168 research outputs found
Pressure-Induced Magnetic Quantum Phase Transitions from Gapped Ground State in TlCuCl3
Magnetization maesurements under hydrostatic pressure were performed on an
S=1/2 coupled spin system TlCuCl3 with a gapped ground state under magnetic
field H parallel to the [2,0,1] direction. With increasing applied pressure P,
the gap decreases and closes completely at Pc=0.42 kbar. For P>Pc, TlCuCl3
undergoes antiferromagnetic ordering. A spin-flop transition was observed at
Hsf=0.7T. The spin-flop field is approximately independent of pressure,
although the sublattice magnetization increases with pressure. The gap and Neel
temperature are presented as function is attributed to to the relative
enhancement of the interdimer exchange interactions compared with the
intradimer exchange interaction.Comment: 4pages,3figures To be published in J. Phys. Soc. Jpn. Vol.73 No.1
Neutron Diffraction Study of the Pressure-Induced Magnetic Ordering in the Spin Gap System TlCuCl
Neutron elastic scattering measurements have been performed under the
hydrostatic pressure in order to investigate the spin structure of the
pressure-induced magnetic ordering in the spin gap system TlCuCl. Below the
ordering temperature K for the hydrostatic pressure
GPa, magnetic Bragg reflections were observed at the reciprocal lattice points
{\mib Q}=(h, 0, l) with integer and odd , which are equivalent to
those points with the lowest magnetic excitation energy at ambient pressure.
This indicates that the spin gap closes due to the applied pressure. The spin
structure of the pressure-induced magnetic ordered state for GPa was
determined.Comment: 4 pages, 3 figures, 3 eps files, jpsj2.cls styl
Frustration-Induced Two Dimensional Quantum Disordered Phase in Piperazinium Hexachlorodicuprate
Piperazinium Hexachlorodicuprate (PHCC) is shown to be a frustrated
quasi-two-dimensional quantum Heisenberg antiferromagnet with a gapped
spectrum. Zero-field inelastic neutron scattering and susceptibility and
specific heat measurements as a function of applied magnetic field are
presented. At T = 1.5 K, the magnetic excitation spectrum is dominated by a
single propagating mode with a gap, Delta = 1 meV, and bandwidth of
approximately 1.8 meV in the (h0l) plane. The mode has no dispersion along the
b* direction indicating that neighboring a-c planes of the triclinic structure
are magnetically decoupled. The heat capacity shows a reduction of the gap as a
function of applied magnetic field in agreement with a singlet-triplet
excitation spectrum. A field-induced ordered phase is observed in heat capacity
and magnetic susceptibility measurements for magnetic fields greater than H_c1
approximately equal to 7.5 Tesla. Analysis of the neutron scattering data
reveals the important exchange interactions and indicates that some of these
are highly frustrated.Comment: 13 pages with 14 figures, 7 pages of text, 6 pages of figures.
Submitted to Phys. Rev. B 4/7/2001. email comments to [email protected] or
[email protected]
Magnetization plateaux in dimerized spin ladder arrays
We investigate the ground state magnetization plateaux appearing in spin 1/2
two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and
dimerized zig-zag interchain couplings. Using both Abelian bosonization and
Lanczos methods we find that the system yields rather unusual plateaux and
exhibits massive and massless phases for specific choices or ``tuning'' of
exchange interactions. The relevance of this behavior in the study of
NH_4CuCl_3 is discussed.Comment: 9 pages, RevTeX, 11 postscript figure
Frustrated 3-Dimensional Quantum Spin Liquid in CuHpCl
Inelastic neutron scattering measurements are reported for the quantum
antiferromagnetic material Cu_2(C_5H_12N_2)_2Cl_4 (CuHpCl). The magnetic
excitation spectrum forms a band extending from 0.9 meV to 1.4 meV. The
spectrum contains two modes that disperse throughout the a-c plane of the
monoclinic unit cell with less dispersion along the unique b-axis. Simple
arguments based on the measured dispersion relations and the crystal structure
show that a spin ladder model is inappropriate for describing CuHpCl. Instead,
it is proposed that hydrogen bond mediated exchange interactions between the
bi-nuclear molecular units yield a three-dimensional interacting spin system
with a recurrent triangular motif similar to the Shastry-Sutherland Model
(SSM). Model independent analysis based on the first moment sum rule shows that
at least four distinct spin pairs are strongly correlated and that two of
these, including the dimer bond of the corresponding SSM, are magnetically
frustrated. These results show that CuHpCl should be classified as a
frustration induced three dimensional quantum spin liquid.Comment: 13 pages, 17 figures (Color) ReSubmitted to Phys. Rev. B 9/21/2001
resubmission has new content email comments to [email protected] or
[email protected]
Critical Properties of Condensation of Field-Induced Triplet Quasiparticles
A review on the field-induced magnetic ordering is given, together with some
results of a quantum Monte Carlo simulation focused on the critical behevior
near the quantum critical point.Comment: Proceedings of SPQS, Sendai, 200
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