Browsing by Author "Tekgül, Atakan"

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Changes in structural, magnetic and magnetocaloric properties due to homogenization annealing in Ni54Mn19Ga27
(Elsevier, 2019-01-01) Tekgül, Atakan; Şarlar, Kağan; Küçük, İlker; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi.; 0000-0001-6737-3838; 0000-0002-8871-2357; HWM-7283-2023; B-8159-2016; JJU-8757-2023; 37462175100; 55550817200; 6602910810
Structural and magnetic transformations in the Heusler system Ni54Mn19Ga27 due to different annealing time are studied by X-ray diffraction (XRD) and magnetization measurements. The developing of inter-martensitic and second order phase transition are investigated as a function of the annealing time. Analysis of the XRD data reveals that the austenite state has an L21 structure, whereas the structures of the martensite is a 14M (tetragonal) and the alloy crystallizes in the mixture phase at room temperature. In magnetic measurements, these martensite and austenite phases are ferromagnetic and due to ferromagnetic exchange caused different Curie temperatures for the austenitic and martensitic states in the sample with as prepared, 0.5 and 1 h except 5 h. The saturation magnetization changed from 35 to 68 A m2 kg−1 and the coercivity of these decreased from 1.8 to 0.3 mT as a function of annealing time. And also, the magnetic entropy change was determined to be 2.4 J kg−1 K−1 for as-prepared sample and 5.4 J kg−1 K−1 for 5 h sample. At 2 T magnetic field, the calculated relative cooling power (RCP) values for all alloys were found to be 85.8, 113.8, 120.8, 169.1 J kg−1 as annealing time increase. © 2018 Elsevier B.V.
Co/Cu çok katmanlı nanoyapılar üzerine Fe içeriğinin etkisi
(Uludağ Üniversitesi, 2010-01-13) Tekgül, Atakan; Alper, Mürsel; Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Fizik Anabilim Dalı.
Bu çalışmada CoFe/Cu ferromanyetik çok katmanlı yapılar elektrokimyasal sentezleme tekniği ile kendi iyonlarını içeren çözeltilerden Ti (hekzagonal sıkı paket, hcp) alt tabaka üzerine 3 mikrometre kalınlığında olacak şekilde büyütüldüler. Bu çok katmanlı filmlerin özellikleri, Fe konsantrasyonu, Cu ve CoFe tabaka kalınlığına göre incelendi. Metallerin depozisyon potansiyelleri, dönüşümlü voltametri (CV) tekniği ile referans elektroda (doymuş kalomel elektrot SCE) göre, CoFe için -1.5 V ve Cu için -0.3 V olarak belirlendi.Numunelerin, yapısal karakterizasyonları X-ışını difraksiyonu (XRD) tekniği ile yapıldı. Üretilen filmlerin XRD spektrumlarında yüzey merkezli kübik (fcc) yapının (111), (200), (220) ve (311) yansımalarından kaynaklanan pikler açık şekilde gözlendi ve bundan dolayı numuneler tek fazlı olarak fcc yapıda kristalleşmektedir. 0.0 M Fe 0.05 M ve 0.1 M konsantrasyonuna sahip çözeltilerden üretilen numunelerin kristal yönelimlerinin, bulk metallerinde olduğu gibi rastgele yönelime sahip olduğu bulundu. Fe içeriğinin 0.1 M'a kadar yükseltilmesi ile numunenin fcc fazının Fe'in cisim merkezli kübik (bcc) yapısından dolayı zayıfladığı görüldü.Filmlerin manyetik karakterizasyonları için titreşimli örnek magnetometresi (VSM) kullanıldı. Ölçüm sonuçlarında Fe konsantrasyonunun 0.0 M'dan 0.1 M'a kadar arttırılması ile filmlerin koarsivite değerlerinin azaldığı görüldü. Bu azalma, film içindeki depozit olan yumuşak ferromanyetik yapıya sahip Fe'den kaynaklanmaktadır. Bu da numunelerin koarsivite değerlerinin yumuşak ferromanyetik madde sınırı olan 12.5 Oe değerine doğru yaklaşmaktadır.Numunelerin manyetorezitans (MR) ölçümleri van der Pauw tekniği ile ölçüldü. CoFe/Cu katmanlı filmler, periyodik yapısından dolayı dev manyetorezistans (Giant magnetoresistance-GMR) etki göstermiştir. 0.0 M Fe konsantrasyonuna sahip çözeltiden üretilen 285[Co(6 nm)/Cu(4.5 nm)] numunesi (285 bilayer sayısına sahip), %10'luk bir GMR değerine sahip iken 0.05 M Fe içeren çözeltiden üretilen numune için bu değer %22'ye kadar çıkabilmektedir. Çözeltideki Fe konsantrasyonu, 0.05 M dan 0.4 M'a kadar olan çözeltilerden üretilen filmlerin GMR değerleri azalarak %3'e kadar düşmektedir. Ayrıca numunelerin magnetorezistans değerleri hem Cu hem de CoFe tabaka kalınlığına bağlı olarak ölçüldü. CoFe tabaka kalınlığı 6 nm de sabit tutularak Cu tabakası 0 dan 10 nm'ye 23 farklı kalınlıkta büyütüldü. En büyük GMR değeri Cu kalınlığı 4.5 nm olduğu zaman elde edildi. Diğer taraftan Cu kalınlığı 4 nm de sabit tutularak CoFe kalınlığı 3-15 nm ye kadar değiştirildi ve en büyük GMR değeri CoFe kalınlığı 6 nm olduğunda gözlendi.
The effect of Fe content in electrodeposited CoFe/Cu multilayers on structural, magnetic and magnetoresistance characterizations
(Amer Scientific Publishers, 2010-11) Koçkar, Hakan; Karaağaç, Öznur; Tekgül, Atakan; Alper, Mürsel; Şafak, Mürşide; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; AAG-8795-2021; 37462175100; 7005719283; 13613646100
A series of CoFe/Cu multilayers were electrodeposited on Ti substrates from the electrolytes containing their metal ion under potentiostatic control, but the Fe concentration in the electrolytes was changed from 0.0125 M to 0.2 M. The deposition was carried out in a three-electrode cell at room temperature. The deposition of Cu layers was made at a cathode potential of -0.3 V with respect to saturated calomel electrode (SCE), while the ferromagnetic CoFe layers were deposited at -1.5 V versus SCE. The structural studies by X-ray diffraction revealed that the multilayers have face-centered-cubic structure. The magnetic characteristics of the films were investigated using a vibrating sample magnetometer and their easy-axis was found to be in film plane. Magnetoresistance measurements were carried out using the Van der Pauw method at room temperature with magnetic fields up to +/- 12 kOe. All multilayers exhibited giant magnetoresistance (GMR) and the GMR values up to 8% were obtained.
Effect of l-ascorbic acid on electrochemically deposited fecocu/cu magnetic multilayer granular films: Structural, magnetic and magnetoresistance properties
(Elsevier, 2020-09-01) Şahin, Turgut; Koçkar, Hakan; ALPER, MÜRSEL; Tekgül, Atakan; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; 0000-0002-4862-0490; AAG-8795-2021; P-2124-2016
The FeCoCu/Cu multilayer granular films were prepared by the electrochemical deposition technique, and the effect of the L-ascorbic acid molarity on their structural, magnetic, and magnetoresistance properties was investigated. The structure of multilayer granular films is a face-centered cubic at room temperature, and the crystallite size increases from 5 to 14 nm with increasing the molarity of the L-ascorbic acid in the electrolyte. The recorded current-time curves indicate that 0.06 M L-ascorbic acid causes high current (200 mA) in the deposition of the magnetic layer during the electrochemical deposition process. The compositional analysis indicates that Fe deposition amount increases with increasing the L-ascorbic acid for the 0.04 and 0.06 M. The saturation magnetization decreases in the thin films due to increasing the molarity of L-ascorbic acid in the electrolyte. However, some of the Co and Fe reduces as a form of their oxide in the multilayer granular films containing a high amount of magnetic materials, and the antiferromagnetic behavior suppresses the ferromagnetic behavior. The multilayer granular film produced from the electrolyte with 0.04 M L-ascorbic acid exhibits both high magnetoresistance as 12% and 3.5% anisotropic magnetoresistance effect, and also, about 1 nm particle size.
The electrical characterization of electrodeposited Ni thin film on silicon: Schottky barrier diodes
(Natl Inst Optoelectronics, 2012) Tekgül, Atakan; Ahmetoğlu, Muhitdin; Alper, Mürsel; Kucur, Banu; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; AAG-8795-2021; 16021109400; 7005719283; 36903670200
A Ni/n-Si Schottky barrier diode was produced by electrodeposition technique from the electrolyte containing nickel ions under galvanostatic control. The deposition was carried out in a three-electrode cell at room temperature. The electrical characteristics of the Schottky diodes have been investigated using current-voltage (l-V) and capacitance-voltage (C-V) measurements. Ni/n-Si/AuSb diode current-voltage characteristics display low reverse bias leakage currents. The barrier height and ideality factor (n) were obtained 0.60 eV and 3.28 respectively. The high ideality factor value was attributed to oxide layer at the metal semiconductor interface.
Electrochemical deposition of CoCu/Cu multilayers: Structural and magnetic properties as a function of non-magnetic layer thickness
(Walter de Gruyter, 2018-02) Koçkar, Hakan; Kuru, Hilal; Tekgül, Atakan; Alper, Mürsel; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; AAG-8795-2021; 37462175100; 7005719283
Electrochemical deposition of CoCu/Cu multilayers was performed on titanium substrates from a single bath as a function of the Cu layer thicknesses. The deposition potentials were selected as -1.5 V for the magnetic layers and -0.3 V for the non-magnetic layers with respect to the saturated calomel electrode. The current-time transients were obtained during the deposition process, and the Co layer deposition and capacitive transients were calculated. On the basis of structural analysis, the multilayers were found to be polycrystalline with both Co and Cu layers adopting the face-centered cubic structure. The calculated lattice parameters of the multilayers slightly increase from 0.3585 to 0.3615 nm with increase in the Cu layer thickness, which is consistent with the bulk value of Cu. The inter-planar distance of the peaks of the multilayers is closer to that of Cu (d(111) = 0.2087 nm) and Co (d(111) = 0.2046 nm), and they become close to that of bulk Cu with increasing Cu layer thickness. In magnetic measurements, the magnetization decreases from 156 to 44 emu/cm(3) depending on the Cu layer thickness. Furthermore, the coercivity of the multilayers increases from 20 to 140 Oe. These values show that the magnetic behaviour of the multilayers lie between those of soft and hard magnetic materials, but the multilayer having 2.5 nm Cu layer thickness shows hard magnetic property. For the CoCu(4 nm)/Cu(0.7 nm) multilayer, the magnetoresistance measurement shows 5.5 % giant magnetoresistance (GMR).
Electrochemical, structural and magnetic analysis of electrodeposited CoCu/Cu multilayers: Influence of Cu layer deposition potential
(Springer, 2018-03) Koçkar, Hakan; Kuru, Hilal; Ünlü, Cumhur Gökhan; Tekgül, Atakan; Alper, Mursel; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; AAG-8795-2021; 37462175100; 7005719283
The electrochemical, structural and magnetic properties of CoCu/Cu multilayers electrodeposited at different cathode potentials were investigated from a single bath. The Cu layer deposition potentials were selected as , and with respect to saturated calomel electrode (SCE) while the Co layer deposition potential was constant at versus SCE. For the electrochemical analysis, the current-time transients were obtained. The amount of noble non-magnetic (Cu) metal materials decreased with the increase of deposition potentials due to anomalous codeposition. Further, current-time transient curves for the Co layer deposition and capacitance were calculated. In the structural analysis, the multilayers were found to be polycrystalline with both Co and Cu layers adopting the face-centered cubic structure. The (111) peak shifts towards higher angle with the increase of the deposition potentials. Also, the lattice parameters of the multilayers decrease from 0.3669 nm to 0.3610 nm with the increase of the deposition potentials from to , which corresponds to the bulk values of Cu and Co, respectively. The electrochemical and structural results demonstrate that the amount of Co atoms increased and the Cu atoms decreased in the layers with the increase of deposition potentials due to anomalous codeposition. For magnetic measurements, the saturation magnetizations, obtained from the magnetic curves of the multilayers were obtained as 212 kA/m, 276 kA/m, and 366 kA/m with , , and versus SCE, respectively. It is seen that the values increased with the increase of the deposition potentials confirming the increase of the Co atoms and decrease of the Cu amount. The results of electrochemical and structural analysis show that the deposition potentials of non-magnetic layers plays important role on the amount of magnetic and non-magnetic materials in the layers and thus on the magnetic properties of the multilayers.
Facile electrodeposition CoCu/Cu multilayers: Deposition potentials for magnetic layers
(Springer, 2016-11-18) Koçkar, Hakan; Kuru, Hilal; Tekgül, Atakan; Alper, Mürsel; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; 37462175100; 7005719283
The Co(Cu)/Cu magnetic multilayers were produced by electrodeposition technique as a function of the cathode potentials for magnetic layer deposition from a single bath. For proper depositions, cyclic voltammograms were used and the current-time transients were obtained. All potentials were determined with respect to saturated calomel electrode. The Co layers were deposited at cathode potentials of -1.3, -1.5 and -1.7 V, while -0.3 V was used for the Cu layers deposition. All multilayers were polycrystalline in the face-centred-cubic (fcc) structure with both Co and Cu layers adopting the fcc structure. The crystal structure of the multilayers is the same as fcc bulk Cu, but (220) peak splits the two peaks which are Cu(220) and Co(220). Both Co and Cu diffraction lines overlap in the (111) and (200) strong peaks and thus they seem to be a single peak. In the magnetisation measurements, the highest saturation magnetization was found to be 212 kA/m in producing with -1.5 V for Co deposition potential. The coercivities of multilayers are found to be 12.1, 16.9 and 18.3 kA/m for -1.3, -1.5 and -1.7 V cathode potentials, respectively.
Giant magnetoresistance in electrochemical deposited CoFe/Cu multilayers depending on Fe concentration
(Springer, 2017-11-28) Koçkar, Hakan; Tekgül, Atakan; Alper, Mürsel; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; AAG-8795-2021; 37462175100; 7005719283
Electrochemical deposition of CoFe/Cu multilayers were performed on Ti substrate from a single bath. 0.025, 0.05 and 0.1 M Fe concentration were used in electrolytes. The deposition potentials were selected - 1.5 V for magnetic layers and - 0.3 V for non-magnetic layers with respect to saturated calomel electrode. The current-time transients were obtained during the deposition process. The X-ray diffraction was used to define the structure of the multilayers. The multilayers were found to be face-centred cubic structure such as bulk Cu. Their lattice parameter and inter-planar distances values confirm this result. The magnetic measurements were performed at room temperature under 2 kOe external magnetic field. The results show that the saturation magnetization gradually increased from 27 to 50 emu/cm(3) with increasing 0.025 to 0.05 M Fe concentration in electrolyte, and in the multilayer prepared from the electrolyte containing 0.1 M Fe concentration, this value drastically decreased to 18 emu/cm(3). The magnetoresistance measurements were carried out in magnetic fields in the range of +/- 1.2 kOe. The high GMR value (18 %) and sensitivity (4.4 %/Oe) were obtained for this multilayer.
K dopant effect on La0.7KxCa0.3-xMnO3 (x=0, 0.05, 0.1) perovskite compounds: the structural, magnetic and magnetocaloric properties
(Springer, 2020-03-23) Unlu, Cumhur Gökhan; Tekgül, Atakan; Sarlar, Kağan; Küçük, İlker; KÜÇÜK, İLKER; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Psikoloji Bölümü.; 0000-0001-6737-3838; 0000-0003-2554-5886; 0000-0002-8871-2357; B-8159-2016; GXN-2736-2022; P-2124-2016
La0.7KxCa0.3-xMnO3 (x = 0, 0.05, 0.1) perovskites were prepared by sol-gel method. The K-doped effect was determined by the structural, magnetic, and magnetocaloric properties of the compounds. In the crystal structure of K-doped La0.7Ca0.3MnO3, Mn-O-Mn bond angle slightly increases with K addition. The transition shifts the range of 270-320 K when the K is added in La0.7Ca0.3MnO3. The Curie temperature increases from 251 to 288 K with increasing K amount. The maximum magnetic entropy change was found to be 2.7 J kg(-1) K-1 at 283 K under a magnetic field change of 2 T for the La0.7K0.05Ca0.25MnO3. The relative cooling powers (RCPs) in the La0.7KxCa0.3-xMnO3 (x = 0, 0.05, 0.1) samples were calculated to be 103, 133 and 88 J kg(-1), respectively.
La0.7Ca0.1K0.2MnO3 bileşiğinin manyetik akışkan hipertermi uygulaması
(Bursa Uludağ Üniversitesi, 2019-09-27) Tekgül, Atakan; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838
La0.7Ca0.1K0.2MnO3 nanoparçacıklar sol-gel yöntemiyle sentezlendi. Bileşiğin yapısal, manyetik ve manyeto-termal özellikleri detaylı bir biçimde incelendi. Yapısal özellikleri X-ışını kırınımı (XRD) ve taramalı elektron mikroskobu (SEM) ile gerçekleştirildi. XRD deseninde FullProf programı yardımıyla Rietveld analizi gerçekleştirildi. Analiz sonucunda bileşiğin kristal örgüsünün ortorombik yapıya sahip olduğu ve içerisinde La2O3, Mn3O4 ve MnO2 safsızlıklarının bulunduğu gözlendi. SEM analiziyle nanoparçacıkların küresele yakın bir geometriye sahip olduğu ve safsızlıkların altıgen ve küp şeklinde belirli bölgelerde oluştuğu görüldü. Manyetik analizlerin sonucunda bileşiğin oda sıcaklığında ferromanyetik kısmen paramanyetik duruma geçtiği görüldü. Ferromanyetik faza ait doyum mıknatıslanması 1,9 Am2 /kg ve bileşiğin koarsivite değeri 12 mT olduğu belirlendi. Manyeto-termal ölçümler sonucunda bileşiğin spesifik soğurma oranı (SAR) değeri 11,5 W/g olarak hesaplandı.
Magnetocaloric properties in a FeNiGaMnSi high entropy alloy
(Elsevier, 2019-09-30) Şarlar, Kağan; Tekgül, Atakan; Küçük, İlker; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; 0000-0002-8871-2357; FJG-9926-2022; 55550817200; 37462175100; 6602910810
We investigated a new Fe26.7Ni26.7Ga15.6Mn20Si11 high entropy alloy (HEA) without the rare earth element. The structural, magnetic and magnetocaloric properties of the resulting materials are presented. The HEAs successfully is produced by the arc melting with suction casting method. The crystal structures are characterised through multiphase Rietveld refinement of X-ray diffraction data. The structure of the HEAs was found to be the body centred cubic (bcc). In the magnetic measurements, the ferromagnetic to paramagnetic transition was obtained in the range of 300–400 K. With the employed suction casting method; the Fe26.7Ni26.7Ga15.6Mn20Si11 HEA shows the best magnetocaloric properties as 1.59 Jkg−1K−1 maximum magnetic entropy change (0–2 T) and 75.68 Jkg-1 refrigeration capacity after the annealing process.
Magnetocaloric properties of rare-earth-free mn27cr7ni33ge25si8 high-entropy alloy
(IEEE, 2019-11-26) Sarlar, Kağan; Tekgül, Atakan; Küçük, Ilker; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; 0000-0002-8871-2357; P-2124-2016; GXN-2736-2022; B-8159-2016; 55550817200; 37462175100; 6602910810
The magnetic and magnetocaloric properties of a new Mn27Cr7Ni33Ge25Si8 high-entropy alloy (HEA) were investigated. The crystal structure is characterized through multiphase Rietveld refinement of X-ray diffraction data. The structure of the HEA is orthorhombic in the Pnma space group. Arrott plots indicate that the ferromagnetic-paramagnetic phase transition is of second order. The maximum magnetic entropy change is 2.49 J.kg(-1).K-1, among the highest reported for alloys that do not contain rare earth elements.
Magnetoresistance behaviour in CoFe/Cu multilayers: Thin Cu layer effect
(Springer, 2016-05-26) Koçkar, Hakan; Tekgül, Atakan; Alper, Mürsel; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; AAG-8795-2021; 37462175100; 7005719283
The magnetoresistance properties of the CoFe/Cu multilayers have been investigated as a function of thin non-magnetic Cu layer thickness (from 2.5 to 0.3 nm). CoFe/Cu multilayers were electrodeposited on Ti substrates from a single electrolyte containing their metal ions under potentiostatic control. The structural analysis of the films was made using X-ray diffraction. The peaks appeared at 2 theta ae 44A degrees, 51A degrees, 74A degrees and 90A degrees are the main Bragg peaks of the multilayers, arising from the (111), (200), (220) and (311) planes of the face-centered cubic structure, respectively. The magnetic characterization was performed by using vibration sample magnetometer in magnetic fields up to +/- 1600 kA/m. At 0.6, 1.2 and 2.0 nm Cu layer thicknesses, the high saturation magnetization values were observed due to antiferromagnetic coupling of adjacent magnetic layers. Magnetoresistance measurements were carried out using the Van der Pauw method in magnetic fields up to +/- 1000 kA/m at room temperature. All multilayers exhibited giant magnetoresistance (GMR), and the similar trend in GMR values and GMR field sensitivity was observed depending on the Cu layer thickness.
Narrow transitional hysteresis in (Mn -Cr-Co) 2 Sb pnictides for room-temperature magnetic refrigeration
(Publishing, 2019-04-10) Tekgül, Atakan; Acet, Mehmet; Scheibel, Franziska; Farle, Michael; Tekgül, Atakan; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü; 0000-0001-6737-3838; P-2124-2016
Mn1.96-xCrxCo0.04Sb with x = 0.05 and 0.09 has been investigated for its magnetocaloric properties using structural, magnetization and calorimetric methods. These compounds exhibit an antiferromagnetic-ferrimagnetic transition of which the temperature can be adjusted by the Cr concentration. The transition temperature is at room temperature for x = 0.09. Magnetocaloric properties are presented as entropy-change and direct temperature-change. We show that these compounds have a narrow transitional hysteresis and exhibit the inverse magnetocaloric effect. We find a nearly hysteresis-free transition with a 2.6 K temperature-change around 287 K making it attractive for magnetic-cooling.
Optimization of fe content in electrodeposited fecocu/cu magnetic multilayer
(Elsevier, 2019-03-01) Koçkar, Hakan; Tekgül, Atakan; Alper, Mürsel; ALPER, MÜRSEL; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi; 0000-0001-6737-3838; 0000-0002-4862-0490; P-2124-2016; AAG-8795-2021
The structural, magnetic and magnetoresistance properties of FeCoCu/Cu multilayers prepared by electrochemical deposition from a single bath containing 0.025, 0.05 and 0.1 M Fe under potentiostatic control are investigated. The deposition potentials were selected - 1.5 V for magnetic layers and - 0.4 V for non-magnetic layers concerning saturated calomel electrode. The multilayers exhibited face-centered-cubic structure in the X-ray diffraction. In the multilayer produced from the electrolyte containing 0.05 M Fe, the high saturation magnetization value (572.3 kA/m) was observed and it value drastically decreased 140.6 kA/m in the electrolyte containing 0.1 M Fe. The magnetoresistance measurements were carried out in magnetic fields in the range of +/- 955 kA/m. The high giant magnetoresistance value (18.7%) were obtained in the multilayer with 0.05 M Fe. In the magnetic sublayers of the multilayers, the more than Cu atoms deposited and due to this, the magnetoresistance curves exhibited the 2.5, 4.7, 2.4% anisotropic magnetoresistance contributions between longitudinal and transverse magnetoresistance.
The production of Cu nanoparticles on large area graphene by sputtering and in-flight sintering
(Wiley-V C H, 2017-11) Ünlü, C. Gökhan; Acet, Mehmet; Farle, Michael; Atakan, Şaban; Lindner, Jürgen; Tekgül, Atakan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; P-2124-2016; 37462175100
We have developed a simple method to synthesize Cu nanoparticles on graphene, which is a composite that is currently investigated for use as biosensors. Firstly, large area graphene (2 x 2 cm(2)) was prepared by chemical vapor deposition on Cu foils and then transferred onto SiO2 substrates by a transfer process. The Cu nanoparticles were collected on graphene/SiO2 by magnetron sputtering. The presence of graphene was verified by optical microscopy and Raman spectroscopy. The structure of graphene decorated with Cu nanoparticles was determined by scanning and transmission electron microscopy. The results show that the Cu nanoparticles acquire a cubic structure on graphene
Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses
(Elsevier, 2016-06-15) Koçkar, Hakan; Alper, Mürsel; Tekgül, Atakan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0001-6737-3838; AAG-8795-2021; P-2124-2016; 7005719283; 37462175100
The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3 nm to 10 nm using electrodeposition. By now, the thinnest Cu (0.5 nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current-time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of -0.3 and -1.5 V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600 kA/m from 3 to 8 nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8 nm of the CoFe layer thickness. It is seen that the thin Cu layer(fixed at 0.5 nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance(GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices.
Structural and magnetocaloric properties of feni high entropy alloys
(IOP Publishing, 2021-12-01) Sarlar, Kağan; Tekgül, Atakan; Küçük, Nil; Etemoğlu, Akın Burak; Tekgül, Atakan; KÜÇÜK, NİL; ETEMOĞLU, AKIN BURAK; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0001-6737-3838; 0000-0002-9193-4591; 0000-0001-8022-1185; ABE-9423-2020; GXN-2736-2022; AAI-6808-2021
In this study, a new Fe30.7Ni25.7Ga14.6Mn19Si10 without rare earth element high entropy alloy's (HEA) magnetocaloric properties was investigated. The HEA was formed by the suction-casting method. x-ray diffraction (XRD) method was performed for structural analysis. XRD analysis show that both the as-quenched and annealed alloy have a single body centred cubic(bcc) structure. The result obtained from the Arrott plots indicates that the alloys have the second order magnetic phase transition. The transition temperature from paramagnetic to ferromagnetic transition was observed at 442 K and 462 K for the as-quenched and annealed alloy, respectively. The Fe30.7Ni25.7Ga14.6Mn19Si10 HEA shows magnetic entropy change such as 0.75 Jkg(-1) K-1 for as-quenched alloy, 0.90 Jkg(-1) K-1 for annealed alloy at 2 T magnetic field.
Structural, magnetic and GMR properties of FeCo(Cu)/Cu magnetic multilayers electrodeposited at high cathode potentials of the magnetic layer
(Natl Inst Optoelectronics, 2020-03-01) Tekgül, Atakan; Şahin, T.; Koçkar, H.; Alper, Mürsel; Tekgül, Atakan; ALPER, MÜRSEL; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü; 0000-0001-6737-3838; AAG-8795-2021; P-2124-2016
Structural, magnetic and giant magnetoresistance properties of the electrochemically deposited FeCo(Cu)/Cu multilayers at the various cathode potentials for magnetic layers were investigated. The cathode potentials were -1.8, -2.0, -2.5 and -2.8 V for magnetic layers and -0.3 V for non-magnetic layers with respect to a saturated calomel electrode. The multilayers have a face-centred-cubic structure. The obtained composition was found to be close the nominal composition at -2.8 V cathode potential. The highest giant magnetoresistance value (16.50 %) was obtained in the multilayer produced at -1.8 V. The highest sensitivity was found in the multilayer produced at -1.8 and -2.8 V.