Browsing by Author "Ou, M. N."

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Anisotropic Magnetism and Magnetoresistance in Iron Nanowire Arrays
(2009-12-01)
Ou, M. N.
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Yang, T. J.
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Chen, Y. Y.
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電子物理學系
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Department of Electrophysics
Highly ordered ferromagnetic iron nanowire (Fe NW) arrays with diameters of about 60 nm and 200 nm were fabricated by electro-chemical deposition into anodic aluminum oxide (AAO) templates. The magnetization measurements show the 60 nm NWs as having a larger anisotropic magnetization. This result was illustrated by the magnetic easy axis and preferred crystal orientation of [110] along with the longitudinal direction of the NWs, revealed by the X-ray diffraction (XRD) patterns. The obtained quadratic magnetic field dependence of the normalized magnetoresistance (MR) at low field for both 60 and 200 nm NWs is attributed to the anisotropic magnetoresistance in low-dimensional systems. Furthermore, the enhanced AIR, observed in the 60 nm NWs is attributed to additional spin-diffusion mechanisms.
Electrical and thermal transport in single nickel nanowire
(2008-02-11)
Ou, M. N.
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Yang, T. J.
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Harutyunyan, S. R.
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Chen, Y. Y.
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Chen, C. D.
The thermal conductivity and electrical resistivity of a suspended nickel nanowire have been measured for T=15-300 K. The temperature dependence of the thermal conductivity and the Lorenz number strongly differ from the bulk. The comparison of the transports in the Ni nanowire shows, that at temperatures 75 < T < 300 K Wiedemann-Franz (WF) law holds, whereas at temperatures T < 75 K the WF law is violated, indicating that thermal current in this material is suppressed more than electrical current. The results are explained by combined effect of confined dimension, enhanced disorder, and grown contribution of N-processes. (C) 2008 American Institute of Physics.
Kondo interactions and magnetic correlations in CePt2 nanocrystals
(2007-04-13)
Chen, Y. Y.
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Huang, P. H.
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Ou, M. N.
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Wang, C. R.
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Yao, Y. D.
The evolution of the Kondo effect and antiferromagnetic (AF) correlations with size reduction in CePt2 nanoparticles (3.1-26 nm) is studied by analysis of the temperature-dependent specific heat and magnetic susceptibility. The AF correlations diminish with size reduction. The Kondo effect predominates at small particle size with trivalent, small Kondo temperature (T-K) magnetic regions coexisting with strongly mixed-valent, large T-K nonmagnetic regions. We discuss the role of structural disorder, background density of states and the electronic quantum size effect on the results.
Superconducting transition parameters in aluminum-lithium alloys (0-10 at.% Li)
(2007-05-01)
Ou, M. N.
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Yang, T. J.
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Chen, B. J.
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Chen, Y. Y.
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Ho, J. C.
The superconducting transition temperatures T-C of face-centered cubic Al1-x-Li-x alloys (x = 0-0.10) exhibit a minimum near x = 0.03 (3 at.% Li). The McMillan strong-coupling T, equation yields a similar trend of the electron-phonon coupling constant.. Meanwhile, the density of states at the Fermi level N(0) decreases monotonically with increasing x. It appears that T-C drops initially due to a reduced N(0), which is then overtaken by alloying-enhanced factors of phonon or electron-phonon interaction. (c) 2007 Elsevier Ltd. All rights reserved.
Thermal and electrical transport properties of a single nickel nanowire
(2007-12-01)
Ou, M. N.
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Harutyunyan, S. R.
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Lai, S. J.
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Chen, C. D.
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Yang, T. J.
The thermal conductivity (K), specific heat (C-p) and the resistivity (p) of a single nickel nanowire have been measured in the temperature range from 4 to 300 K by means of the "self heating 3 omega" technique. Starting with a 100 nm nickel film grown on a Si/Si3N4 substrate by thermal evaporation, a suspended nickel nanowire was then fabricated through e-beam lithography and etching processes. The width and length of the wire were determined by scanning electron microscope (SEM) as 180 nm and 35 mu m respectively. At 300 K the thermal conductivity of nanowire is similar to 20% of the bulk, it diminishes to lower value as temperature decreases. The consequence is opposite to that of the bulk and might be explained by the ristriction of mean free paths of electron/phonon-phonon interactions due to the grain boundaries. An enhancement of specific heat similar to 250% of the bulk is also observed. In addition, the resistivity of nanowire at room temperature is about four times larger than that of the bulk. The small relative resistiv-ity ratio (RRR) confirms the polycrystalline characteristic ofthe nanowire.