Browsing by Author "Wu, MK"

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Characterization of lead-bismuth eutectic nanowires
(2005-04-01)
Kuo, CG
;
Hsu, YY
;
Wu, MK
;
Chao, CG
;
材料科學與工程學系
In this work, lead-bismuth eutectic alloy nanowires were fabricated by a novel vacuum melting method and centrifugal process. An anodic aluminum oxide (AAO) template was used to produce an array of ordered, dense, and continuous Pb-Bi nanowires. Scanning electron microscopy and transmission electron microscopy investigations reveal that nanowires with a diameter of 80 nm are composed of Pb7Bi3 and Bi phases, and have a single orientation of growth. Magnetic susceptibility and hysteresis measurements have been used to characterize the superconductive and magnetic properties of the nanowires. The results show that Pb-Bi nanowires have a slightly lower superconducting transition temperature than Pb-Bi eutectic alloy bulk, and only about 1% superconductivity volume fraction in magnetic fields both perpendicular and parallel to the plate. In magnetization curves, a fairly large hysteresis is observed for both field orientations.
Magnetic field dependence of low-temperature specific heat of the spinel oxide superconductor LiTi2O4
(2004-08-01)
Sun, CP
;
Lin, JY
;
Mollah, S
;
Ho, PL
;
Yang, HD
Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi2O4 has been elaborately investigated. In the normal state, the obtained electronic coefficient of specific heat gamma(n)=19.15 mJ/mol K-2, the Debye temperature Theta(D)=657 K and some other parameters are compared with those reported earlier. The superconducting transition at T(c)similar to11.4 K is very sharp (DeltaT(c)similar to0.3 K) and the estimated deltaC/gamma(n)T(c) is similar to1.78. In the superconducting state, the best fit of data leads to the electronic specific heat C-es/gamma(n)T(c)=9.87 exp(-1.58 T-c/T) without field and gamma(H)proportional toH(0.95) with fields. In addition, H-c2(0)similar to11.7 T, H-c(0)similar to0.32 T, xi(GL)(0)similar to55 A, lambda(GL)(0)similar to1600 Angstrom, and H-c1(0)similar to26 mT are estimated from the Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All results from the present study indicate that LiTi2O4 can be well described by a typical type-II, BCS-like, moderate coupling, and fully gapped superconductor in the dirty limit. It is further suggested that LiTi2O4 is a moderately electron-electron correlated system.
Raman scattering studies of single-crystal La1-xSrxMnO3
(2005-06-01)
Her, JL
;
Liu, HL
;
Mukovskii, YM
;
Lin, JY
;
Hsu, YY
We present the results of Raman scattering studies of single-crystal La1-xSrxMnO3 (x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.35) as a function of doping and in the temperature range 10-300 K. The room-temperature Raman spectrum of the x = 0.05 compound displays four phonon bands near similar to 260, 488, 612, and 674 cm(-1). With increasing Sr doping, and a corresponding structural phase transition from an orthorombic to a rhombohedral form, there is a broadening of the linewidths and a decrease in intensities of these phonon modes. 14 When the temperature is lowered, for the x = 0.05 material, two low-frequency phonons associated with the out-of-phase rotation and internal bending of MnO6 octahedra show a noticeable hardening below the canted anti-ferromagnetic transition, which is an evidence for strong spin-phonon coupling. Interestingly, this anomalous behavior disappears in the higher Sr doping level.