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Öğe Enhancement of magnetic relaxation behavior by texturing in Bi-2212 superconducting rods(Elsevier Sci Ltd, 2016) Ozabaci, Murat; Kizilaslan, Olcay; Kirat, Gokhan; Aksan, Mehmet A.; Madre, Maria A.; Sotelo, Andres; Yakinci, Mehmet E.Time decay of magnetization, known as magnetic relaxation, is crucial for both fundamental and applied point of view in bulk high temperature superconductors (HTS) by setting the limits to the HTS devices stability. Melt-processed Bi2Sr2Ca1Cu2-xGa8+delta rods (Bi-2212, x=0,0.1) were used to study the effect of both grain alignment and substitution on the samples critical current density, relaxation and pinning behavior. The magnetic field has been applied both perpendicular and parallel to the rods growth axis to determine the effect of grain alignment. It has been found that Ga substitution reduces grains orientation and sizes leading to lower magnetic properties. The peaks of the curves, which indicate the temperature dependence of the samples magnetic relaxation rate (S), have been observed in the 7-35 K temperature range. Characteristic pinning energy (U-e/k(B)) of samples was determined using the formalism developed by Maley. The change of pinning energy as a function of magnetization has been found to be exponential between 3 and 60 K, which is in agreement with the collective creep theory. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Magnetocaloric Properties of Ni-Rich Ni50-xCoxMn38Sn12B3 Shape Memory Ribbons (vol 34, pg 581, 2021)(Springer, 2021) Kirat, Gokhan; Kizilaslan, Olcay; Aksan, M. Ali[Abstract Not Available]Öğe Magnetoresistance properties of magnetic Ni-Mn-Sn-B shape memory ribbons and magnetic field sensor aspects operating at room temperature(Elsevier Science Bv, 2019) Kirat, Gokhan; Kizilaslan, Olcay; Aksan, M. AliIn this study, the magnetotransport properties of the Ni48.95Mn37.74Sn13.32B3 ribbons prepared by melt-spinning technique were investigated in details. The martensitic-austenite phase transition was obtained between 280 K and 285 K which are near the room temperature. From rho-H measurements, it was found that an anomalous Hall effect at 281, 283 and 285 K between M-s (martensite start temperature) and M-f (martensite finish temperature) temperatures is domianant mechanism. It was seen that a voltage variation of 5 mu V (between 0 and 10 kOe) at a constant current of 1 mA is one of the best values found for the Heusler alloys. The rho-H results revealed that the ribbons showed the magnetic field-induced one-way shape memory effect (SME). High voltage change caused by magnetoresistance was reached at a constant current of 100 mA at 298 K. The results suggest that the Ni-Mn-Sn-B ribbon is a potential candidate to prepare a magnetic field sensor operating at the room temperature.Öğe Resonant Cavity Modes in Bi2Sr2CaCu2O8+x Intrinsic Josephson Junction Stacks(Amer Physical Soc, 2019) Zhang, Huili; Wieland, Raphael; Chen, Wei; Kizilaslan, Olcay; Ishida, Shigeyuki; Han, Chao; Tian, WanghaoWe report on a detailed investigation of terahertz-emission properties related to resonant cavity modes. We discuss data for an underdoped and an optimally doped Bi2Sr2CaCu2O8+x (BSCCO) intrinsic junction stack having the same geometry. At high bias, in the presence of a hot spot, the emission frequency seems to be continuously tunable by changing the bias current and the bath temperature. By contrast, at low bias the emission frequencies f(e) are remarkably discrete and temperature independent for both stacks. The values of f(e) point to the formation of (0, m) cavity modes with m = 3 to 6. The total voltage V across the stack varies much stronger than f(e), and there seems to be an excess voltage indicating groups of junctions that are unlocked. For the case of the underdoped stack we perform intensive numerical simulations based on coupled sine Gordon equations combined with heat-diffusion equations. Many overall features can be reproduced well and point to an unexpected large value of the in-plane resistivity. However, unlike in experiment, in simulations the different resonant modes strongly overlap. The reason for this discrepancy is presently unclear.Öğe Thermal and structural characterization of the Bi2-xSmxSr2Ca2Cu3O10+ glass-ceramic system(Wiley Periodicals, Inc, 2017) Kizilaslan, Olcay; Kirat, Gokhan; Aksan, Mehmet AliIn this work, investigations on the crystallization and oxidization kinetics of the Sm substituted BiSrCaCuO glass-ceramic system were performed. It has been shown that the Sm ions changed the glassification properties of the BiSrCaCuO system. While fully glass samples were obtained for low Sm-substitution levels (x=0.2 and x=0.4), the Sm containing particles on the surface have grown especially at high Sm-substitution levels (x>0.6) and glassification problem increased. Nonisothermal crystallization kinetics including activation energy for crystallization, E-a, and Avrami parameter, n, of the samples prepared was investigated using differential thermal analysis (DTA) at four different uniform heating rates. The values of glass transition temperature and crystallization temperature exhibited compositional and heating rate dependence. E-a value of the samples showed an increase with increasing the Sm concentration. The Avrami parameter, n, was found approximately 4.5, suggesting the growth of small particles with an increasing nucleation rate. The calculated values of the oxidization rates and the activation energy for oxygen out-diffusion process, E, indicated that the oxygen deficiencies by the Sm substitution in the unit cell of BiSrCaCuO were formed and more oxygen atoms were absorbed to fill the oxygen deficiencies in the system.Öğe Thermal hysteresis dependent magnetocaloric effect properties of Ni50-xCuxMn38Sn12B3 shape memory ribbons(Elsevier Sci Ltd, 2019) Kizilaslan, OlcayIn this study, the magnetocaloric effect in Ni50-xCuxMn38Sn12B3 ribbons depending on Cu substitution (x = 0, 1, 3) was investigated. The martensitic transition (MT) temperature of the ribbons shifted to lower temperatures with increasing Cu content. An inverse giant magnetocaloric effect (IMCE) was observed around the MT. Furthermore, the MT temperature of the x = 0 parent ribbon is around room temperature, which is important for technological applications. The Cu substitution helped to tune magnetization difference Delta M and hence the IMCE. The highest inverse magnetic entropy change Delta S-M(max) and the refrigerant capacity RC was obtained in the x = 1 Cu substituted ribbon. It is found that the inverse magnetic entropy changes Delta S-M were dependent on the thermal hysteresis. The average hysteresis losses (AHL) determined during cooling and heating processes were extremely different, indicating that the AHL is also thermal hysteresis dependent.
