622 research outputs found
Dynamical properties of S=1 bond-alternating Heisenberg chains in transverse magnetic fields
We calculate dynamical structure factors of the S=1 bond-alternating
Heisenberg chain with a single-ion anisotropy in transverse magnetic fields,
using a continued fraction method based on the Lanczos algorithm. In the
Haldane-gap phase and the dimer phase, dynamical structure factors show
characteristic field dependence. Possible interpretations are discussed. The
numerical results are in qualitative agreement with recent results for
inelastic neutron-scattering experiments on the S=1 bond-alternating
Heisenberg-chain compound and the
S=1 Haldane-gap compound in
transverse magnetic fields.Comment: 7 pages, 6 figure
Specific heat of the spin-dimer antiferromagnet BaMnO in high magnetic fields
We have measured the specific heat of the coupled spin-dimer antiferromagnet
BaMnO to 50 mK in temperature and to 29 T in the magnetic field.
The experiment extends to the midpoint of the field region (25.9 T 32.3 T) of the magnetization plateau at 1/2 of the saturation
magnetization, and reveals the presence of three ordered phases in the field
region between that of the magnetization plateau and the low-field spin-liquid
region. The exponent of the phase boundary with the thermally disordered region
is smaller than the theoretical value based on the Bose-Einstein condensation
of spin triplets. At zero field and 29 T, the specific-heat data show gapped
behaviors characteristic of spin liquids. The zero-field data indicate that the
gapped triplet excitations form two levels whose energies differ by nearly a
factor of two. At least the lower level is well localized. The data at 29 T
reveal that the low-lying excitations at the magnetization plateau are weakly
delocalized.Comment: 6 pages, 5 figures, revised versio
S=1/2 Kagome antiferromagnets CsCu_{12}$ with M=Zr and Hf
Magnetization and specific heat measurements have been carried out on
CsCuZrF and CsCuHfF single crystals, in which
Cu ions with spin-1/2 form a regular Kagom\'{e} lattice. The
antiferromagnetic exchange interaction between neighboring Cu spins is
K and 540 K for CsCuZrF and
CsCuHfF, respectively. Structural phase transitions were
observed at K and 175 K for CsCuZrF and
CsCuHfF, respectively. The specific heat shows a small bend
anomaly indicative of magnetic ordering at K and 24.5 K in
CsCuZrF and CsCuHfF, respectively. Weak
ferromagnetic behavior was observed below . This weak
ferromagnetism should be ascribed to the antisymmetric interaction of the
Dzyaloshinsky-Moriya type that are generally allowed in the Kagom\'{e} lattice.Comment: 6 pages, 4 figure. Conference proceeding of Highly Frustrated
Magnetism 200
Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet
The magnetization process of the isotropic Heisenberg antiferromagnet on the
kagome lattice is studied. Data obtained from the numerical-diagonalization
method are reexamined from the viewpoint of the derivative of the magnetization
with respect to the magnetic field. We find that the behavior of the derivative
at approximately one-third of the height of the magnetization saturation is
markedly different from that for the cases of typical magnetization plateaux.
The magnetization process of the kagome-lattice antiferromagnet reveals a new
phenomenon, which we call the "magnetization ramp".Comment: 4 pages, 5figures, accepted in J. Phys. Soc. Jpn
Universal emergence of the one-third plateau in the magnetization process of frustrated quantum spin chains
We present a numerical study of the magnetization process of frustrated
quantum spin-S chains with S=1, 3/2, 2 as well as the classical limit. Using
the exact diagonalization and density-matrix renormalization techniques, we
provide evidence that a plateau at one third of the saturation magnetization
exists in the magnetization curve of frustrated spin-S chains with S>1/2.
Similar to the case of S=1/2, this plateau state breaks the translational
symmetry of the Hamiltonian and realizes an up-up-down pattern in the spin
component parallel to the external field. Our study further shows that this
plateau exists both in the cases of an isotropic exchange and in the easy-axis
regime for spin-S=1, 3/2, and 2, but is absent in classical frustrated spin
chains with isotropic interactions. We discuss the magnetic phase diagram of
frustrated spin-1 and spin-3/2 chains as well as other emergent features of the
magnetization process such as kink singularities, jumps, and even-odd effects.
A quantitative comparison of the one-third plateau in the easy-axis regime
between spin-1 and spin-3/2 chains on the one hand and the classical frustrated
chain on the other hand indicates that the critical frustration and the phase
boundaries of this state rapidly approach the classical result as the spin S
increases.Comment: 15 pages RevTex4, 13 figure
Magnetization plateaus as insulator-superfluid transitions in quantum spin systems
We study the magnetization process in two-dimensional S=1/2 spin systems, to
discuss the appearance of a plateau structure. The following three cases are
considered: (1) the Heisenberg antiferromagnet and multiple-spin exchange model
on the triangular lattice, (2) Shastry-Sutherland type lattice, [which is a
possible model for SrCu2(BO3)2,] (3) 1/5-depleted lattice (for CaV4O9). We find
in these systems that magnetization plateaus can appear owing to a transition
from superfluid to a Mott insulator of magnetic excitations. The plateau states
have CDW order of the excitations. The magnetizations of the plateaus depend on
components of the magnetic excitations, range of the repulsive interaction, and
the geometry of the lattice.Comment: 5 pages, RevTeX, 7 figures, note and reference adde
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