Browsing by Author "Wang, CR"

Now showing 1 - 2 of 2

Electronic transport in insulating AlPdRe quasicrystals
(2004-02-18)
Rosenbaum, R
;
Murphy, T
;
Brandt, B
;
Wang, CR
;
Zhong, YL
Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range 300 K greater than or equal to T greater than or equal to 50 K, the resistivities follow a simple inverse temperature law: rho(T) rho(0)/T(1.0+/-0.1). Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where rho(T) = rho0/T-0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as T --> 0 K. These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range 0.18 less than or equal to y less than or equal to 0.43. The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.
Temperature dependence of magnetic properties in Ni-Mn-Ga shape memory alloys
(2004)
Lee, MD
;
Nong, NV
;
Thuy, NP
;
Yao, YD
;
Lee, SF
Due to exhibiting giant field-induce strain, the Ni2MnGa shape memory alloys are great interest for both scientific researches and industry applications. The non-stoichiometric Ni50Mn25+xGa25-x alloys with x varied from 1.5, 2.5 to 4 have been fabricated by arc-melting. Martensitic transformation temperature for structure transformation from tetragonal to cubic (T-M) was observed from the magnetization, electrical resistivity and X-ray diffraction studies as functions of temperature below 400 K. We found that T-M increases roughly from 280 K to 310K with increasing x from 1.5 to 4. However, the Curie transition (T-M) is roughly at 380 K for all the samples, it is insensitive to the variation of Mn/Ga ratio. The electrical resistivity data exhibit a deep near T-M and a slope change near T-C. We have experimentally demonstrated that the shape memory effect can be occurred at room temperature with a proper concentration variation of Mn and Ga. (C) 2004 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.