59 research outputs found
Magnetoacoustics of the Low-Dimensional Quantum Antiferromagnet Cs2CuCl4 with Spin Frustration
We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice spin-1/2 antiferromagnet Cs₂CuCl₄ (T<sub>N</sub> = 0.6 K), in external magnetic fields up to 14 T, applied along the <em>b</em> axis, and at temperatures down to 300 mK. The results are analyzed with a quasi-two-dimensional hard-core boson theory based on exchange-striction coupling. There is a good qualitative agreement between theoretical and experimental results.Citation: Sytcheva, A. et al. (2010). 'Magnetoacoustics of the low-dimensional quantum antiferromagnet Cs₂CuCl₄', Journal of Low Temperature Physics, 159(1-2), 109-113. [Available at http://www.springer.com/materials/journal/10909]. © The Authors 2010. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any non-commercial use, distribution, and reproduction in any medium, provided the original authors and source are credited.
Magnetic phase transitions in the two-dimensional frustrated quantum antiferromagnet Cs2CuCl4
We report magnetization and specific heat measurements in the 2D frustrated
spin-1/2 Heisenberg antiferromagnet Cs2CuCl4 at temperatures down to 0.05 K and
high magnetic fields up to 11.5 T applied along a, b and c-axes. The low-field
susceptibility chi (T) M/B shows a broad maximum around 2.8 K characteristic of
short-range antiferromagnetic correlations and the overall temperature
dependence is well described by high temperature series expansion calculations
for the partially frustrated triangular lattice with J=4.46 K and J'/J=1/3. At
much lower temperatures (< 0.4 K) and in in-plane field (along b and c-axes)
several new intermediate-field ordered phases are observed in-between the
low-field incommensurate spiral and the high-field saturated ferromagnetic
state. The ground state energy extracted from the magnetization curve shows
strong zero-point quantum fluctuations in the ground state at low and
intermediate fields
The Quasi-1D S=1/2 Antiferromagnet Cs2CuCl4 in a Magnetic Field
Magnetic excitations of the quasi-1D S=1/2 Heisenberg antiferromagnet (HAF)
Cs2CuCl4 have been measured as a function of magnetic field using neutron
scattering. For T<0.62 K and B=0 T the weak inter-chain coupling produces 3D
incommensurate ordering. Fields greater than Bc =1.66 T, but less than the
field (~8 T) required to fully align the spins, are observed to decouple the
chains, and the system enters a disordered intermediate-field phase (IFP). The
IFP excitations are in agreement with the predictions of Muller et al. for the
1D S=1/2 HAF, and Talstra and Haldane for the related 1/r^2 chain (the
Haldane-Shastry model). This behaviour is inconsistent with linear spin-wave
theory.Comment: 10 pages, 4 encapsulated postscript figures, LaTeX, to be published
in PRL, e-mail comments to [email protected]
Bose-Einstein Condensation of Magnons in Cs2CuCl4
We report on results of specific heat measurements on single crystals of the
frustrated quasi-2D spin-1/2 antiferromagnet Cs_2CuCl_4 (T_N=0.595 K) in
external magnetic fields B30 mK. Decreasing B from
high fields leads to the closure of the field-induced gap in the magnon
spectrum at a critical field B_c = 8.51 T and a magnetic phase transition is
clearly seen below B_c. In the vicinity to B_c, the phase transition boundary
is well described by the power-law T_c(B)\propto (B_c-B)^{1/\phi} with the
measured critical exponent \phi\simeq 1.5. These findings are interpreted as a
Bose-Einstein condensation of magnons.Comment: 5 pages, 4 figures, experiment and theor
Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields
We explore the effects of noncommuting applied fields on the ground-state
ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4
using single-crystal neutron diffraction. In zero field interchain couplings
cause long-range order below T_N=217(5) mK with chains ordered
antiferromagnetically along their length and moments confined to the (b,c)
plane. Magnetic fields applied at an angle to the XY planes are found to
initially stabilize the order by promoting a spin-flop phase with an increased
perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic
order becomes unstable and a transition occurs to a phase with no long-range
order in the (b,c) plane, proposed to be a spin liquid phase that arises when
the quantum fluctuations induced by the noncommuting field become strong enough
to overcome ordering tendencies. Magnetization measurements confirm that
saturation occurs at much higher fields and that the proposed spin-liquid state
exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is
discussed in terms of known results on XY-like chains in coexisting
longitudinal and transverse fields.Comment: revtex, 14 figures, 2 tables, to appear in Phys. Rev.
Investigating the level of signal-to-noise ratio performance of a quadrature head coil in MRI
The following study sought to investigate the level of SNR performance obtainable from a particular MR system (1.5 T GE Signa Horizon™) using the system's quadrature head coil only. The method used for identifying the level of SNR performance of the particular system's quadrature head coil was the same method employed by MagNET (the subdivision of Medical Devices Agency which is responsible for MR technology) in order to produce the official evaluation reports for all MR systems currently available. The SNR test method is based on the National Electrical Manufacturers Association (NEMA) standard for SNR measurements. Therefore, a comparison of the results from this study with the results available in the MDA evaluation report for this particular MR system would ultimately reveal the true SNR performance at the time of testing. SNR measurements in all three imaging planes were obtained and despite the insignificant deviation in the axial plane which was 2.9%, the SNR performance in the sagittal and coronal planes was found to be below the expected, and were 15.2% and 11.6% respectively. This deviation can be related to a number of factors which will be presented. © Greenwich Medical Media Ltd. 2004
Order and excitations near quantum criticality in quasi-1D S=1/2 easy-plane antiferromagnet Cs2CoCl4
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