8,472 research outputs found
Irrigation and drainage performance assessment: practical guidelines
Irrigation management / Drainage / Performance evaluation / Performance indexes / Evapotranspiration / Precipitation / Water balance / Participatory rural appraisal / Databases / Simulation
Persistence of the valence bond glass state in the double perovskites Ba2-xSrxYMoO6
Peer reviewedPublisher PD
Evidence for hard and soft substructures in thermoelectric SnSe
SnSe is a topical thermoelectric material with a low thermal conductivity
which is linked to its unique crystal structure. We use low-temperature heat
capacity measurements to demonstrate the presence of two characteristic
vibrational energy scales in SnSe with Debye temperatures thetaD1 = 345(9) K
and thetaD2 = 154(2) K. These hard and soft substructures are quantitatively
linked to the strong and weak Sn-Se bonds in the crystal structure. The heat
capacity model predicts the temperature evolution of the unit cell volume,
confirming that this two-substructure model captures the basic thermal
properties. Comparison with phonon calculations reveals that the soft
substructure is associated with the low energy phonon modes that are
responsible for the thermal transport. This suggests that searching for
materials containing highly divergent bond distances should be a fruitful route
for discovering low thermal conductivity materials.Comment: Accepted by Applied Physics Letter
Valence bond glass on an fcc lattice in the double perovskite Ba2YMoO6
Peer reviewedPublisher PD
Rapid generation of angular momentum in bounded magnetized plasma
Direct numerical simulations of two-dimensional decaying MHD turbulence in
bounded domains show the rapid generation of angular momentum in
nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this
mechanism. On a larger time scale, the generation of a magnetic angular
momentum, or angular field, is observed. For axisymmetric geometries, the
generation of angular momentum is absent; nevertheless, a weak magnetic field
can be observed. The derived evolution equations for both the angular momentum
and angular field yield possible explanations for the observed behavior
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
Theoretical investigation of magnetic order in ReOFeAs, Re = Ce, Pr
Density functional theory (DFT) calculations are carried out on ReOFeAs, Re =
Ce, Pr, the parent compounds of the high-T superconductors
ReOFFeAs, in order to determine the magnetic order of the ground
state. It is found that the magnetic moments on the Fe sites adopt a collinear
antiferromagnetic order, similar to the case of LaOFeAs. Within the generalized
gradient approximation along with Coulomb onsite repulsion (GGA+U), we show
that the Re magnetic moments also adopt an antiferromagnetic order for which,
within the ReO layer, same spin Re sites lie along a zigzag line perpendicular
to the Fe spin stripes. While within GGA the Re 4f band crosses the Fermi
level, upon inclusion of onsite Coulomb interaction the 4f band splits and
moves away from the Fermi level, making ReOFeAs a Mott insulator.Comment: 5 pages, 4 figure
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