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    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, Ahmet
    We 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.
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    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, 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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    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, Quanmin
    Manipulation 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.