Browsing by Author "Chung, T. Y."

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Design of a Hybrid Multiperiod Robinson Wiggler for TPS Light Source
(2016-06)
Huang, C. W.
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Chung, T. Y.
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Chang, C. H.
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Hwang, C. S.
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電子物理學系
A Robinson wiggler is designed to decrease the emittance within 1 nm . rad for Taiwan Photon Source. According to an analysis of the beam dynamics, decreasing the emittance with a multiperiod Robinson wiggler is more efficient than a single-period traditional Robinson wiggler. This wiggler consists of a dipole field and a strong gradient field, which creates a strong dynamic field integral multipole error. To enhance the gradient field and to have also a small dynamic field integral multipole error, a compensated side-pole design and an edge-pole shape in each pole are proposed in this paper. After optimization of the magnet, the dipole and gradient fields are 0.82 T and -37 T/m, respectively. The concept of the design of the magnetic circuit and the results of an analysis of the magnetic field are discussed herein.
Fabrication and low temperature thermoelectric properties of NaxCoO2 (x=0.68 and 0.75) epitaxial films by the reactive solid-phase epitaxy
(2007-02-05)
Chang, W. J.
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Hsieh, C. C.
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Chung, T. Y.
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Hsu, S. Y.
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Wu, K. H.
The authors have fabricated NaxCoO2 thin films via lateral diffusion of sodium into Co3O4 (111) epitaxial films (reactive solid-phase epitaxy [Ohta , Cryst. Growth Des. 5, 25 (2005)]). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane rho(ab), the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the NaxCoO2 thin films. (c) 2007 American Institute of Physics.
Fabrication and X-ray absorption NaxCoO2 spectroscopy in layered cobaltate thin films
(2007-03-01)
Chang, W. J.
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Lin, J.-Y.
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Chung, T. Y.
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Chen, J. M.
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Hsu, C.-H.
NaxCoO2 (x similar to 0.68) thin films were fabricated on sapphire (0 0 0 1) substrates via the lateral diffusion of sodium into Co3O4 (1 1 1) films, which were grown by pulsed-laser deposition. From the results of X-ray diffraction and in-plane resistivity rho(ab), the single phase and the metallic behaviors of these NaxCoO2 films can be identified. For the same sodium content x, rho(ab) is consistent with that of single crystals. In addition, the O 1s X-ray absorption near edge spectra of thin films are measured and compared with those of single crystals. (c) 2006 Elsevier B.V. All rights reserved.
Magnetic vortex structures probed by magnetotransport in sub-micron permalloy disks
(2010)
Kuo, C. Y.
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Chung, T. Y.
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Hsu, S. Y.
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電子物理學系
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Department of Electrophysics
We have successfully used magneto-transport measurement to study magnetization reversal of domain structure in single sub-micron magnetic disks of various sizes, 300nm <= diameter <= 5 mu m and 36nm <= thickness <= 48nm. The magnetoresistance (MR) resulted from the anisotropic magnetoresistance effect can reveals the magnetization reversal of a single disk as confirmed by the magnetic force microscopic results. For a fixed thickness, the remanent domain state can transits from the multi-domain to vortex states by decreasing the disk diameter. Here, the nucleation and annihilation fields of vortex core are determined from disk's hysteretic MR and analytically described by the micromagnetic LLG calculation incorporated with the "rigid" vortex model developed by Guslienko et al. under the consideration of magnetostatic, exchange, and Zeeman energies
Magneto-transport flipping induced by surface oxidation in Co films
(2009)
Chung, T. Y.
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Hsu, S. Y.
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電子物理學系
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Department of Electrophysics
We have performed low temperature magnetoresistance (MR) and magnetization measurements for a series of thin Co films with different degrees of oxidation to investigate the role of surface oxidation on magnetic properties. For films with less oxidation, magneto-transport exhibits the typical anisotropic magnetoresistance behavior. However, magneto-transport flips completely in films with severe oxidation. The inverse MR is replaced by the normal MR when the applied magnetic field is a long the current. The normal MR is changed to the inverse MR when the applied magnetic field is perpendicular to the current. Since the disorder will enhance the spin-orbital interaction and electron-electron interaction in thin films, we suggest that both mechanisms may be responsible for the flipping in anisotropic MR induced by surface oxidation.
The angular dependence of Neel wall resistance by magnetotransport in the centipedelike Permalloy structures
(2009-04-01)
Chung, T. Y.
;
Hsu, S. Y.
;
電子物理學系
;
Department of Electrophysics
The angular dependence of Neel wall resistance has been studied by measuring the in-plane magnetoresistances (MRs) of the centipedelike Permalloy (Py) structure, which consists of a central wire with numerous orthogonally bisecting finger wires. All Py wires were designed to have a single domain structure at remanence and high anisotropy by the geometric control. The remanent domain at the junction between the central and finger wires is determined by the anisotropy constants of both wires and hence, variable angles of Neel wall can be achieved. Using a simple resistance-in-series model in corporation with the anisotropic MR effect, the analyses of the longitudinal and transverse MRs of the centipedelike structure give the domain wall resistance. Our results show that the Neel wall resistance is about milliohm and decreases with decreasing the relative angle between two domains. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068629]