Yazar "Kizilaslan, Olcay" seçeneğine göre listele
Listeleniyor 1 - 8 / 8
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Comparison of Long-Term Atmospheric Aging between Fe 3 O 4 and PEG-Protected Fe 3 O 4 Nanoparticles(Amer Chemical Soc, 2025) Erdogan, Ali; Kizilaslan, OlcayMagnetic nanoparticles have attracted significant attention due to their broad range of applications. A considerable amount of research has been conducted on the oxidation of Fe3O4 nanoparticles; however, there remains a significant lack of systematic data on the long-term oxidation mechanisms of these nanoparticles under ambient atmospheric conditions. A comprehensive one-year study was conducted to investigate the magnetic properties of uncoated and PEG-coated Fe3O4 nanoparticles. The systematic magnetization versus magnetic field measurements were performed over one year, with the samples stored under ambient atmospheric conditions and measured at regular intervals of a few weeks. To further characterize the synthesized nanoparticles, XRD, FTIR, and DLS analyses were conducted. The time-dependent oxidation process was modeled using an exponential function, and the fitting parameters were analyzed to provide physical insight into the oxidation behavior. The findings offer valuable perspectives on the potential applications of Fe3O4 nanoparticles, particularly in magnetically driven technologies across various fields, while also providing a deeper understanding of the slow oxidation mechanisms of uncoated and PEG-coated Fe3O4 nanoparticles.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 Terahertz emission from mutually synchronized standalone Bi2Sr2CaCu2O8+x intrinsic-Josephson-junction stacks(Amer Physical Soc, 2024) Wieland, Raphael; Kizilaslan, Olcay; Kinev, Nickolay; Dorsch, Eric; Guenon, Stefan; Song, Ziyu; Wei, ZihanSuitably patterned single crystals made of the cuprate superconductor Bi2Sr2CaCu2O8+x (BSCCO), intrinsically forming a stack of Josephson junctions, can generate electromagnetic radiation in the lower terahertz regime. Because of Joule heating, the emission power of single stacks seems to be limited to values below 100 mu W. To increase the radiation power, mutually synchronized arrays situated on the same BSCCO base crystal have been studied. A maximum power of almost 1 mW has been achieved by synchronization of three stacks. Mutual electromagnetic interactions via a connecting BSCCO base crystal have been considered essential for synchronization, but the approach still suffers from Joule heating, preventing the synchronization of more than three stacks. In the present paper we show, on the basis of two emitting stacks, that mutual synchronization can also be achieved by standalone stacks contacted by gold layers and sharing only a common gold layer. Compared with BSCCO base crystals, the gold layers have a much higher thermal conductivity and their patterning is not very problematic. We analyze our results in detail, showing that the two oscillators exhibit phase correlations over a range of +/- 0.4 GHz relative to their center frequencies, which we studied mainly between 745 and 765 GHz. However, we also find that strong phase gradients in the beams radiated from both the mutually locked stacks and the unlocked stacks play an important role and, presumably, diminish the detected emission power due to destructive interference. We speculate that the effect arises from higher-order cavity modes that are excited in the individual stacks. Our main message is that the mutual interaction provided by a common gold layer may open new possibilities for relaxing the Joule-heating problem, allowing the synchronization of a higher number of stacks. The approach may also allow one to synchronize several stacks that are comparatively small in size and less prone to the strong phase gradients we observed. Our findings may boost attempts to substantially increase the output power levels of BSCCO terahertz oscillators.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.
