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Öğe Effect of Co addition on the critical current density of MgB2 superconductor(Elsevier, 2014) Kirat, G.; Kizilaslan, O.; Aksan, M. A.; Yakinci, M. E.In this study, the (MgB2),Co-1-x(x), samples, where x-0.0. 0.1, 0.3, 0.6 and 0.8, were prepared by using the solid-state reaction technique. Effect of the Co-addition on the structural, magnetic, critical current density. J(c), and flux pinning properties of the superconducting MgB2 system was investigated. A magnetic transition was observed with increasing the Co-concentration in MgB2. For the pure MgB2, J(c), was obtained to be 2.78 x 10(4) A cm(-2) at 5 K and 1.7 kOe, but J(c) was suppressed by addition of Co to the system. It was found that a large amount of Co in MgB2 did not act as pinning centers which improves J(c) The magnetic behavior observed by the Co-addition originates from the magnetic properties of cobalt itself. (C) 2014 Elsevier B.V. All rights reserved.Öğe Effect of the Er-substitution on critical current density in glass-ceramic Bi2Sr2Ca2(Cu3-xErx)O10+? superconducting system(Elsevier Sci Ltd, 2016) Kirat, G.; Kizilaslan, O.; Aksan, M. A.Bi2Sr2Ca2Cu3-xErxO10+delta (x=0.0, 0.5 and 1.0) samples were manufactured using conventional glass ceramic technique and their structural, magnetic and flux pinning properties were studied. The onset temperature of diamagnetic signal decreased by the Er-substitution. The x=0.5 Er-substituted sample showed perfect diamagnetism, which is attributed to secondary phases acting as pinning centers in the crystal structure. J(c) of the samples was calculated by using Bean's equation. The highest J(c) value was obtained for x=0.5 Er-substitution. The results suggest that the Er ions in the host material act as pinning centers which lead to the increase of J(c). (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe The effects of substituting B for Cu on the magnetic and shape memory properties of CuAlMnB alloys(Springer Heidelberg, 2016) Aydogdu, Y.; Turabi, A. S.; Aydogdu, A.; Vance, E. D.; Kok, M.; Kirat, G.; Karaca, H. E.The effects of B addition on the magnetization, mechanical and shape memory properties in Cu70-xAl24-Mn6Bx at.% (x = 0, 1, 2, 3, 4) alloys have been investigated. The ductility was decreased, while the strength was improved with B addition. Transformation temperatures were increased with B content due to increased e/a ratio. Martensite start temperature of B-free CuAlMn was found to be 37.3 degrees C and increased to 218.8 degrees C with 4 % B addition. B-free CuAlMn exhibited shape memory effect with a recoverable strain of 2.25 % under 200 MPa and a perfect superelasticity with a recoverable strain of 2.5 % at 163 degrees C. B addition degraded the shape memory properties and eventually resulted in the lack of recoverable strain. In addition, saturation magnetization was increased with B content. Moreover, the addition of B slightly decreased the ductility of the alloy. It was found that the magnetization, mechanical and shape memory properties CuAlMn alloys can be tailored by quaternary alloying with B.Öğe Influence of coronene addition on some superconducting properties of bulk MgB2(Springer, 2018) Erdem, O.; Kirat, G.This study reports the effect of coronene (C24H12) addition on some superconducting properties such as critical temperature (T (c) ), critical current density (J (c) ), flux pinning force density (F (p) ), irreversibility field (H (irr) ), upper critical magnetic field (H (c2) ), and activation energy (U (0) ), of bulk MgB2 superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB2 samples with varying C24H12 contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 A degrees C in Ar atmosphere. The obtained results show an increase in field-J (c) values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (T (c) ) because of C substitution into MgB2 lattice, with increasing amount of C24H12 powder. The H (c2) (0) and H (irr) (0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. The U (0) depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U (0) values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. As a result, the superconducting properties of bulk MgB2 at high fields was improved using C24H12, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB2 structure.Öğe Influence of the Cu substitution on magnetic properties of Ni-Mn-Sn-B shape memory ribbons(Springer Heidelberg, 2021) Kirat, G.; Aksan, M. A.The Heusler alloy Ni50-xCuxMn38Sn12+B-y (x=0, 1, 3 and 5) was successfully produced in ribbon form using melt spinning technique. The magnetic properties of the obtained ribbons were analyzed in detail. In all ribbons, it was detected that the ferromagnetic austenite phase transformed into the weak magnetic martensite phase. A separation between FC and ZFC curves at lower temperatures was found. An increase in the magnetization in FC mode can be attributed to the coexistence of ferromagnetic (FM)/antiferromagnetic (AFM) at martensitic phase. It was found that the transition temperatures shifted to low temperatures with increasing the Cu content. The magnetization results under high magnetic field (10 kOe and 50 kOe) showed a thermal hysteresis between the cooling and heating cycles, which is clear evidence for a first-order transformation in the ribbons. From M-H data, all the ribbons exhibited ferromagnetic behavior at low temperatures below the martensitic transition temperature and paramagnetic behavior at high temperatures above the transition temperature. The results provide us a comprehensive view to reveal the effect of the Cu substitution on the magnetic properties of Ni-Mn-based shape memory ribbons.Öğe Magnetic field induced martensitic transition in Fe doped Ni-Mn-Sn-B shape memory ribbons(Elsevier Sci Ltd, 2019) Kirat, G.; Aksan, M. A.; Aydogdu, Y.In this study, effect of the Fe-doping on the microstructural evolution, phase transformation and magnetoresistance properties of the Ni-Mn-Sn-B magnetic shape memory ribbons fabricated by melt-spinning technique were investigated. While the phase transition temperatures from austenite to martensite in the undoped ribbon was very close to room temperature, it was found that they decreased by the Fe-doping, which was attributed to decrease in the e/a value with the Fe-content. A voltage change of 5 mu V at a constant current of 1 mA and at 283 K and in the magnetic range of 0-10 kOe was obtained, which is good value obtained for the Heusler alloys. The resistivity data measured in the martensitic - austenite transition region was overlapped at similar to 90 kOe, which is clear evidence for the magnetic field-induced one way martensitic transition. The ribbons showed an antiferromagnetic behavior at low magnetic field and a ferromagnetic behavior at high magnetic fields. The Fe-doping to the Ni-Mn-Sn system caused a significant increase in the magnitude of the magnetization. The results showed that the melt-spinning technique used in the production of magnetic shape memory strips is very promising for magnetic sensor applications.Öğe Magnetic Field-Induced Martensitic Phase Transition in Cr-Substituted Ni-Mn-Sb plus B Shape Memory Alloys(Springer Int Publ Ag, 2024) Ayyildiz, M.; Kirat, G.; Aksan, M. A.In this paper, the Ni50-yCryMn37Sb13 + B-2 (y = 0, 3, 5 and 7) Heusler system was fabricated by the conventional arc-melting method. Samples with low Cr-content (y = 0 and 3) exhibited a mixed phase of 4O and 10 M at room temperature, while the samples with y = 5 and 7 Cr-content crystallized to L2(1) phase with Fm (3) over barm space group. The martensitic transition temperature decreased with increasing Cr-content in the system. The temperature-dependent magnetization results at a magnetic field of 100 Oe revealed an intermartensitic phase transition. The temperature-dependent magnetization measurements under 10(4) Oe (1 T) demonstrated a phase transition from ferromagnetic austenite to weakly magnetic martensite between 300 and 200 K, depending on the substitution level. The presence of hysteresis in the M-H curves confirmed a magnetic field-induced transformation in the samples. The field cooled (FC) M-H hysteresis loops shifted to the negative axis, which indicates exchange bias (EB) effect in the samples. Arrott plots provided evidence for a first-order magnetic phase transition in the fabricated samples.Öğe Magnetic properties of the glass-ceramic Mg2-xMxAl4Si5O18 (M=Ni and Fe) system(Elsevier Sci Ltd, 2014) Kirat, G.; Aksan, M. A.In this study, Mg2-xMxAl4Si5O18 (M=Ni and Fe and 0 <= x <= 1.0) samples were fabricated by a glass ceramic technique using an arc-melter system. The glass samples were converted into the glass ceramic form under appropriate heat treatments. The structural, microstructural and magnetic properties of the samples were investigated by means of XRD, SEM-EDX, M-T, and M-H. Structural/microstructural analysis showed that multiphase and completely deformed structure was formed as a result of the substitutions. Surprisingly, the unsubstituted sample showed a magnetic behavior. The magnetization sharply increased with increasing the Ni and Fe-concentration in the system and the samples exhibited ferromagnetic behavior. It is believed that this is the result of the increased magnetic interactions between the substituted atoms. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Magnetic relaxation behavior in the Bi2Sr2Ca2Cu3-xMoxO10+? system fabricated by glass-ceramic technique(Elsevier, 2015) Kizilaslan, O.; Kirat, G.; Aksan, M. A.In this paper, we present a study on the critical current density and magnetic relaxation behavior of the Mo-substituted BiSrCaCuO system. The Bi2Sr2Ca2Cu3-xMoxO10+y, where x=0, 0.5, 1.0 and 1.5 have been fabricated using glass-ceramic technique. It was found that the Mo-substitution to the BiSrCaCuO system lead to the formation of pinning centers and hence an increase of critical current density. The magnetic relaxation experiments were performed to understand physical phenomena behind of flux motion. Time dependence of the magnetization exhibited thermally activation flux motion in the samples. It was found that the normalized magnetic relaxation rate, S. did not vary linearly with temperature, especially at high temperatures, which is attributed to the collective creep theory. In addition, the characteristic pinning energy, U-e/K-B, in the samples was calculated using Maley's method. Correlation between the pinning energy and the magnetization showed that obtained experimental results can be fitted to the collective creep theory. (C) 2015 Elsevier B.V. All rights reservedÖğe Observation of magnetic behavior at low temperature in the Mg2Al4Si5O18 system(Elsevier Science Sa, 2013) Kirat, G.; Aksan, M. A.The Mg2Al4Si5O18 materials were prepared by the melt-quenching technique using an arc-melter system. The heat treatments of the samples were performed at 1300 degrees C for 48 h and 72 h. From XRD analysis, while major phase in the samples was the alpha-cordierite, the MgAl2O4 (spinel) and MgO phases were also detected. It was observed that the uniformly distributed rods are formed perpendicular to the sample surface. EDX analysis revealed that the atomic composition of the rods is Mg2Al4Si5O18. The samples exhibited diamagnetic behavior at 300 K and the magnetization increased sharply at 25 K, suggesting a ferromagnetic or ferrimagnetic transition. This type of the magnetic behavior originates from minor crystalline phases, such as MgO and MgAl2O4. (C) 2013 Elsevier B.V. All rights reserved.Öğe Preparation and characterization of CaO-Al2O3-SiO2 (CAS) glass-ceramics(Elsevier, 2016) Ozabaci, M.; Aksan, M. A.; Kirat, G.; Kizilaslan, O.; Yakinci, M. E.A glass-ceramic CaO-Al2O3-SiO2 (CAS) system with CaAl2Si2O8 (Anorthite) composition was prepared at two different heat treatment temperatures following the melt-quenching in an arc-melter system. Structural and magnetic properties of the samples were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and magnetic measurements (M-H, M-T). A clear phase transformation, hexagonal to triclinic, was obtained when heat treatment temperature increased from 930 degrees C to the 1100 degrees C Two different impurity phases were obtained for the sample heat treated at 930 degrees C, but then these phases dissolved in the main matrix when temperature increased to 1100 degrees C and single phase CaAl2Si2O8 was obtained. All the samples showed diamagnetic behavior between room temperature and similar to 150 K, but then ferri- or ferromagnetic phase transformation was obtained. This transformation is found to be independent from the heating temperature and believed to be associated with the trapping of free electrons at crystal imperfections and cation ordering between Al and Si in the main matrix. (C) 2016 Elsevier B.V. All rights reserved.Öğe Role of the Fe-substitution in dielectric behavior of the glass-ceramic cordierite Mg2Al4Si5O18 system(Elsevier Science Bv, 2014) Kirat, G.; Aksan, M. A.In this study, Mg2-xMxAl4Si5O18, where M=Fe and x=0.0, 0.20, 0.50,1.0 and 1.5, have been synthesized using an arc-melter system. As a result of Fe-substitution, complex, deformed and multiphase samples were obtained. Microstructural analysis indicated that crystals of alpha-cordierite disappeared in the x=1.5 Fe-substituted sample. However, more densified samples than the unsubstituted sample were obtained. Dielectric constant increased gradually and capacitive resistance decreased with increasing the Fe-content in the system. The results suggested that the Mg2Al4Si5O18 materials obtained by the Fe-substitution are not suitable for high frequency applications. (C) 2014 Elsevier B.V. All rights reserved.Öğe Structure, Magnetic and Magnetoresistance Properties of Co62Fe5Ni4Si15B14 Amorphous Ribbons(Maik Nauka/Interperiodica/Springer, 2022) Kirat, G.Co-based ribbons were produced by melt spinning method and annealed at different temperatures. The XRD studies revealed that the melt spun ribbon was phase amorphous, whereas crystallization has appeared for the sample annealed at 600 degrees C. The results demonstrated that optimum magnetic softness corresponded to amorphous state of the sample annealed at 340 degrees C. Electrical resistance measurements based on temperature and magnetic field were discussed in details.
