2,999 research outputs found
Synthesis and structural characterization of 2Dioxane.2H2O.CuCl2: metal-organic compound with Heisenberg antiferromagnetic S=1/2 chains
A novel organometallic compound 2Dioxane.CuCl2.2H2O has been synthesized and
structurally characterized by X-ray crystallography. Magnetic susceptibility
and zero-field inelastic neutron scattering have also been used to study its
magnetic properties. It turns out that this material is a weakly coupled
one-dimensional S=1/2 Heisenberg antiferromagnetic chain system with chain
direction along the crystallographic c axis and the nearest-neighbor
intra-chain exchange constant J=0.85(4) meV. The next-nearest-neighbor
inter-chain exchange constant J' is also estimated to be 0.05 meV. The observed
magnetic excitation spectrum from inelastic neutron scattering is in excellent
agreement with numerical calculations based on the Muller ansatz.Comment: 4 pages; 5 figure
Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure
New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.Comment: RevTeX, 4 figures, submitted to Physical Review Letters July 12, 200
Bulk Superconductivity at 14 K in Single Crystals of Fe1+yTexSe1-x
Resistivity, magnetic susceptibility and heat capacity measurements are
reported for single crystals of Fe1+yTexSe1-x grown via a modified Bridgeman
method with 0 < y < 0.15, and x= 1, 0.9, 0.75, 0. 67, 0.55 and 0.5. Although
resistivity measurements show traces of superconductivity near 14 K for all x
except x=1, only crystals grown with compositions near x=0.5 exhibit bulk
superconductivity. The appearance of bulk superconductivity correlates with a
reduction in the magnitude of the magnetic susceptibility at room temperature
and smaller values of y, the concentration of Fe in the Fe(2) site.Comment: Submitted to Phys. Rev.
Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is
on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein
modes; yet only for the Eu and Sr systems is there a large dip in the thermal
conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here
we argue that it is the off-center displacement that is crucial for
understanding this unexplained difference in behavior. It enhances the coupling
between the "rattler" motion and the lattice phonons for the Eu and Sr systems,
and turns on/off another scattering mechanism (for 1K < T < 20K) produced by
the presence/absence of off-center sites. The random occupation of different
off-center sites produces a high density of symmetry-breaking defects which
scatters phonons. It may also be important for improving our understanding of
other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened
arguments regarding need for additional phonon scattering mechanis
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