160 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.
Spin-strain coupling in NiCl2-4SC(NH2)2
We report results of ultrasonic investigations of the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2, also known as DTN, in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the [001] direction induces a transition into an antiferromagnetic phase with T(N)max ≈ 1.2 K. Accordingly, at T = 0 there are two quantum critical points at ~2.1 T and at ~12.6 T. The acoustic c33 mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound wave. The H-T phase diagram obtained from our measurements is compared with results from other experimental investigations and the low-temperature acoustic anomalies are traced up to T > T(N). We also report frequency-dependent effects, which open the possibility to investigate the spin fluctuations in the critical regions. Our observations show an important role of the spin-phonon coupling in DTN
Character of magnetic excitations in a quasi-one-dimensional antiferromagnet near the quantum critical points: Impact on magneto-acoustic properties
We report results of magneto-acoustic studies in the quantum spin-chain
magnet NiCl-4SC(NH) (DTN) having a field-induced ordered
antiferromagnetic (AF) phase. In the vicinity of the quantum critical points
(QCPs) the acoustic mode manifests a pronounced softening accompanied
by energy dissipation of the sound wave. The acoustic anomalies are traced up
to , where the thermodynamic properties are determined by fermionic
magnetic excitations, the "hallmark" of one-dimensional (1D) spin chains. On
the other hand, as established in earlier studies, the AF phase in DTN is
governed by bosonic magnetic excitations. Our results suggest the presence of a
crossover from a 1D fermionic to a 3D bosonic character of the magnetic
excitations in DTN in the vicinity of the QCPs.Comment: 5 pages, 4 figures. Accepted for publication by Phys. Rev
Magnetoelectric effects in an organo-metallic quantum magnet
We observe a bilinear magnetic field-induced electric polarization of 50 in single crystals of NiCl-4SC(NH) (DTN). DTN forms a
tetragonal structure that breaks inversion symmetry, with the highly polar
thiourea molecules all tilted in the same direction along the c-axis.
Application of a magnetic field between 2 and 12 T induces canted
antiferromagnetism of the Ni spins and the resulting magnetization closely
tracks the electric polarization. We speculate that the Ni magnetic forces
acting on the soft organic lattice can create significant distortions and
modify the angles of the thiourea molecules, thereby creating a magnetoelectric
effect. This is an example of how magnetoelectric effects can be constructed in
organo-metallic single crystals by combining magnetic ions with electrically
polar organic elements.Comment: 3 pages, 3 figure
Interplay of Spin and Lattice Degrees of Freedom in the Frustrated Antiferromagnet CdCr_2O_4: High-field and Temperature Induced Anomalies of the Elastic Constants
Temperature and magnetic field studies of the elastic constants of the
chromium spinel CdCr_2O_4 show pronounced anomalies related to strong
spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison
of the longitudinal acoustic mode propagating along the [111] direction with
theory based on an exchange-striction mechanism leads to an estimate of the
strength of the magneto-elastic interaction. The derived spin-phonon coupling
constant is in good agreement with previous determinations based on infrared
absorption. Further insight is gained from intermediate and high magnetic field
experiments in the field regime of the magnetization plateau. The role of the
antisymmetric Dzyaloshinskii-Moriya interaction discussed and we compare the
spin-phonon coupling in CdCr_2O_4 in both the ordered and disordered states.Comment: 12 pages, 8 figures; Appendix added,To appear in Phys Rev.
Genetic variability of the ovine αs1-casein
The casein genetic polymorphisms are important for their effects on quantitative traits and technological properties of milk. At the αs1-casein (CSN1S1) level three genetic variants were characterised (A, C, D) in ovine milk (Ferranti et al., 1995)
Lattice Boltzmann models for non-ideal fluids with arrested phase-separation
The effects of mid-range repulsion in Lattice Boltzmann models on the
coalescence/breakup behaviour of single-component, non-ideal fluids are
investigated. It is found that mid-range repulsive interactions allow the
formation of spray-like, multi-droplet configurations, with droplet size
directly related to the strength of the repulsive interaction. The simulations
show that just a tiny ten-percent of mid-range repulsive pseudo-energy can
boost the surface/volume ratio of the phase- separated fluid by nearly two
orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems,
a pseudo-potential energy is defined, which is found to behave like a
quasi-conserved quantity for most of the time-evolution. This offers a useful
quantitative indicator of the stability of the various configurations, thus
helping the task of their interpretation and classification. The present
approach appears to be a promising tool for the computational modelling of
complex flow phenomena, such as atomization, spray formation and
micro-emulsions, break-up phenomena and possibly glassy-like systems as well.Comment: 12 pages, 9 figure
Characterization of the casein gene complex in West Africa goats and description of a new αs1-casein polymorphism
The analysis of casein polymorphisms was carried
out in West Africa goat populations: Red Sokoto (n =
57), West African Dwarf Nigeria (n = 27), West African
Dwarf Cameroon (n = 39), and Borno (n = 37). The 4
casein genes alphas1 (CSN1S1), beta (CSN2), alphas2 (CSN1S2), and kappa (CSN3) were typed at the DNA level. No null alleles were found in any of the genes analyzed. A PCR single-strand conformation polymorphism method was
implemented for the identification of CSN1S1*F allele
simultaneously with A/01, B/E, N and the new allele.
The allele differed from CSN1S1*B by a synonymous
transversion TCG->TCT in the codon corresponding to
Ser66 of the mature protein. The new allele, named
CSN1S1*B', occurred at a high frequency in all the
populations, ranging from 0.295 (West African Dwarf
Cameroon) to 0.405 (Borno). A greater frequency was
found for alleles associated with high alphas1-casein quantity,
as has already been observed in the goat populations
from the Mediterranean area. The intermediate
E allele occurred only in the Red Sokoto and at a low
frequency. The faint F allele occurred in 3 populations
at frequencies lower than 0.03. Linkage disequilibrium
occurred in all the populations, with highly significant
differences in Borno, Red Sokoto, and West Africa
Dwarf Nigeria, and significant differences in West Africa
Dwarf Cameroon. Only 10 haplotypes showed frequencies
>= 0.05 in at least 1 of the 4 populations considered,
and the overall frequency was >0.1 only for 4
haplotypes: BAAB, B'ACA, ACAB, and BACA (in the
order CSN1S1-CSN2-CSN1S2-CSN3). Haplotype
BAAB, postulated as an ancestral haplotype in previous
studies, was the most common haplotype in all breeds
except Borno, where B'ACA was predominant. The results
obtained are of considerable significance given that very little information exists on the subject for African goats. The high frequency of strong alleles in the calcium-sensitive caseins as well as the high linkage disequilibrium found among the casein genes in the African breeds analyzed may suggest that specific casein haplotypes have already been selected due to their advantages for nutrition. Haplotypes providing greater
protein and casein content would increase the energy
content of milk, thus resulting in more favorable growth
and survival of young goats and humans consuming
the milk
Are violations to temporal Bell inequalities there when somebody looks?
The possibility of observing violations of temporal Bell inequalities,
originally proposed by Leggett as a mean of testing the quantum mechanical
delocalization of suitably chosen macroscopic bodies, is discussed by taking
into account the effect of the measurement process. A general criterion
quantifying this possibility is defined and shown not to be fulfilled by the
various experimental configurations proposed so far to test inequalities of
different forms.Comment: 7 pages, 1 eps figure, needs europhys.sty and euromacr.tex, enclosed
in the .tar.gz file; accepted for publication in Europhysics Letter
- …