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Öğe A comparison of the magnetic properties of Ni and Co nanowires deposited in different templates and on different substrates(ELSEVIER SCIENCE BV, 2015) Yalcin, O.; Kartopu, G.; Cetin, H.; Demiray, A. S.; Kazan, S.Nickel (Ni) and cobalt (Co) nanowire arrays (NWs) grown by electrode position in porous nano-templates are studied by the ferromagnetic resonance (FMR) technique at room temperature (RT) by comparing the effects of template type (alumina and polycarbonate) and the deposition substrate (i.e., metallic back contact). The line-width and resonance field of the FMR spectra strongly depends on the orientation of the applied field direction. A model is developed to analyze the spectra in order to extract the magnetic parameters such as g-values, spin-spin relaxation times (T-2) and uniaxial an isotropy parameters. The experimental FMR spectra and their resonance field values were fitted using the imaginary part of magnetic susceptibility and a dispersion relation of magnetization, including the Bloch-Bloembergen type damping term. The easy axes of magnetization for all Ni and Co NWs were found to be perpendicular to the wire-axis. Surface spin modes have been observed only when pure Au was used as substrate. A discussion will be provided to explain the observed differences in terms of the anisotropic behavior and magnetic parameters of the NWs for different substrates and growth templates. (C) 2014 Elsevier B.V. All rights reserved.Öğe Size effects and origin of easy-axis in nickel nanowire arrays(AMER INST PHYSICS, 2011) Kartopu, G.; Yalcin, O.; Choy, K. -L.; Topkaya, R.; Kazan, S.; Aktas, B.High quality compact Ni nanowire (NW) arrays with aspect ratios (wire length/diameter) varying between 70-171 for a wire length of similar to 6 mu m, and between 3-400 for a constant wire diameter of 60 nm were successfully grown by direct current electrodeposition into free standing porous alumina templates having a lattice constant, i.e., interpore distance, of 105 nm. The NWs have been investigated using a combination of scanning-and transmission-electron microscopies, selected-area electron diffraction, x-ray diffraction analysis, ferromagnetic resonance (FMR), and vibration sample magnetometer techniques at room temperature. Microscopic and diffraction results show that the wires are uniform and mostly single-crystalline, being 220-oriented along the growth direction. Magnetic properties of samples are heavily dependent on the wire length as well as the diameter or packing factor, P (the volume fraction of wires/template). The FMR spectra and the field orientation dependence of the resonance field values were fitted using the imaginary part of magnetic susceptibility and a dispersion relation of magnetization, including the Bloch-Bloembergen type damping term. Combined with hysteresis (M-H) results, these indicate that the preferred (easy) axis of magnetization is parallel to the NW-axis for P < 33%. On the other hand, strong interwire exchange interactions are determined to supply a magnetization state with preferred axis perpendicular to the wires for samples with P > 33%. Comparison with relatively thick (110 nm diameter) and loosely packed (P similar to 10%) Ni NW arrays suggest that the magnetization reversal mechanism could be that of curling type. (C) 2011 American Institute of Physics. [doi:10.1063/1.3531565]Öğe Temperature evolution of magnetic properties for (Cu/Co)(60)/Fe multilayer(ELSEVIER SCIENCE BV, 2015) Yalcin, O.; Unluer, S.; Kazan, S.; Ozdemir, M.; Oner, Y.In order to investigate the magnetic properties by ferromagnetic resonance (FMR) techniques, (Cu/Co)(60)/ Fe multilayer on Si(001) substrate has been prepared by conventional sputtering. Evolution of the FMR spectra with temperature, resonance field, and magnetization curve has been calculated using the Lanclau-Lifshitz equation of motion for magnetization with the Bloch-Bloembergen type damping term. An almost linear evolution of frequency of resonance field has been shown for x-, k- and q-band spectra. By the analysis of the resonance field-frequency relation, the effect of the internal field is refined and thus the spectroscopic g-value and internal field were calculated. The magnetostatic signal originated from the magnetostatic anisotropy energy has been determined to be opposed by the decreasing exchange and dipolar energies. (C) 2014 Elsevier B.V. All rights reserved.Öğe The local environment of Cr3+ impurities in normal and x-rays irradiated carbon doped ruby: An electron paramagnetic resonance (EPR) study(ELSEVIER SCIENCE BV, 2015) Kazan, S.; Acikgoz, M.; Yalcin, O.Local environment of substitutional paramagnetic point defect (impurity) in normal and x-ray irradiated commercially available alpha-Al2O3:C samples (commercial product of Landauer, Inc.) has been studied by using the electron paramagnetic resonance (EPR) technique at room temperature. In both samples the EPR spectra showed strongly angular dependent behavior. The zero-field splitting (ZFS) parameters (ZFSPs) have been determined for substitutional Cr3+ centers. The observed additional EPR signals for x-ray irradiated sample were attributed to another center with different spin Hamiltonian (SH) parameters. In addition to the experimental findings, the ZESPs and the local structure of the Cr3+ ions were theoretically determined using superposition model (SPM) calculations. (C) 2014 Elsevier B.V. All rights reserved.
