Journal of Physics D-Applied Physics
A large magnetoresistance (MR) is observed in a double helical CoMnSi compound over the entire temperature region from 5 K to the maximum measuring temperature of 380 K, with the largest MR ratio of -18.3% at 245 K and the smallest MR ratio of -5.5% at 85 K at 5 T. This phenomenon is ascribed to two different mechanisms in different temperature regions. The suppressed spin fluctuations of the double helical structure are responsible for the MR below 110 K. However, in consideration of the natural multilayer superstructure of CoMnSi, the larger MR above 110 K is ascribed to the decrease in K-space restrictions when the change in magnetic structure from double helical order to fan order occurs.
关键词:
giant magnetoresistance;magnetic-structure;crystal;metals
Physics Letters A
Except for a Peierls transition at T(p) = 180 K, a new transition around T = 270 K in K0.3MoO3 single crystals has been found as evidenced by the anomalies in electrical, magnetic and thermodynamic properties. This transition may be caused by the variation of carrier characteristics or of the charge transfer between cations and anions.
关键词:
Journal of Physics and Chemistry of Solids
Two different potential models to the molecular dynamics (MD) simulations have been applied to investigate the thermoelastic parameter alpha K-T of sodium chloride (NaCl) under high pressure and high temperature. The first one is the shell model (SM) potential that due to the short-range interaction when pairs of ions are moved together as is the case in that polarization of a crystal due to the motion of the positive and negative ions, and the second one is the two-body rigid-ion Born-Mayer-Huggins-Fumi-Tosi (BMHFT) potential with full treatment of long-range Coulomb forces. Particular attention is paid to the comparison of the SM- and BMHFT-MD simulations with the Debye model for the first time, and this model combines with ab initio calculations within local density approximation (LDA) and generalized gradient approximation (GGA) using ultrasoft pseudopotentials and a plane-wave basis in the framework of density functional theory (DFT), and it takes into account the phononic effects within the quasi-harmonic approximation. Note that the MD calculated volumes using SM model is somewhat larger than both the DFT and experimental volumes despite not considering the temperature effect. Compared with SM potential, the MD simulated 300 K isotherm of NaCl with BMHFT potential is very successful in reproducing accurately the measured volumes and the GGA calculated volumes. Generally, it is found that there exist minor differences between the LDA and GGA computed the thermoelastic parameter alpha K-T of NaCI, with both average results giving good agreement with SM-MD simulations. At an extended pressure and temperature ranges, the variation of thermoelastic parameter alpha K-T which play a central role in the formulation of approximate equations of state has also been predicted. The properties of NaCl are summarized in the pressure range of 0-300 kbar and the temperature up to 2000 K. (C) 2012 Elsevier Ltd. All rights reserved.
关键词:
Inorganic compounds;ab initio calculations;High pressure;Thermodynamic properties;molecular-dynamics simulation;density-functional theory;equation-of-state;alkali-halides;thermodynamic properties;elevated-temperatures;thermal expansivity;bulk modulus;ionic solids;nacl
B.H. Kim N.H. Kang W.T. Oh C.H. Kim J.H. Kim Y.S. Kim Y.H. Park
材料科学技术（英文）
For Al 6k21-T4 overlap weld joint, the shear-tensile strength by using the weaving laser was improved as compared to the case of linear laser. For the specimen of low strength, the porosity was distributed continuously along the intersection between the plates and fusion line. However, for the optimized welding condition, large oval-shaped porosities were located only in the advancing track of the concave part. Therefore, the continuity of cracks and porosities played a key role to determine the strength. And, the weaving width was also the important parameter to control the strength. Furthermore, the concave part had more significant hot and cold cracking in the weld and heat-affected zone (HAZ), respectively, than the convex part.
关键词:
Weaving laser
,
Weld microstructure
,
Void
,
Al alloy
B.H. Kim N.H. Kang W.T. Oh C.H. Kim J.H. Kim Y.S. Kim Y.H. Park
材料科学技术（英文）
For Al 6k21-T4 overlap weld joint, the shear-tensile strength by using the weaving laser was improved as compared to the case of linear laser. For the specimen of low strength, the porosity was distributed continuously along the intersection between the plates and fusion line. However, for the optimized welding condition, large oval-shaped porosities were located only in the advancing track of the concave part. Therefore, the continuity of cracks and porosities played a key role to determine the strength. And, the weaving width was also the important parameter to control the strength. Furthermore, the concave part had more significant hot and cold cracking in the weld and heat-affected zone (HAZ), respectively, than the convex part.
关键词:
Weaving laser
,
Weld microstructure
,
Void
,
Al alloy
Physica C-Superconductivity and Its Applications
Superconducting cuprate fluorides Nd0.7Sr1.3Cu(O,F)(4-delta) with T-c = 44 K were obtained by solid phase fluorination of the T-structure Nd0.7Sr1.3CuO4-gamma at low temperature (200-300 degrees C) using CuF2 as fluorinating reagent. The oxyfluoride has K2NiF4 structure with S.G. I4/mmm as its precursors, but the evident lattice expansions were observed. The a-axis expands from 3.7257(2) Angstrom to 3.9288(5) Angstrom and c-axis from 12.8240(3) Angstrom to 12.9630(2) Angstrom. No trace of SrF2 was detected in these fluorinated products. XRD and magnetic measurement revealed that the superconductivity in the fluorinated products originated from the oxyfluorides with reduced CuO2 plane and in the presence of the apical anion.
关键词:
hole concentration;copper;route;a=ca;tc
