327 research outputs found
Effects of Randomness on the Field-Induced Phase Transition in the S=1 Bond-Alternating Spin Chain NTENP
We report novel effects of randomness in the S=1 bond-alternating
antiferromagnetic chain compound with a dimer-singlet ground state
[Ni(N,N'-bis(3-aminopropyl)propane-1,3-diamine(mu-NO2]ClO4 abbreviated as
NTENP. The 15N NMR spectra develop a continuum with sharply peaked edges at low
temperatures, indicating an inhomogeneous staggered magnetization induced by
magnetic field. We attribute this to random anisotropic interactions due to
disorder of NO2 groups in the chains. The field-induced antiferromagnetic
transition exhibits remarkably anisotropic behavior. We propose that a
field-induced incoherent magnetization is transformed into a coherent
antiferromagnetic moment with spatially fluctuating amplitude.Comment: 4pages, 5 figues, submitted to J. Phys. Soc. Jp
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
Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain as a model system for Cu(3-Clpy)(N)
Thermodynamic properties of a tetramer
ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain
are investigated by the use of an exact mapping transformation technique. Exact
results for the magnetization, susceptibility and specific heat in the zero as
well as nonzero magnetic field are presented and discussed in detail. The
results obtained from the mapping are compared with the relevant experimental
data of Cu(3-Clpy)(N) (3-Clpy=3-Chloropyridine).Comment: 10 pages, 1 table, 14 figures, to be presented at CSMAG04 conferenc
Magnetization Plateaus in a Solvable 3-Leg Spin Ladder
We present a solvable ladder model which displays magnetization plateaus at
fractional values of the total magnetization. Plateau signatures are also shown
to exist along special lines. The model has isotropic Heisenberg interactions
with additional many-body terms. The phase diagram can be calculated exactly
for all values of the rung coupling and the magnetic field. We also derive the
anomalous behaviour of the susceptibility near the plateau boundaries. There is
good agreement with the phase diagram obtained recently for the pure Heisenberg
ladders by numerical and perturbative techniques.Comment: 4 pages, revtex, 3 postscript figures, small changes to the text and
references update
Magnetization process for a quasi-one-dimensional S=1 antiferromagnet
We investigate the magnetization process for a quasi-one-dimensional S=1
antiferromagnet with bond alternation. By combining the density matrix
renormalization group method with the interchain mean-field theory, we discuss
how the interchain coupling affects the magnetization curve. It is found that
the width of the magnetization plateau is considerably reduced upon introducing
the interchain coupling. We obtain the phase diagram in a magnetic field. The
effect of single-ion anisotropy is also addressed.Comment: 6 pages, 7 eps figure
A Strong-Coupling Approach to the Magnetization Process of Polymerized Quantum Spin Chains
Polymerized quantum spin chains (i.e. spin chains with a periodic modulation
of the coupling constants) exhibit plateaux in their magnetization curves when
subjected to homogeneous external magnetic fields. We argue that the
strong-coupling limit yields a simple but general explanation for the
appearance of plateaux as well as of the associated quantization condition on
the magnetization. We then proceed to explicitly compute series for the plateau
boundaries of trimerized and quadrumerized spin-1/2 chains. The picture is
completed by a discussion how the universality classes associated to the
transitions at the boundaries of magnetization plateaux arise in many cases
from a first order strong-coupling effective Hamiltonian.Comment: 5 pages REVTeX, three PostScript figures included using psfig.st
Product Wave Function Renormalization Group: construction from the matrix product point of view
We present a construction of a matrix product state (MPS) that approximates
the largest-eigenvalue eigenvector of a transfer matrix T, for the purpose of
rapidly performing the infinite system density matrix renormalization group
(DMRG) method applied to two-dimensional classical lattice models. We use the
fact that the largest-eigenvalue eigenvector of T can be approximated by a
state vector created from the upper or lower half of a finite size cluster.
Decomposition of the obtained state vector into the MPS gives a way of
extending the MPS, at the system size increment process in the infinite system
DMRG algorithm. As a result, we successfully give the physical interpretation
of the product wave function renormalization group (PWFRG) method, and obtain
its appropriate initial condition.Comment: 8 pages, 8 figure
Propiedades ópticas de películas de dióxido de vanadio como recubrimiento termocrómico en ventanas
The optical properties of vanadium dioxide (VO2) thin film have been studied for the potential application of intelligent windows. The results show that VO2 film deposited on sapphire substrates exhibits good thermochromic effects, its IR transmittance changes 60% before and after phase transition, and has less thickness dependence than UV transmittance. Doping can significantly reduce transition temperature, such as to 30°C for 1.5% Mo doped VO2.Se han investigado las propiedades ópticas del dióxido de vanadio (VO2) aplicado como películas delgadas para posibles aplicaciones en ventanas inteligentes. Cuando el VO2 se deposita sobre sustratos de zafiro da lugar a efectos termocrómicos considerables; así, su transmitancia en el infrarrojo cambia en un 60 % después de la transición de fase del dióxido de vanadio, teniendo una dependencia menor con el espesor que la transmitancia en el ultravioleta. El efecto de aditivos sobre estas películas de dioxido de vanadio da lugar a una disminución de la temperatura de dicha transición responsable del efecto termocrómico, de manera que se produce a 30°C con el 1,5 % de adición de Mo
Experimental Verification of the Gapless Point in the =1 Antiferromagnetic Bond Alternating Chain
Susceptibility and high field magnetization measurements have been performed
on powder samples of an =1 bond alternating chain compound
[\{Ni(333-tet)(-N)\}](ClO) (333-tet=tetraamine
N,N'-bis(3-aminopropyl)-1,3-propanediamine). As the temperature is decreased,
the susceptibility exhibits a round maximum at around 120 K and decreases
gradually down to 10 K, and then falls down rapidly with a logarithmic
curvature which is behavior of the susceptibility of a gapless or a nearly
gapless antiferromagnetic chain. Magnetization up to 50 T at 1.4 K shows no or
a very small gap in this compound. We have carried out numerical calculations
for the =1 antiferromagnetic bond alternating chain with various alternating
ratios and obtained a very good agreement between experiments and
calculations for =0.6. We verify experimentally that the gapless point
exists around =0.6.Comment: 12 pages, 4 Postscript figures, uses REVTE
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