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Öğe Challenges in electrical detection of spin-orbit torque in Ir20Mn80/Pt hetero-structures(Ios Press, 2023) Goksal, Ilkin; Piskin, Hasan; Kocaman, Bayram; Akin, Kutay; Cay, Dogukan; Selvi, Ege; Karakas, VedatManipulation of antiferromagnetic sublattice orientations, a key challenge in spintronic device applications, requires unconventional methods such as current induced torques including Spin Transfer Torque (STT) and Spin-Orbit Torque (SOT). In order to observe the deviation of the Neel vector from the anisotropy axis, one of the simplest approaches is the electrical detection, whereby one monitors the change in resistance as a function of applied current. In this work, we have investigated the conditions under which an ultra-thin metallic antiferromagnet, Ir20Mn80 becomes susceptible to SOT effects by studying antiferromagnetic layer structure and thickness dependence in antiferromagnetic metal (Ir20Mn80)/heavy metal (Pt) superlattices. Our electrical measurements reveal that in bilayer structures there exists a shallow range of Ir20Mn80 thicknesses (similar to 1-2 nm) for which SOT driven control of spins is apparent, whereas for lower thicknesses incomplete sublattice formation and for higher thicknesses improved thermal stability prohibits vulnerability to spin currents. Furthermore, in multilayers, structural changes in Ir20Mn80 layer quenches local torques due to stronger (111) magnetocrystalline anisotropy. These results suggest that an exhaustive optimization of the antiferromagnet parameters is crucial for the successful deployment of spintronic devices.Öğe Correlation of blocking and Néel temperatures in ultrathin metallic antiferromagnets(Amer Physical Soc, 2024) Akin, Kutay; Piskin, Hasan; Selvi, Ege; Demircanli, Emre; Ari, Sevval; Zadeh, Mohammad Hassan Ramezan; Kocaman, BayramNonvolatile spintronics-based devices that utilize electron spin both to store and transport information face a great challenge when scaled to nanosized dimensions due to loss of thermal stability and stray field- induced disturbance in closely packed magnetic bits. The potential replacement of ferromagnetic materials with antiferromagnets may overcome some of these issues owing to the superior robustness of sublattice spin orientations to magnetic field disturbance as long as they are kept well below the N & eacute;el temperature, which is hard to measure with conventional methods, especially in the ultrathin limit. In this work, we have employed spin pumping from a soft ferromagnetic NiFe layer into widely used ultrathin metallic antiferromagnet Ir20Mn80, 20 Mn 80 , FeMn, PtMn, PdMn, or NiMn with thicknesses in the 0.7-3 nm range, as a probe to detect damping enhancement during magnetic phase-transitions. Independent measurements of the blocking temperature with magnetometry reveal that temperature-dependent shifts in the resonance peaks can also be used to measure the blocking temperature, enabling the analysis of the correlation between the N & eacute;el and blocking temperatures in trilayers with the permalloy and antiferromagnetic layer separated by a 3-nm-thick spacer layer. The thickness-dependent characterization of thermal stability in antiferromagnets provides a key element for scalable and ultrafast antiferromagnetic spintronics.Öğe Dependence of exchange bias and coercive field on Cu spacer thickness in oblique deposited Co/Cu/CoO multilayers(Elsevier, 2021) Kocaman, Bayram; Aktas, Kubra Yildiz; Basaran, Ali C.Effect of growth-induced uniaxial anisotropy and thickness of non-magnetic Cu spacer between the ferromagnetic/antiferromagnetic Co/CoO multilayers on the exchange bias, coercive field, and magnetic anisotropy have been studied in 10?300 K temperature range. Co(8 nm)/Cu(tCu)/CoO(4 nm) (tCu = 0.6?2.6 nm) multilayers on Si (100) substrates were prepared using the oblique-angle magnetron sputtering deposition to induce growth induced magnetic anisotropy. The top Co layer was allowed to be naturally oxidized to obtain antiferromagnetic CoO. The films show a strong uniaxial in-plane anisotropy determined by ferromagnetic resonance measurements. Magnetization measurements for both easy and hard magnetization directions revealed that the exchange bias and coercive fields decrease by increasing Cu thickness. The existence of strong exchange bias across the thickest Cu layer shows the long-range character of exchange and dipolar interactions at 10 K. Dependence of Cu spacer thickness shows an oscillatory behavior that can be ascribed to the competitions between Ruderman?Kittel?Kasuya?Yosida (RKKY) and dipolar interactions.Öğe Magnetic and Electrical (GMR) Properties of Rh(IrMn)/Co/Cu/Ni(Py) Multilayered Thin Films(Springer, 2020) Aktas, Kubra Yildiz; Kocaman, Bayram; Basaran, Ali C.The magnetic and magnetoresistance properties of multilayered structures consisting of two different combinations of magnetic and nonmagnetic IrMn, Co, Cu, Ni, Py thin layers were studied in the temperature range of 10-300 K. Thin films were prepared by using conventional magnetic sputtering techniques in ultra-high vacuum conditions. The structural characterization was examined by X-ray reflectivity. Magnetic and electrical properties were studied by conventional dc magnetization and 4-probe resistivity measurements. A close relationship between magneto resistivity and the relative behavior of magnetic hysteresis of adjacent magnetic layers was observed. Very abrupt stepwise changes at coercive field regions of the soft magnetic layers were attributed to the so-called giant magnetoresistance effect at low temperatures in both combinations of the layers.Öğe Magnetic and structural characterization of Ni(1-x)Gex thin film(Journal of Magnetism and Magnetic Materials, 2015-01-01) kazan, sinan; Kocaman, Bayram; parabaş, adem; yıldız, fikret; aktaş, BekirIn this study, the growth and magnetic properties of Ni(1-x)Gex thin films on naturally oxidized Si(100) substrate by a molecular beam epitaxy (MBE) technique were investigated. The surface morphology and structural properties of the thin films were investigated by scanning electron microscopy (SEM) and X-ray diffraction techniques. The magnetic properties of the films were measured by ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. SEM images show that the morphology of the films depends on chemical composition of the films. The analysis of FMR spectra and VSM results shows that the saturation magnetization, coercive field and effective magnetization of Ni(1-x)Gex film decrease with the increase of Ge content up to a certain value (atomic percent of Ge at 9%) which is called critical Ge concentration. The magnetization dynamics and agglomeration of NiGe thin film with varying Ge concentration have been presented for potential application like helical magnetic properties as in FeGe.Öğe Reduction of shunt current in buffer-free IrMn based spin-valve structures(Journal of Magnetism and Magnetic Materials, 2018-06-15) Kocaman, Bayram; Akdoğan, NumanThe presence of thick buffer layers in magnetic sensor devices decreases sensor sensitivity due to shunt currents. With this motivation, we produced IrMn-based spin-valve multilayers without using buffer layer. We also studied the effects of post-annealing and IrMn thickness on exchange bias field (HEB) and blocking temperature (TB) of the system. Magnetization measurements indicate that both HEB and TB values are significantly enhanced with post-annealing of IrMn layer. In addition, we report that IrMn thickness of the system strongly influences the magnetization and transport characteristics of the spin-valve structures. We found that the minimum thickness of IrMn layer is 6?nm in order to achieve the lowest shunt current and high blocking temperature (>300?K). We also investigated the training of exchange bias to check the long-term durability of IrMn-based spin-valve structures for device applications.Öğe Synthesis and characterization of Mn and Co codoped ZnO nanoparticles(Superlattices and Microstructures, 2015-07-01) Abdullahi, Sabiu Said; Köseoğlu, Yüksel; Güner, Sadık; kazan, sinan; Kocaman, Bayram; Ndikilar, Chifu E.MnxCo0.1Zn0.9-xO nanoparticles with different doping concentration (x = 0.0, 0.05, 0.1, 0.15, and 0.2) has been successfully synthesized by microwave assisted combustion synthesis method using urea as a fuel. The structural, morphological, compositional, magnetic and optical properties of these nanoparticles were investigated by X-ray diffraction (XRD), Scanning electron microscopes (FE-SEM JEOL-7001), Energy-dispersive X-ray spectroscopy (EDX), Quantum Design Physical Property Measurement System (PPMS) and UV–visible spectroscopy, respectively. The structural properties showed the formation of single phase Wurtzite structure of ZnO, with the strong diffraction peaks appear in (1 0 0), (0 0 2) and (1 0 1) respectively. The average size of the nanoparticles decreases from 32.65 to 23.69 nm as dopant concentration is increase. Scanning electron microscope (SEM) pictures showed that smaller crystallites have sizes smaller than 100 nm, no phase separation and agglomeration was observed. Moreover, Energy-dispersive X-ray spectroscopy (EDX) confirmed the synthesis results. The magnetic characterization of the samples reveals that the samples showed paramagnetic and ferromagnetic behavior, meanwhile there is no linear variation of magnetic moment with concentration of Mn ion whereby at x = 0.15 the samples show room temperature ferromagnetic behavior with coercive field and remanent magnetization of 47.70 Oe and 1.8 × 10-1 emu/g, respectively. UV–vis spectroscopy results show that the optical band gap of the nanoparticles varies between 3.24 eV and 3.02 eV.Öğe Tailoring magnetic properties by tuning the interface in a Pt/Co/Pt/IrMn system with perpendicular and double-exchange biases(Iop Publishing Ltd, 2022) Kocaman, BayramWe prepared Pt/Co/Pt(t (Pt))/IrMn heterostructures with perpendicular exchange bias (PEB) by inserting a Pt spacer between Co and IrMn. X-ray diffraction demonstrates that the IrMn and Pt layers exhibit a (111) texture promoting PEB. Here, the samples for various Pt spacer thicknesses exhibit double-shifted hysteresis loops with the coexistence of positive and negative exchange biases (EBs). Magnetic force microscopy measurement indicates that this behavior in the as-grown state results from the formation of an antiferromagnetic bidomain state with opposite signs. Also, the magnetic loop behaviors can be tailored by tuning the EB, coercive and switching fields which are sensitive to sub-nanometer changes in the spacer layer (Pt) thickness. It is found that the optimum thickness of the Pt layer is 0.8 nm by considering a well-defined single remanence state, where H (EB) is about seven times as large as the coercivity. Our results indicate that large EB and rather small coercivity necessary for the single-remanence state in the double-shifted Pt/Co/Pt/IrMn systems can be achieved by tuning the interface at atomic level. Moreover, magnetic properties were analyzed in detail depending on Pt space spacer layer thickness between Co and IrMn layers. These results may be useful for potential applications in future multilevel memory devices.Öğe Tek-eksenli Manyetik Anizotropiye Sahip Permalloy (Ni79Fe21) İnce Filmlerin Manyetik ve Yapısal Karakterizasyonu(2022) Kocaman, BayramBu çalışmada, Si(100)/SiO2(~200 nm) alttaş üzerine 4 - 20 nm arasında değişen kalınlıklarda büyütülen permalloy ince filmlerin yapısal ve manyetik özellikleri araştırılmıştır. Permalloy ince filmler eğik açılı magnetron saçtırma tekniği kullanılarak yüksek vakumlu odada hazırlandı. X-ışını foto-elektron spektroskopisi ölçüm sonuçlarından, permalloyun alaşım komposizyonu oranı %21 Fe ve %79 Ni olarak bulundu. X-ışını kırınım ve yansıma ölçümleri, permalloy filmlerinin (111) yönünde, düşük yüzey pürüzlülüğüne sahip ve nominal kalınlıklarda büyüdüğünü gösterdi. Elde edilen ince filmlerin manyetik özellikleri ferromanyetik rezonans (FMR) ve titreşimli örnek manyetometresi (VSM) teknikleri kullanılarak araştırıldı. Film hazırlamada kullanılan eğik biriktirme nedeniyle, filmlerde düzlem içi tek-eksenli manyetik anizotropi gözlemlendi. Mıknatıslanma yönüne göre serbest enerji minimizasyonu yöntemini kullanan bir bilgisayar kodu yazılarak deneysel FMR verileri simule edildi ve bu sayede filmlerin tek eksenli anizotropi sabitleri belirlendi. Ayrıca, zorlayıcı alan ve anizotropi alanı gibi manyetik özelliklerin kalınlığa bağlı olarak değişimleri tartışıldı.
