2,145 research outputs found
Field-induced commensurate long-range order in the Haldane-gap system NDMAZ
High-field neutron diffraction studies of the new quantum-disordered S=1
linear-chain antiferromagnet Ni(CHN)N(ClO) (NDMAZ)
are reported. At T=70 mK, at a critical field T applied along the
(013) direction, a phase transition to a commensurate N\'{e}el-like ordered
state is observed. The results are discussed in the context of existing
theories of quantum phase transitions in Haldane-gap antiferromagnets, and in
comparions with previous studies of the related system
Ni(CHN)N(PF)
Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet
We have measured the heat capacity and magnetization of the spin one
one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic
field versus temperature phase diagram. We found a field induced long-range
magnetic ordering. We have been successful in explaining the phase diagram
theoretically.Comment: 6 pages, 18 figure
High-field phase diagram of the Haldane-gap antiferromagnet
We have determined the magnetic phase diagram of the quasi-one-dimensional
1 Heisenberg antiferromagnet by
specific heat measurements to 150 mK in temperature and 32 T in magnetic field.
When field is applied along the spin-chain direction, a new phase appears at
T. For the previously known phases of field-induced order,
accurate determination is made of the power-law exponents of the ordering
temperature near the zero-temperature critical field , owing to the
four-fold improvement of the minimum temperature over the previous work. The
results are compared with the predictions based on the Bose-Einstein
condensation of triplet excitations. Substituting deuterium for hydrogen is
found to slightly reduce the interchain exchange.Comment: 6 pages, 6 figure
Field-induced 3- and 2-dimensional freezing in a quantum spin liquid
Field-induced commensurate transverse magnetic ordering is observed in the
Haldane-gap compound \nd by means of neutron diffraction. Depending on the
direction of applied field, the high-field phase is shown to be either a
3-dimensional ordered N\'{e}el state or a short-range ordered state with
dominant 2-dimensional spin correlations. The structure of the high-field phase
is determined, and properties of the observed quantum phase transition are
discussed.Comment: 4 pages 3 figure
Spin-Reorientation Transition of Field-Induced Magnetic Ordering Phases in the Anisotropic Haldane System
A possible spin-reorientation transition in field-induced magnetic ordering
phases of the S=1 Haldane system with large easy-plane anisotropy is proposed,
using an effective Lagrangian formalism as well as the density matrix
renormalization group method. Such a spin-reorientation transition is predicted
in the case where the applied magnetic field is inclined from the easy axis of
the anisotropy. We point out that this transition has a close connection with a
variation of the order parameter even at zero temperature, although it is
different from a quantum analog of the so-called spin-flop transition proposed
for the system having a strong easy axis anisotropy. In connection with a novel
phase observed recently in the Haldane system at high fields, we discuss
possible implications for the field-induced magnetic ordering.Comment: 14 pages, 7 figure
Massive triplet excitations in a magnetized anisotropic Haldane spin chain
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet \nd are performed at mK temperatures in magnetic fields of
almost twice the critical field applied perpendicular to the spin cahins.
Above a re-opening of the spin gap is clearly observed. In the high-field
N\'eel-ordered state the spectrum is dominated by three distinct long-lived
excitation branches. Several field-theoretical models are tested in a
quantitative comparison with the experimental data.Comment: 4 pages, 3 figure
Quasi-elastic neutron scattering in the high-field phase of a Haldane antiferromagnet
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet NDMAP are performed in magnetic fields below and above the
critical field Hc at which the gap closes. Quasi-elastic neutron scattering is
found for H>Hc indicating topological excitations in the high field phase.Comment: Added to discussion section. v2: Updated figure
Field-Induced Transition in the S=1 Antiferromagnetic Chain with Single-Ion Anisotropy in a Transverse Magnetic Field
The field-induced transition in one-dimensional S=1 Heisenberg
antiferromagnet with single-ion anisotropy in the presence of a transverse
magnetic field is obtained on the basis of the Schwinger boson mean-field
theory. The behaviors of the specific heat and susceptibility as functions of
temperature as well as the applied transverse field are explored, which are
found to be different from the results obtained under a longitudinal field. The
anomalies of the specific heat at low temperatures, which might be an
indicative of a field-induced transition from a Luttinger liquid phase to an
ordered phase, are explicitly uncovered under the transverse field. A schematic
phase diagram is proposed. The theoretical results are compared with
experimental observations.Comment: Revtex, 7 figure
Field-induced long-range order in the S=1 antiferromagnetic chain
The quasi-one dimensional S=1 antiferromagnet in magnetic field H is
investigated with the exact diagonalization of finite chains and the mean field
approximation for the interchain interaction. In the presence of the single-ion
anisotropy D, the full phase diagram in the plane is presented for H
\parallel D and H \perp D. The shape of the field-induced long-range ordered
phase is revealed to be quite different between the two cases, as observed in
the recent experiment of NDMAP. The estimated ratio of the interchain and
intrachain couplings of NDMAP (J'/J ~ 10^{-3}) is consistent with the neutron
scattering measurement.Comment: 4 pages, Revtex, with 6 eps figure
Haldane-gap excitations in the low-H_c 1-dimensional quantum antiferromagnet NDMAP
Inelastic neutron scattering on deuterated single-crystal samples is used to
study Haldane-gap excitations in the new S=1 one-dimensional quantum
antiferromagnet NDMAP, that was recently recognized as an ideal model system
for high-field studies. The Haldane gap energies meV,
meV and meV, for excitations polarized along
the a, b, and c crystallographic axes, respectively, are directly measured. The
dispersion perpendicular to the chain axis c is studied, and extremely weak
inter-chain coupling constants meV and meV, along the a and b axes, respectively, are determined. The results
are discussed in the context of future experiments in high magnetic fields.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
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