247 research outputs found
1H-NMR Study on the Magnetic Order in the Mixture of Two Spin Gap Systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3
The antiferromagnetic ordering in the solid-solution of the two spin-gap
systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3 has been investigated by 1H-NMR.
The sample with the Cl-content ratio x=0.85 showed a clear splitting in spectra
below TN=13.5 K, where the spin-lattice relaxation rate T1-1 showed a diverging
behavior. The critical exponent of the temperature dependence of the hyperfine
field is found to be 0.33.Comment: 11pages, 4 figure
H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH)CHNHCu(ClBr)
Spin-lattice relaxation rate of H-NMR has been measured in
(CH)CHNHCu(ClBr) with , which has been
reported to be gapped system with singlet ground state from the previous
macroscopic magnetization and specific heat measurements, in order to
investigate the bond randomness effect microscopically in the gapped composite
Haldane system (CH)CHNHCuCl. It was found that the spin-lattice
relaxation rate in the present system includes both fast and slow
relaxation parts indicative of the gapless magnetic ground state and the gapped
singlet ground state, respectively. We discuss the obtained results with the
previous macroscopic magnetization and specific heat measurements together with
the microscopic SR experiments.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. vol.76
(2007) No.
IPA-CuCl: a S=1/2 Ladder with Ferromagnetic Rungs
The spin gap material IPA-CuCl3 has been extensively studied as a
ferromagnetic-antiferromagnetic bondalternating S = 1/2 chain. This description
of the system was derived from structural considerations and bulk measurements.
New inelastic neutron scattering experiments reveal a totally different
picture: IPA-CuCl3 consists of weakly coupled spin ladders with
antiferromagnetic legs and ferromagnetic rungs. The ladders run perpendicular
to the originally supposed bondalternating chain direction. The ferromagnetic
rungs make this system equivalent to a Haldane S = 1 antiferromagnet. With a
gap energy of 1.17(1) meV, a zone-boundary energy of 4.1(1) meV, and almost no
magnetic anisotropy, IPA-CuCl3 may the best Haldane-gap material yet, in terms
of suitability for neutron scattering studies in high magnetic fields.Comment: 2 pages, 2 figures, submitted to proceedings of LT24, Orlando, FL,
August 200
Dynamics of composite Haldane spin chains in IPA-CuCl3
Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl3
are studied by cold neutron inelastic scattering. Strongly dispersive gap
excitations are observed. Contrary to previously proposed models, the system is
best described as an asymmetric quantum spin ladder. The observed spectrum is
interpreted in terms of ``composite'' Haldane spin chains. The key difference
from actual S=1 chains is a sharp cutoff of the single-magnon spectrum at a
certain critical wave vector.Comment: 4 pages 4 figure
Muon spin relaxation and rotation study on the solid solution of the two spin-gap systems (CH3)2CHNH3-CuCl3 and (CH3)2CHNH3-CuBr3
Muon-spin-rotation and relaxation studies have been performed on
(CH)CHNHCu(ClBr) with =0.85 and 0.95, which are
solid solutions of the two isomorphic spin-gap systems
(CH)CHNHCuCl and (CH)CHNHCuBr with different
spin gaps. The sample with =0.85 showed a clear muon spin rotation under
zero-field below =11.65K, indicating the existence of a long-range
antiferromagnetic order. A critical exponent of the hyperfine field was
obtained to be =0.33, which agrees with 3D-Ising model. In the other
sample with =0.95, an anomalous enhancement of the muon spin relaxation was
observed at very low temperatures indicating a critical slowing down due to a
magnetic instability of the ground state
Effect of pressure on the quantum spin ladder material IPA-CuCl3
Inelastic neutron scattering and bulk magnetic susceptibility studies of the
quantum S=1/2 spin ladder system IPA-CuCl3 are performed under hydrostatic
pressure. The pressure dependence of the spin gap is determined. At
GPa it is reduced to meV from meV at
ambient pressure. The results allow us to predict a soft-mode quantum phase
transition in this system at P GPa. The measurements are
complicated by a proximity of a structural phase transition that leads to a
deterioration of the sample.Comment: 5 pages, 4 figure
Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain
The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure
Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders
The weakly coupled quasi-one-dimensional spin ladder compound
(CH)CHNHCuCl is studied by neutron scattering in magnetic
fields exceeding the critical field of Bose-Einstein condensation of magnons.
Commensurate long-range order and the associated Goldstone mode are detected
and found to be similar to those in a reference 3D quantum magnet. However, for
the upper two massive magnon branches the observed behavior is totally
different, culminating in a drastic collapse of excitation bandwidth beyond the
transition point.Comment: 4 pages, 4 figure
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