Karaca, H. E.The effects of boron addition on the microstructure, magnetic, mechanical, and shape memory properties of Ni50Mn40-xSn10Bx (at.%) (x = 1, 2, 3, 4, 6, 8) polycrystalline alloys were systematically investigated. It was revealed that transformation temperatures, magnetic behavior, mechanical, and shape memory properties can be tailored by B content. Transformation temperatures were decreased while saturation magnetization was increased with the addition of boron. In addition to magnetic behavior, ferromagnetic austenite transforms to weakly magnetic martensite, and then, martensite becomes ferromagnetic during cooling. The low amount of B addition (up to 4 %) to NiMnSn creates the second phase which provides higher strength and ductility. However, the high volume fraction of the second phase reduces the shape recovery because the phase transformation does not occur in the second phase. Brittleness takes place when the B amount is more than 6 % in NiMnSnB alloys. The amount of boron content in the NiMnSnB alloys plays a significant role to modify the magnetic, mechanical, and shape memory properties.Öğe 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.Öğe Magnetoresistance properties of MgB2 thick films on YSZ substrate using spray pyrolysis method(Iop Publishing Ltd, 2009) Altin, S.; Aksan, M. A.; Yakinci, Z. D.; Oezabaci, M.; Balci, Y.; Yakinci, M. E.The MgB2 thick films have been fabricated on the polycrystalline YSZ substrates using spray pyrlosis technique. Structural/microstructural, electrical and magnetic properties were investigated by XRD, SEM-EDX and R-T measurements. The films fabricated showed dense and homogenous structural formation with strong grain connections. The electrical properties of MgB2 thick films were investigated under different magnetic fields. It was seen that resistive transition broadened with increasing the applied magnetic fields. It was believed that the broadening is due to the thermally activated flux flow (TAFF). The activation energy, U(H), of the MgB2 films was calculated using Arhenius law.Öğe MgB2 thin film fabrication with excess Mg by sequential e-beam evaporation and transport properties under magnetic fields(Elsevier Science Bv, 2014) Altin, E.; Kurt, F.; Altin, S.; Yakinci, M. E.; Yakinci, Z. D.Superconducting MgB2 thin films with different thicknesses were fabricated by excess Mg using sequential electron beam evaporation technique. The flux rate of Mg and B were chosen as 3 nm/sn and 0.5 nm/sn respectively. The thickness of Mg/B layer was determined as 3/1 which causes an excess Mg for MgB2 formation. After two-step preparation process, the superconducting transition temperatures were found in the range of 32-37 K with a sharp transition to zero resistance state. The irreversibility fields, upper critical fields and activation energies were derived from magneto resistivity curves. The transport critical current densities of films were determined from I-V characteristics under different applied fields and the data was extrapolated for determination of value of the 0 K. (C) 2013 Elsevier B. V. All rights reserved.Öğe 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.Öğe Synthesis and Characterization of MgB2 Thin Films Prepared by 2.4 Mhz Ultrasonic Spray Pyrolysis System(Springer, 2011) Yakinci, Z. D.; Aydogdu, Y.Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al2O3(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB2 superconductors. After an in-situ heating process, similar to 600-1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM-EDX, R-T, and M-H analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB2 films were discussed. The best T (c) and T (zero) results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al2O3(001) substrates. Magnetic properties of the MgB2 films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum J(c)(mag) value was calculated to be 4.0x10(6) A cm(-2) at 10 K for 0 T for the film deposited on the Al2O3(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.Öğe Thermal and magnetic properties of Ni51Mn28.5Ga19.5B magnetic-shape-memory alloy(Springer, 2014) Kok, M.; Yakinci, Z. D.; Aydogdu, A.; Aydogdu, Y.Ni51Mn28.5Ga19.5B magnetic shape-memory alloy was produced in Arc melter under vacuum. The crystal structure of the produced alloy was determined by using XRD. The XRD analysis results indicated the presence of two phases; namely the martensitic phase that the alloy was determined to display non-modulated martensitic phase and the gamma phase characteristics. DSC was used to determine the transformation temperature, the thermodynamic quantities of martensitic transformation and the activation energy in the Ni51Mn28.5Ga19.5B alloy. The austenite transformation temperature and activation energy of transition were found as 46.92 A degrees C and 303.12 kJ mol(-1) respectively. The 1 % presence of the boron element in the alloy was observed to play a significant role in the transition temperature as indicated by the comparison of the values obtained in this study with those available in the literature. The magnetic properties of this alloy were determined using the PPMS instrument. The magnetic saturation value was determined as 66 emu g(-1).Öğe Thickness Dependence of Critical Current Density in MgB2 Films Prepared by Thermal Evaporation Method(Springer, 2011) Yakinci, Z. D.; Aydogdu, Y.MgB2 films with the thickness of 350 to 1150 nm have been prepared on the Al2O3 (001) single crystal substrates from high purity B and Mg powder by the thermal evaporation method. Films were then heat treated ex-situ under Mg vapor at 950 A degrees C to achieve actual MgB2 stoichiometry. Thickness of the films, so the deposition time, was varied to investigate its influence on critical current density of the films. The films fabricated were analyzed by means of microstructural, transport, and magnetic properties. The best T (c) and T (zero) values were obtained to be 39.5 K and 38 K, respectively, and decreased with increasing the thickness. We found that the critical current density of the films prepared is highly thickness dependent. The maximum J(c)(mag) value was calculated to be 3.18x10(6) A cm(-2) at 10 K and zero field for 1150 nm thick films but dropped drastically by thickness.
