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    Comparing Different Approaches to Form Cobalt Oxide Layer on CoPt Nanoparticles
    (Adiyaman University, 2020) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet
    We 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.
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    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, Ahmet
    Pd-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.
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    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, Ahmet
    We 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.
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    Effect of Gd-doping in Ni/NiO core/shell magnetic nanoparticles (MNPs) on structural, magnetic, and hydrogen evolution reaction
    (Aip Publishing, 2022) Adanur, Idris; Karazehir, Tolga; Dogru Mert, Basak; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, Gd-x-doped Ni/NiO MNPs (x: 0.0%, 2.5%, 5.0%, and 10.0%) with a protective polyvinylpyrrolidone (PVP) layer have been synthesized via a polyol reduction process. The x-ray diffraction patterns revealed that samples have a cubic structure with Fm3m space group and no change in the crystallite structure was observed with doping Gd3+ ions. The crystallite size (D-c) decreases from 2.70 to 1.27 nm when Gd is doped into Ni/NiO MNPs. Transmission electron microscopy analysis revealed that the Ni/NiO MNPs with Gd(5%) concentration are formed as spherical multicore-like shape core/shell MNPs with a protective PVP layer. The magnetic hysteresis measurements taken at 10 and 300 K show that the saturation magnetization (M-s) decreases with increasing Gd3+ ions in the structure. The highest effective magnetic moment (mu(eff)) was obtained as 10.34 mu(B) in the NG-2 sample. We ascribe that the high mu(eff) value in this sample is due to the increase in d-f exchange interaction between Ni(3d(7)) and Gd(4f(7)) and the contribution of the dipole moment of PVP molecules. The electrochemical measurements showed that the current density values were 0.294 and 0.319 mA/cm(2) at-1.3 V in the absence of Gd (NG-0) and Gd(5%) doped (NG-2) samples, respectively. beta c was 159 and 132 mV/dec for NG-0 and NG-2 samples, respectively. The diminishing of beta c and the charge resistance (Rct) proved that the Gd doped catalyst enhanced the hydrogen evolution activity and the Gd(5%) doped sample exhibited the highest catalyst performance.
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    Effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles
    (Taylor & Francis Ltd, 2018) Adanur, Idris; Akyol, Mustafa; Ekicibil, Ahmet
    We report the effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles (MNPs) synthesised by the polyol process. The samples in this work were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The XRD results indicate that samples synthesised by EG-NaOH and 1.2H-OAm/OAc have a cubic structure with space group Fm-m. The average crystallite sizes of these samples are found to be approximate to 20.7 and 16.2nm, respectively. The sample synthesised by a combination of EG-OAm/OAc grows in nanorod form, whereas that synthesised by EG-NaOH and 1.2H-OAm/OAc has a spherical shape. The temperature dependence of the magnetisation, (M-T) measurements, indicate that the EG-NaOH sample has a superparamagnetic transition, while the 1.2H-OAm/OAc sample shows ferromagnetic behaviour in the temperature range of 5-380K. The magnetic anisotropy constants of the EG-NaOH and 1.2H-OAm/OAc samples extracted from the M-T experiments, are 141.3x10(5) and 10.5x10(5)erg/cm(3), respectively. In addition, the magnetic hysteresis measurements taken at 5 and 300K show that the 1.2H-OAm/OAc sample is more stable than the sample synthesised by EG-NaOH. The overall results are important for the use of the Ni MNPs for low- and room-temperature applications in bio- and nano-technology.
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    Evaluation of nanoparticle formation and magnetic properties by boron doping in Ni/NiO? nanoparticles
    (Springer, 2020) Adanur, Idris; Akyol, Mustafa; Tezcan, Fatih; Kardas, Gulfeza; Ekicibil, Ahmet
    In this work, Boron-doped B-x:Ni/NiO delta [x(%) = 0.0, 5.0, 10.0 and 15.0] core/shell magnetic nanoparticles were synthesized by the polyol reduction process. The XRD spectra of the samples indicate that the B addition does not cause any change in the cubic structure of Ni. The TEM photographs present that nanoparticle formation and accumulation orientation occurs in various shapes as spherical, octahedral-like and octopus-like accumulation. The average particle sizes of B-x:Ni/NiO(delta)MNPs forx(%) = 0.0, 5.0, 10.0, 15.0 were found as similar to 90, 12, 46, 5 nm, respectively, from the TEM images. It is observed from the temperature and magnetic field dependence magnetization measurements that magnetization of Ni/NiO delta core/shell MNPs increases with increasing Boron concentration from 5 to 15%. One can be deduced that this increment in the magnetization comes from the resulting of strengthening the Ni-B ferromagnetic interaction. The highest saturation magnetizations under 1 T magnetic field were found as similar to 37 and similar to 30 emu/g at 10 and 300 K, respectively.
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    Magnetic field dependence of magnetic coupling in CoCr2O4 nanoparticles
    (Elsevier, 2017) Akyol, Mustafa; Adanur, Idris; Ayas, Ali Osman; Ekicibil, Ahmet
    CoCr2O4 spinel nanoparticles synthesized by sol-gel method have been worked extensively by performing structural and magnetic characterization techniques, as well as modeling the experimental results. The microstructure analysis shows that the crystallite size of CoCr2O4 nanoparticles, which are purely crystallized in cubic phase with space group Fd3m, is similar to 75 nm. The grain size distribution determined from scanning electron microscope images indicates that the particles are uniformly formed and distributed homogenously in the structure. A comprehensive magnetic study has been performed by measuring magnetic moment as a function of temperature and external magnetic field. The paramagnetic to ferromagnetic phase transition and non-collinear spiral magnetic transition have been observed in CoCr2O4 nanoparticles at 96 and 27 K, respectively. Interestingly, we observed field-condition shift in lock-in transition which is found as 16 and 8 K for FH and FC, respectively. The exchange bias effect is observed when the CoCr2O4 sample is cooled under magnetic field. The magnitude of exchange bias field decreases with increasing temperature from 5 to 50 K, and it is vanished above 50 K. In addition, we also worked on the magnetic entropy change around the paramagnetic to ferromagnetic phase transition. The magnetic entropy change is found as -0.87 J/kg K under 6 T magnetic field.
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    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, Faruk
    Developing 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.
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    Synthesis of monodisperse CoPt nanoparticles: Structural and magnetic properties
    (Elsevier, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet
    We 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.