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Öğe Comparing Different Approaches to Form Cobalt Oxide Layer on CoPt Nanoparticles(Adiyaman University, 2020) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetWe have studied the effect of preparation methods, under argon gas and in the air environment, on the cobalt oxide formation of CoPt nanoparticles by the polyol process. The formation of cobalt oxide for both samples was investigated by the x-ray diffraction (XRD) method and cobalt oxide peaks are observed in the air prepared sample. Rietveld refinement analyses revealed that all samples exhibit a chemically distorted cubic crystal structure. The average particle size was determined <8 nm by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) was revealed the chemical compositions with possible oxygen formation in the structure. The blocking temperature is reduced to 28 K in the air prepared sample due to cobalt oxide formation. The hysteresis gap disappeared above the blocking temperature and no saturation is observed up to ±5 T external field due to the system switching from ferromagnetic state to paramagnetic state. Similarly, the coercive field was decreased from 1021 Oe to zero with increasing the temperature from 5 K to 300 K. The formations of the cobalt oxide layer did not interact with CoPt nanoparticles, therefore, the maximum exchange bias was observed about 93 Oe at 5 K. © 2020, Adiyaman University. All rights reserved.Öğe Detailed investigation of structural and magnetic properties of multiphase binary Pd-Co alloys prepared by modified polyol process(Elsevier Science Sa, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetPd-Co based magnetic alloy nanoparticles were prepared by the modified polyol process and stabilized by polyvinylpyrrolidone (PVP) and 3-aminopropyl-trimethoxysilane (APES) capping agents and further reduction of metal salts with Sodium borohydride (NaBH4) at high temperature to form desired NPs. We have a detailed investigation of the effect of Pd concentration in the Pd-Co alloy NPs on structural and magnetic properties. XRD and Rietveld refinement analyses were confirmed that the multiphase structures of fcc-PdCo, fcc-Co, and hcp-Co phases coexist at low Pd loading samples. Over %50 of Pd loading resulted in a single fcc-PdCo phase with reduced lattice parameter to 4.0079 angstrom and d((111))-space to 2.31 angstrom. TEM and SEM images reveal well dispersed and uniformly distributed NPs with an average particle sizes of below 7 nm. The elemental compositions and the characteristic OH, CH, CO stretching peaks of capping agents were confirmed by EDS and FT-IR spectrums, respectively. M(T) and M(H) curves revealed that there are multi magnetic phase transitions in the Pd-Co structure as a function of Pd loading from superparamagnetic to ferromagnetic phase or back to superparamagnetic phase by reducing the temperature from 300 K to 5 K. We observed that the blocking temperature (T-B) could not be detected due to 5% Pd loading below 300 K, while it reduced up to 55 K at high Pd loading of 62%. The coercive field (H-c) was increased to similar to 1900 Oe for Pd0.62Co0.38 sample due to the smallest particle size as 5.26 nm. The highest amount of Co resulted in maximum saturation magnetization (M-s) up to 65.5 emu/g for 5% Pd concentration. We measured the M-r/M-s ratios were less than 0.5, which is due to the internal stress that results in the uniaxial magnetic anisotropy in the structure. The maximum K-eff and mu(f.u). values were found to be over 12.9 x 10(6) erg/cm(3) and 0.72 mu(B) at 5 K for 5% Pd concentration, respectively. (C) 2021 Elsevier B.V. All rights reserved.Öğe Effect of Ag-doping process into the yttrium iron garnet (Y3Fe5O12) thin films on the structural, magnetic and optical properties(Springer, 2024) Demiryurek, Nazan; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetIn this work, the effect of Ag doping process (directly and as a nanoparticle) into the Y3Fe5O12 (YIG) thin films on the structural, morphological, optical and magnetic properties was studied in detail. Ag-doped YIG thin films were grown on thermally oxidized Si substrates by following sol-gel and spin-coating methods. All films were crystallized without cracks by two-stages heat treatment process. The XRD patterns confirm the formation of YIG peaks, and metallic Ag peaks which settled into the structure without bonding with the YIG components. In both Ag doping processes, the coercive field (H-c) and saturation magnetization (M-s) values of the samples containing 3% Ag are significantly lower than the other samples. The M-s values of 5% Ag doped samples were found the highest in both series. The M-s values of the films between in-plane and out-of-plane measurement increased with the Ag concentration. The optical measurements indicate an absorption peak in the range of 0-4 eV in both sample series and the optical band gap of the films decreased with the Ag doping due to its metallic characteristic. The ferromagnetic resonance measurements indicate that the lowest FMR linewidth as 92 Oe is seen in the 1% Ag-doped YIG sample. The relatively cheap and easy production of the used method and additive material may enable the widespread the usage of Ag-doped YIG thin films in magneto-optical devices.Öğe Effect of boron content on structure and magnetic properties in CoFe2O4 spinel nanocrystals(Elsevier Science Sa, 2018) Akyol, Mustafa; Adanur, Idris; Ayas, Ali Osman; Karadag, Faruk; Ekicibil, AhmetWe study the effect of boron content on the structural and magnetic properties of CoFe2O4 spinel nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites in spinel lattice. The crystallite sizes of samples are found in a range of 47-67 nm that is in the limit of single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not seen in the temperature range of 5-400 K. The magnetic domains are pinned with adding boron ions into the CoFe2O4 spinel structure at low temperatures. Thus, an increment in the propagation field (H-p) and temperature (T-p) by boron content in CoFe2O4 structure is observed. In addition, the saturation magnetization (M-s) normalized by crystal size increases with increasing boron concentration. The temperature dependence of magnetic properties of the samples taken by experimental data are confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites. (C) 2018 Elsevier B.V. All rights reserved.Öğe Investigation of Magnetic Anisotropy in the Ni-Ge and Ni(NiO)-Ge Thin Films(Elsevier, 2021) Kaya, Dogan; Akyol, Mustafa; Wang, Yitao; Guo, Quanmin; Karadag, Faruk; Ekicibil, AhmetWe studied the structural and magnetic properties of Ni-Ge and Ni(NiO)-Ge films deposited by physical vapor deposition technique on the Si/SiO2 substrate. The x-ray diffraction (XRD) analysis show that as-prepared samples exhibit clear peaks of Ge, Ni, and Au with a cubic symmetry belongs to space group Fm (3) over barm. Due to the thermal annealing process at 350 degrees C, NiO layer formed on Ni layer. The NiO formation has reduced the interaction of Ni-Ge interlayer which is confirmed by XRD data. Investigation of temperature-dependent magnetic moment revealed the Neel and the critical temperatures as 93 and 294 K, respectively. The hysteresis loops showed that the preferred magnetization direction for samples at 300 K is the in-plane (parallel) which reaches saturation easier than out-of-plane (perpendicular) loops. The formation of NiGe interlayer resulted in a magnetically dead-region which led to decrease ferromagnetic domain and the coercive field. (C) 2020 Elsevier B.V. All rights reserved.Öğe Magnetically separable low Pt substituted Co nanoparticles: Investigation of structural, magnetic, and catalytic properties(Elsevier, 2022) Kaya, Dogan; Isik, Hasan Huseyin; Isik, Ilknur Baldan; Adanur, Idris; Wang, Yitao; Akyol, Mustafa; Karadag, FarukDeveloping multifunctional nanoparticles (NPs) for magnetic and catalytic purposes is crucial for controlling magnetic properties and reducing production costs. We synthesized Co and low Pt loaded CoPt NPs by the modified polyol process. Co and CoPt NPs exhibited coexist fcc and hcp phases which are confirmed with x-ray diffraction and Rietveld refinement analysis. Scanning electron microscopy images revealed the average size of the NPs smaller than 9 nm with a narrow distribution. An irreversible magnetization-temperature behavior of the particles is observed in the modes of zero-field cooled and field cooled with a strong ferromagnetic signal close to 350 K. The field-dependent magnetization up to +/- 5 T was investigated to determine coercive field (H-c), exchange bias (H-E), saturation magnetization (M-s), remanent magnetization (M-r), and the ratio of remanent magnetization to saturation magnetization (M-r/M-s). There is a general decrease in magnetic values due to an increase of both the temperature and the Pt ratio in Co nanoparticles. When the Pt/Co ratio drops to 1%, the sample was measured with the highest H-c value of 648.5 Oe and M-s value of 100 emu/g at 5 K. On the contrary, increasing the concentration of Pt to 10% resulted in a reduction for the M-s value below 40 emu/g. Besides, cyclic voltammetry measurements showed apparent hydrogen reduction in the potential range of -0.91 V and -0.96 V (vs Ag/AgCl) and 10% Pt loaded CoPt NPs exhibits the highest activity after 10th cycles and increase the activity up to 15.80 mA cm(-2) at -1.2 V due to the surfactant.Öğe Optical properties of NiO films: Effect of nitrogen-doping, substrate temperature and band gap estimation using machine learning(Elsevier Ltd, 2024) Kaya, Dogan; Hopoğlu, Hicret; Çelik, Ali; Akyol, Mustafa; Karadag, Faruk; Şenadım Tüzemen, Ebru; Ekicibil, AhmetIn this study, nickel oxide (NiO) thin films were synthesized on glass substrates using RF magnetron sputtering with varying nitrogen (N) doping ratio and substrate temperatures to explore modifications in their structural, morphological, and optical properties. The films were prepared using a high-purity NiO target under controlled sputtering conditions. Structural analysis by X-ray diffraction revealed an improvement in crystallinity in the (2 0 0) direction with increasing N ratio. In contrast, higher N ratio led to the suppression of (1 1 1) and (2 2 0) peaks, indicating a significant influence of N on the crystal structure and orientation. The films’ thickness and morphology, examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, showed uniform and homogeneous growth with smooth surface topologies. Optical properties, assessed by UV–Vis-NIR spectrophotometry, demonstrated a decrease in transmittance and a redshift in the absorption edge with increased N doping, corresponding to a narrowing of the energy bandgap from 3.7 eV to 3.45 eV. This bandgap reduction is attributed to N incorporation substituting oxygen sites, introducing defect states within the band structure. Additionally, the impact of substrate temperature on film growth enhanced crystallinity and orientation along the (1 1 1) plane at higher temperatures, with a simultaneous reduction in film thickness due to increased adatom mobility and potential thermal decomposition. The evaluation of Kernel Ridge Regression (KRR) and Ridge Regression (RR) models revealed their effectiveness in predicting band gap values for thin films at varying substrate temperatures and thicknesses. While RR excelled in predicting a band gap of 3.6 eV for a film with a substrate temperature of 24 °C and a thickness of 112.7 nm, KRR outperformed in predicting a band gap of 3.65 eV for a film with a substrate temperature of 24 °C and a thickness of 107 nm. These findings elucidate the dual influence of N doping and substrate temperature on enhancing the functional properties of NiO thin films, promising for applications in optoelectronic devices and gas sensors. © 2024 Elsevier B.V.Öğe Self-Defined Transition State in Hybrid C70-Au Clusters Created by the Scanning Tunneling Microscope Tip(Amer Chemical Soc, 2019) Kaya, Dogan; Wang, Yitao; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet; Guo, QuanminManipulation of C-70-Au hybrid nanoclusters was investigated using a scanning tunneling microscope (STM) tip. We demonstrate that removing a selected C-70 molecule from the cluster by STM-tip resulted in an intermediate transition state without thermal decomposition. The molecule rotates and diffuses around the cluster and leaves the cluster without taking an additional molecule and Au atoms due to the rather weak interaction between molecules and the surface atoms. After removing a C-70 molecule, the van der Waals interaction among the remaining C-70 molecules leads to reorganization of the cluster. This self-transition-state is due to a weak charge transfer between the molecules and the surface. The extraction of molecules in a Reshape Transition Interstate ring cluster resulted in polygonal Au island formation.Öğe Structural, magnetic and optical properties of Au/YIG, YIG/Au and Au/YIG/Au multilayer thin film stacks(Elsevier, 2020) Akyol, Mustafa; Demiryurek, Nazan; Iloglu, Onur; Tumen, Kutluhan Utku; Karadag, Faruk; Ekicibil, AhmetY3Fe5O12 shortly named YIG thin film and various form of Au and YIG thin film stacks have been grown on quartz substrate using both spin-coating and sputtering methods. The films are crystallized in cubic phase after heat treatments process that is optimized to avoid cracks on the surface. The thickness of the YIG layer measured by cross-section electron microscope imaging technique are found as about 80 nm for all samples. While the root-mean-square surface roughness of the YIG film is in sub-nanometer scale, it increases up to 2.86 nm by adding Au layer in the film structure. All films exhibit in-plane easy axis and low coercive field at room temperature. But, the saturation magnetization values of films decrease with Au layer. Whereas the optical transmission value is around 80% for YIG samples above 400 nm, it decreases dramatically with Au in the film stacks. The highest absorption coefficient value is found as similar to 20 x 10(4) cm(-1) in Q/Au/YIG structure. This strong absorption might come from the localized surface plasmon polaritons of Au noble metals in YIG structure because it enhances the electronic transition from crystal field splitting. As a result of these measurements, it is seen that the Au layer reduces the magnetization of the films, while increases the absorption rate significantly. Due to considerably low production cost of YIG in this work, it might open to commonly use of them in the magneto-optical devices.Öğe Synthesis of monodisperse CoPt nanoparticles: Structural and magnetic properties(Elsevier, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetWe have investigated CoPt nanoparticles by the simultaneous reduction of Pt (acac)(2) and Co (acac)(2) with polyol method under N-2 atmosphere. The formation of CoPt nanoparticles requires further study of possible increased Pt concentration and size effects on their structural and magnetic properties. We found that as-synthesized CoPt NPs exhibits a chemically disordered cubic phase in the compositions with an average crystalize size of 4.44 nm confirmed by X-ray diffraction (XRD) method and Rietveld refinement analyses. Uniformly distributed the average cluster size of CoPtx nanoparticles decreased from 13.7 nm to 7.6 nm with decreased Pt concentration from 2.3 to 0.5 which determined by scanning electron microscopy (SEM). Magnetic properties are characterized by vibrating sample magnetometer (VSM) for zero field cooled (ZFC) and field cooled (FC) conditions between 5 and 300 K and applied field up to +/- 5 T. Magnetic results indicate that the Co rich CoPtx nanoparticles exhibit large coercive field up to 1358 Oe at 5 K and this value decrease with increasing temperature and Pt concentration for all samples. Due to a transition from ferromagnetic to a superparamagnetic phase with elevated temperature, coercivity and exchange bias nearly vanished for all samples. (C) 2020 Elsevier B.V. All rights reserved.
