553 research outputs found
Magnetocaloric properties of (RE)GaO (RE=Tb,Gd,Nd,Dy)
We report the characteristic magnetic properties of several members of the
rare earth garnet family, GdGaO (GGG), DyGaO
(DGG), TbGaO (TGG), and NdGaO (NGG), and compare
their relative potential utility for magnetocaloric cooling, including their
minimal adiabatic demagnetisation refrigeration (ADR) temperatures and relative
cooling parameters. A main objective of this work was to find potential
improvements over the magnetocaloric properties of GGG for use in low
temperature ADR cryostats. Using Tb and Dy in the RE-site offers
in principle higher saturation magnetisation and Nd gives a lower de
Gennes factor and therefore potentially low transition temperature. Our results
show that DyGaO yields an optimal relative cooling parameter
() at low applied fields and a low transition temperature, which would
allow for the design of more efficient ADR cryostats.Comment: 10 pages, 10 figures, submitted to Physical Review Applie
Optimized signal deduction procedure for the MIEZE neutron spectroscopy technique
We report a method to determine the phase and amplitude of sinusoidally
modulated event rates, binned into 4 bins per oscillation. The presented
algorithm relies on a reconstruction of the unknown parameters. It omits a
calculation intensive fitting procedure and avoids contrast reduction due to
averaging effects. It allows the current data acquisition bottleneck to be
relaxed by a factor of 4. Here, we explain the approach in detail and compare
it to the established fitting procedures of time series having 4 and 16 time
bins per oscillation. In addition we present the empirical estimates of the
errors of the three methods and compare them to each other. We show that the
reconstruction is unbiased, asymptotic, and efficient for estimating the phase.
Reconstructing the contrast, which corresponds to the amplitude of the
modulation, is roughly 10% less efficient than fitting 16 time binned
oscillations. Finally, we give analytical equations to estimate the error for
phase and contrast as a function of their initial values and counting
statistics.Comment: 14 pages, 5 figures, submitted to IOP Measurement Science and
Technolog
Correlation between bulk thermodynamic measurements and the low temperature resistance plateau in SmB6
Topological insulators are materials characterized by dissipationless,
spin-polarized surface states resulting from non-trivial band topologies.
Recent theoretical models and experiments suggest that SmB6 is the first
topological Kondo insulator, in which the topologically non-trivial band
structure results from electron-electron interactions via Kondo hybridization.
Here, we report that the surface conductivity of SmB6 increases systematically
with bulk carbon content. Further, addition of carbon is linked to an increase
in n-type carriers, larger low temperature electronic contributions to the
specific heat with a characteristic temperature scale of T* = 17 K, and a
broadening of the crossover to the insulating state. Additionally, X-ray
absorption spectroscopy shows a change in Sm valence at the surface. Our
results highlight the importance of phonon dynamics in producing a Kondo
insulating state and demonstrate a correlation between the bulk thermodynamic
state and low temperature resistance of SmB6
Magnetic excitations of the Cu quantum spin chain in SrCuPtO
We report the magnetic excitation spectrum as measured by inelastic neutron
scattering for a polycrystalline sample of SrCuPtO. Modeling the data
by the 2+4 spinon contributions to the dynamical susceptibility within the
chains, and with interchain coupling treated in the random phase approximation,
accounts for the major features of the powder-averaged structure factor. The
magnetic excitations broaden considerably as temperature is raised, persisting
up to above 100 K and displaying a broad transition as previously seen in the
susceptibility data. No spin gap is observed in the dispersive spin excitations
at low momentum transfer, which is consistent with the gapless spinon continuum
expected from the coordinate Bethe ansatz. However, the temperature dependence
of the excitation spectrum gives evidence of some very weak interchain
coupling.Comment: 9 pages, 5 figure
Fluorescent carbon dioxide indicators
Over the last decade, fluorescence has become the dominant tool in biotechnology and medical imaging. These exciting advances have been underpinned by the advances in time-resolved techniques and instrumentation, probe design, chemical / biochemical sensing, coupled with our furthered knowledge in biology. Complementary volumes 9 and 10, Advanced Concepts of Fluorescence Sensing: Small Molecule Sensing and Advanced Concepts of Fluorescence Sensing: Macromolecular Sensing, aim to summarize the current state of the art in fluorescent sensing. For this reason, Drs. Geddes and Lakowicz have invited chapters, encompassing a broad range of fluorescence sensing techniques. Some chapters deal with small molecule sensors, such as for anions, cations, and CO2, while others summarize recent advances in protein-based and macromolecular sensors. The Editors have, however, not included DNA or RNA based sensing in this volume, as this were reviewed in Volume 7 and is to be the subject of a more detailed volume in the near future
Frustrated Magnetism in Mott Insulating (VCr)O
V2O3 famously features all four combinations of paramagnetic vs
antiferromagnetic, and metallic vs insulating states of matter in response to
%-level doping, pressure in the GPa range, and temperature below 300 K. Using
time-of-flight neutron spectroscopy combined with density functional theory
calculations of magnetic interactions, we have mapped and analyzed the
inelastic magnetic neutron scattering cross section over a wide range of energy
and momentum transfer in the chromium stabilized antiferromagnetic and
paramagnetic insulating phases (AFI & PI). Our results reveal an important
magnetic frustration and degeneracy of the PI phase which is relieved by the
rhombohedral to monoclinic transition at K due to a significant
magneto-elastic coupling. This leads to the recognition that magnetic
frustration is an inherent property of the paramagnetic phase in and plays a key role in suppressing the magnetic long range
ordering temperature and exposing a large phase space for the paramagnetic Mott
metal-insulator transition to occur.Comment: 16 pages, 11 figure
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