71 research outputs found
Spin Dynamics in Chains with Next-Nearest-Neighbor Exchange Interactions
Low-energy magnetic excitations in the spin-1/2 chain compound
(CHN)CuCl [known as (6MAP)CuCl] are probed by means of
tunable-frequency electron spin resonance. Two modes with asymmetric (with
respect to the line) frequency-field dependences are resolved,
illuminating the striking incompatibility with a simple uniform
Heisenberg chain model. The unusual ESR spectrum is explained in terms of the
recently developed theory for spin-1/2 chains, suggesting the important role of
next-nearest-neighbor interactions in this compound. Our conclusion is
supported by model calculations for the magnetic susceptibility of
(6MAP)CuCl, revealing a good qualitative agreement with experiment
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
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.
Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
antiferromagnetic chain with alternating -tensor and Dzyaloshinskii-Moriya
interactions that exhibits a field-induced spin gap, are probed by means of
pulsed-field electron spin resonance spectroscopy. In particular, we report on
a minimum of the gap in the vicinity of the saturation field T
associated with a transition from the sine-Gordon region (with soliton-breather
elementary excitations) to a spin-polarized state (with magnon excitations).
This interpretation is fully confirmed by the quantitative agreement over the
entire field range of the experimental data with the DMRG investigation of the
spin-1/2 Heisenberg chain with a staggered transverse field
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
Electron Spin Resonance in a Spin-1/2 Heisenberg Strong-rung Ladder
Cu(CHN)Cl, a strong-rung spin-1/2 Heisenberg ladder compound,
is probed by means of electron spin resonance (ESR) spectroscopy in the
field-induced gapless phase above . The temperature dependence of the
ESR linewidth is analyzed in the quantum field theory framework, suggesting
that the anisotropy of magnetic interactions plays a crucial role, determining
the peculiar low-temperature ESR linewidth behavior. In particular, it is
argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on
the bonds along the ladder legs) can be the source of this behavior in
Cu(CHN)Cl
Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl-4SC(NH)
NiCl-4SC(NH) (DTN) is a quantum S=1 chain system with strong
easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of
the spin degrees of freedom. ESR studies of magnetic excitations in DTN in
fields up to 25 T are presented. Based on analysis of the single-magnon
excitation mode in the high-field spin-polarized phase and previous
experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of
spin-Hamiltonian parameters is obtained. Our results yield K,
K, and K for the anisotropy, intrachain, and interchain exchange
interactions, respectively. These values are used to calculate the
antiferromagnetic phase boundary, magnetization and the frequency-field
dependence of two-magnon bound-state excitations predicted by theory and
observed in DTN for the first time. Excellent quantitative agreement with
experimental data is obtained
Ultrasonic investigations of spin-ices DyTiO and HoTiO in and out of equilibrium
We report ultrasound studies of spin-lattice and single-ion effects in the
spin-ice materials DyTiO (DTO) and HoTiO (HTO) across a
broad field range up to 60 T, covering phase transformations, interactions with
low-energy magnetic excitations, as well as single-ion effects. In particular,
a sharp dip observed in the sound attenuation in DTO at the gas-liquid
transition of the magnetic monopoles is explained based on an approach
involving negative relaxation processes. Furthermore, quasi-periodic peaks in
the acoustic properties of DTO due to non-equilibrium processes are found to be
strongly affected by {\em macroscopic} thermal-coupling conditions: the thermal
runaway observed in previous studies in DTO can be suppressed altogether by
immersing the sample in liquid helium. Crystal-electric-field effects having
higher energy scale lead to a renormalization of the sound velocity and sound
attenuation at very high magnetic fields. We analyze our observations using an
approach based on an analysis of exchange-striction couplings and single-ion
effects
ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase
Magnetic excitations in the strong-leg quantum spin ladder compound
(CHN)CuBr (known as DIMPY) in the field-induced
Tomonaga-Luttinger spin liquid phase are studied by means of high-field
electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode
with unusual non-linear frequency-field dependence is revealed experimentally.
Using a combination of analytic and exact diagonalization methods, we compute
the dynamical structure factor and identify this mode with longitudinal
excitations in the antisymmetric channel. We argue that these excitations
constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2
Heisenberg antiferromagnetic ladder and owe its ESR observability to the
uniform Dzyaloshinskii-Moriya interaction
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