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Öğe Bi-bazlı HTc süperiletkenlerde fiziksel özellikler ile birlikte termoelektrik güç ve termal iletkenlik karakteristiklerinin incelenmesi(İnönü Üniversitesi, 2003) Aksan, Mehmet AliBu çalışmada Bi2Sr2Ca2Cu3.xLxO104« (L=Mo (0.5Öğe BiSrCaCuO (222 3) cam-seramik süperiletken sistemin küçük yarıçaplı iyonların katılması ve sistemin fiziksel ve elektriksel özelliklerine etkilerinin incelenmesi(İnönü Üniversitesi, 1998) Aksan, Mehmet AliSüperiletkenlikte temel amaç geçiş sıcaklığı Tc' yi yukarıya çekmektir. Bu nedenle süperiletken sistemlere farklı elementler ilave edilmekte veya daha değişik kompozisyonlar hazırlanmaktadır. Bu çalışmada, cam-seramik yöntemi kullanılarak nominal kompozisyonu Bi2_ xGaxSr2Ca2Cu3O10+y ve Bi2.xZnxSr2Ca2Cu3O10+y (x=0.2, 0.4, 0.6, 0.8 ve 1.0) olan numuneler hazırlandı. Elde edilen amorf örnekler farklı periyotlarda ve sıcaklıkta ısıl işleme tabi tutuldu. Isıl işlem süresince meydana gelen mikroyapısal değişiklikler Diferansiyel Termal Analiz (DTA), X-Işınları Analizi (XRD), Taramalı Elektron Mikroskobu (SEM), Enerji Dağılımlı X-Işınları Analizi (EDAX) ve Direnç Sıcaklık Ölçümleri (R-T) ile analiz edildi. Analiz sonuçları galyum katılan sistemin kristal yapısında bir değişim olduğunu ve buna paralel olarak ta süperiletken özlliğinin azaldığını ortaya koymuştur. Çinko katılan sistemde ise kristal yapıda önemli bir değişiklik olmamakla birlikte süperiletkenlik özelliğinde azda olsa değişme ortaya koymuştur. Her iki katılma için BiSrCaCuO sisteminin üç fazı da, n=l, n=2 ve n=3, elde edilmiştir. Özellikle katkı miktarı arttıkça n=l fazına doğru değişim olmuştur. Cam olarak elde edilen her iki sistemin kristalleşme aktivasyon enerjileri de hesaplanmış ve değerler 260 ile 336 kJ/mol. arasında bulunmuştur. Sonuç olarak Bi iyonundan daha küçük yarıçaplı Ga ve Zn iyonlarının BiSrCaCuO sistemine katılması sistemin süperiletkenliğini olumsuz etkilemiştir. Anahtar Kelimeler: Süperiletkenlik, Bi temelli süperiletkenler, aktivasyon enerjisi, Cam-seramikler.Öğe GMI-based biosensor for the detection and quantification of doxorubicin anticancer drugs labeled to Fe3O4 superparamagnetic nanoparticles(Elsevier Science Sa, 2024) Kirat, Gokhan; Erdogan, Ali; Aksan, Mehmet AliWe present the results of research on a Co -based giant magnetoimpedance (GMI) biosensor for Fe 3 O 4 -labelled doxorubicin (DOX) anticancer drugs. Co 62 Fe 5 Ni 4 Si 15 B 14 ribbons were used as biosensing material for test solutions containing different concentrations of DOX. The plain ribbon, ribbon +Fe 3 O 4 and ribbon +DOX2 samples exhibited low coercivity ( H c ), high saturation magnetization ( M s ) and low anisotropy ( H k ). The GMI ratio ( Delta Z / Z ) increased from 33% to 38% with the increase of doxorubicin content in the ribbon. It was found that the Delta Z / Z ratio first increased rapidly up to a frequency of -2 MHz, and then decreased slowly as the frequency increased. While the magnetic field dependent Delta Z / Z has a single peak at 1 MHz, it has a double peak at 5 MHz. It was found that the peak height of Delta Z/Z in the ribbons with test solution of 20 ng/ml and 50 ng/ml increased by -3% and -6%, respectively, compared to the ribbon without test solution. Then the Delta Z / Z ratio decreased very rapidly with the increase of the applied external magnetic fields. The frequency -dependent GMI sensitivity ( eta) increased with increasing frequency and reached a maximum value at a critical frequency (-1.6 MHz), after which it decreased. The detection sensitivity of the GMI biosensor ( xi ) increased rapidly with increasing doxorubicin concentration up to -80 ng/ml and then remained almost unchanged. The results show that doxorubicin (DOX +Fe 3 O 4 ), used as an anticancer drug, can be effectively detected even at low concentrations using the GMI based sensors fabricated in this study.Öğe Investigation of magnetic and electrical properties in the Mo-substituted Ni-Mn-Sb Heusler alloys(Springer, 2023) Ayyildiz, Murat; Kirat, Gokhan; Aksan, Mehmet AliIn this study, Heusler alloys with nominal composition of Ni50-xMoxMn37Sb13+B2 (x = 0, 1, 3, 5, and 7) were synthesized by the arc-melting method. In the samples with low Mo-content, 4O and 10 M phases were obtained, indicating the presence of the martensite phase, while in the samples with high Mo-content, the L21 phase was determined, which is attributed to the austenite structure. The samples showed a two-step transition between T1 and T2 temperatures in the temperature dependent magnetization measurements, which is attributed to a premartensitic transformation. It was observed that the interval T1-T2 decreased with the increase of Mo-content in the system. It was found that there was an increase in magnetization value due to Curie transition around 350 K in x = 0 and x = 1 Mo-substituted samples, but there was no such increase between 5 and 360 K for other samples. It was found that the blocking temperature (TB) was affected by the Mo-substitution. The thermal hysteresis between the M-T curves during cooling and heating indicates a first-order phase transition in the samples. It is evident from both the M-T and rho-T analyses that the MT temperatures shifted to low temperatures as the Mo-content increases. An exchange bias effect was observed in the samples. increment SM with a positive sign was determined for all samples, reaching a maximum value around MT temperature. The maximum increment SM was obtained at a magnetic field of 5 T at 255 K in the x = 3 Mo-substituted sample. Similarly, the highest RC, AHL and RCeff values were also found for the x = 3 Mo-substituted sample.Öğe Investigation of martensitic transformation and magnetoresistance properties of cu-substituted Ni-Mn-Sn-B melt spun ribbons(Elsevier, 2021) Kirat, Gokhan; Aksan, Mehmet AliNi-50-xCu(x)Mn(38)Sn(12) + B3% at (x = 0, 1, 3 and 5) melt spun ribbons have been fabricated by melt spinning technique. Structural, electrical and magnetoresistance properties of the ribbons were investigated in this study. It was identified that the austenite phase with the L2(1) type structure was formed in the ribbons, regardless of composition. Temperature dependence of resistance measurements exhibited the first order martensite transition in the ribbons. The largest negative magnetoresistance (similar to 55%) was obtained at 262 K in the RB1 ribbon. Depending on the Cu-content and magnetic field, a noticeable shift of martensite transition temperature to low temperatures has been clearly observed. From magnetic field dependence of the resistance, it was seen that the resistances dropped sharply with the increase of the applied magnetic field and overlapped near 80 kOe, regardless of temperatures, which strongly indicates the magnetic field-induced martensite-austenite transition.Öğe Investigation on the transport and magnetism properties of the boron-substituted NiMnSb(Springer, 2023) Kilic, Gokhan; Abboosh, Omar; Kirat, Gokhan; Aksan, Mehmet Ali; Aydogdu, Ayse; Aydogdu, YildirimWe fabricated Ni46Mn41Sb13-xBx (x = 0, 1, 2, 3 and 4) (at.%) Heusler alloys using arc melting method and studied the electronic and magnetic properties of the alloys. It was seen that the martensite transformation temperatures shifted to higher temperatures with increasing the B-content in the system. It was found that for x less than 2, the alloys were in the austenite phase at the room temperature. However, when x is larger than 2, the crystal structure changed and a transformation to a martensite phase has occurred at room temperature. There were significant changes in lattice constants by boron substitution, which influenced the electrical and magnetic properties of the alloys. These changes are mainly related to the different atomic radius of Sb and B, which changed the atomic arrangement along a-axis. Hysteresis observed between the heating and cooling M-T curves obviously showed a field-induced martensitic transformation (FIMT) in the alloys. While the characteristic magnetization behavior of NiMnSb system was obtained at high magnetic fields, unstable magnetic behavior was observed at low magnetic fields. The boron substitution caused decrease in magnitude of the saturation magnetization (M-sat).Öğe Phase stabilization of magnetite (Fe3O4) nanoparticles with B2O3 addition: A significant enhancement on the phase transition temperature(Elsevier, 2016) Topal, Ugur; Aksan, Mehmet AliMagnetite nanoparticles (MNPs) are extensively investigated for biomedical applications, particularly as contrast agents for Magnetic Resonance Imaging and as drug delivery agent and heat mediators for cancer therapy. Tuning the magnetic properties of the magnetite nanoparticles with doping of foreign atoms has a crucial importance for determining the application areas of these materials and so attracts much interests. On the other hand the doping with foreign atoms requires high temperature annealing, and it causes a phase transition to the hematite phase above 400 degrees C. In this work the phase transition temperature from the magnetite to the hematite phase has been increased by 200 degrees C, which is the highest enhancement reported in literature. It was achieved by addition of the appropriate amounts of B2O3 Our experiments indicates that the 5.0 wt% of B2O3 addition stabilizes and keeps the existence of single phase magnetite up to 600 degrees C. (C) 2016 Elsevier B.V. All rights reserved.Öğe Süperiletken doğal (Öz) josephson eklem (IJJ) üretimi, karakterizasyonu ve teknolojik uygulaması(2012) Aksan, Mehmet Ali; Yakıncı, M.Eyyüphan; Aydoğdu, Yıldırım; Altın, Serdar[Abstract Not Available]Öğe Taşıyıcı Enjeksiyon Metodu ile Bi-Bazlı HT c Süperiletken Whisker lardan Hazırlanan Josephson Eklemlerde Süperiletkenliğin Ayarlanması(2016) Aksan, Mehmet Ali; Yakıncı, M.Eyyüphan; Kızılaslan, Olcay[Abstract Not Available]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.
