1,037 research outputs found
EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC
The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis
Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets
It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and
main text. Final accepted versio
The antiferromagnetic order in an F-AF random alternating quantum spin chain : (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3
A possibility of the uniform antiferromagnetic order is pointed out in an
S=1/2 ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg
quantum spin chain compound: (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3. The system
possesses the bond alternation of strong random bonds that take +/- 2J and weak
uniform AF bonds of -J. In the pure concentration limits, the model reduces to
the AF-AF alternation chain at x=0 and to the F-AF alternation chain at x=1.
The nonequilibrium relaxation of large-scale quantum Monte Carlo simulations
exhibits critical behaviors of the uniform AF order in the intermediate
concentration region, which explains the experimental observation of the
magnetic phase transition. The present results suggest that the uniform AF
order may survive even in the presence of the randomly located ferromagnetic
bonds.Comment: 4 pages, 3 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
Quantum Monte Carlo Study on Magnetization Processes
A quantum Monte Carlo method combining update of the loop algorithm with the
global flip of the world line is proposed as an efficient method to study the
magnetization process in an external field, which has been difficult because of
inefficiency of the update of the total magnetization. The method is
demonstrated in the one dimensional antiferromagnetic Heisenberg model and the
trimer model. We attempted various other Monte Carlo algorithms to study
systems in the external field and compared their efficiency.Comment: 5 pages, 9 figures; added references for section 1, corrected typo
Excitation Spectrum of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain:
The natural explanation of the excitation spectrum of the spin-1
antiferromagnetic Heisenberg chain is given from the viewpoint of the spin-1/2
ferromagnetic-antiferromagnetic alternating Heisenberg chain. The energy
spectrum of the latter is calculated with fixed momentum by numerical
diagonalization of finite size systems. It consists of a branch of propagating
triplet pair (triplet wave) and the continuum of multiple triplet waves for
weak ferromagnetic coupling. As the ferromagnetic coupling increases, the
triplet wave branch is absorbed in the continuum for small , reproducing the
characteristics of the spin-1 antiferromagnetic Heisenberg chain.Comment: 12 Pages REVTEX, Postscript file for the figures included.
SKPH-94-C00
Effects of Single-site Anisotropy on Mixed Diamond Chains with Spins 1 and 1/2
Effects of single-site anisotropy on mixed diamond chains with spins 1 and
1/2 are investigated in the ground states and at finite temperatures. There are
phases where the ground state is a spin cluster solid, i.e., an array of
uncorrelated spin-1 clusters separated by singlet dimers. The ground state is
nonmagnetic for the easy-plane anisotropy, while it is paramagnetic for the
easy-axis anisotropy. Also, there are the N\'eel, Haldane, and large-
phases, where the ground state is a single spin cluster of infinite size and
the system is equivalent to the spin-1 Heisenberg chain with alternating
anisotropy. The longitudinal and transverse susceptibilities and entropy are
calculated at finite temperatures in the spin-cluster-solid phases. Their
low-temperature behaviors are sensitive to anisotropy.Comment: 8 pages, 4 figure
Phase diagram and hidden order for generalized spin ladders
We investigate the phase diagram of antiferromagnetic spin ladders with
additional exchange interactions on diagonal bonds by variational and numerical
methods. These generalized spin ladders interpolate smoothly between the
chain with competing nn and nnn interactions, the chain with
alternating exchange and the antiferromagnetic chain. The Majumdar-Ghosh
ground states are formulated as matrix product states and are shown to exhibit
the same type of hidden order as the af chain. Generalized matrix product
states are used for a variational calculation of the ground state energy and
the spin and string correlation functions. Numerical (Lanczos) calculations of
the energies of the ground state and of the low-lying excited states are
performed, and compare reasonably with the variational approach. Our results
support the hypothesis that the dimer and Majumdar-Ghosh points are in the same
phase as the af chain.Comment: 23 pages, REVTEX, 7 figure
Ground State and Elementary Excitations of the S=1 Kagome Heisenberg Antiferromagnet
Low energy spectrum of the S=1 kagom\'e Heisenberg antiferromagnet (KHAF) is
studied by means of exact diagonalization and the cluster expansion. The
magnitude of the energy gap of the magnetic excitation is consistent with the
recent experimental observation for \mpynn. In contrast to the KHAF,
the non-magnetic excitations have finite energy gap comparable to the magnetic
excitation. As a physical picture of the ground state, the hexagon singlet
solid state is proposed and verified by variational analysis.Comment: 5 pages, 7 eps figures, 2 tables, Fig. 4 correcte
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