90,394 research outputs found
Takahashi Integral Equation and High-Temperature Expansion of the Heisenberg Chain
Recently a new integral equation describing the thermodynamics of the 1D
Heisenberg model was discovered by Takahashi. Using the integral equation we
have succeeded in obtaining the high temperature expansion of the specific heat
and the magnetic susceptibility up to O((J/T)^{100}). This is much higher than
those obtained so far by the standard methods such as the linked-cluster
algorithm. Our results will be useful to examine various approximation methods
to extrapolate the high temperature expansion to the low temperature region.Comment: 5 pages, 4 figures, 2 table
Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors
Applying the dynamical coherent potential approximation to a simple model, we
have systematically studied the carrier states in Mn-type diluted
magnetic semiconductors (DMS's). The model calculation was performed for three
typical cases of DMS's: The cases with strong and moderate exchange
interactions in the absence of nonmagnetic potentials, and the case with strong
attractive nonmagnetic potentials in addition to moderate exchange interaction.
When the exchange interaction is sufficiently strong, magnetic impurity bands
split from the host band. Carriers in the magnetic impurity band mainly stay at
magnetic sites, and coupling between the carrier spin and the localized spin is
very strong. The hopping of the carriers among the magnetic sites causes
ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have
investigated the condition for the DE-like mechanism to operate in DMS's. The
result reveals that the nonmagnetic attractive potential at the magnetic site
assists the formation of the magnetic impurity band and makes the DE-like
mechanism operative by substantially enhancing the effect of the exchange
interaction. Using conventional parameters we have studied the carrier states
in GaMnAs. The result shows that the ferromagnetism is caused
through the DE-like mechanism by the carriers in the bandtail originating from
the impurity states.Comment: 20 pages, 14 figure
Thermodynamical Bethe Ansatz and Condensed Matter
The basics of the thermodynamic Bethe ansatz equation are given. The simplest
case is repulsive delta function bosons, the thermodynamic equation contains
only one unknown function. We also treat the XXX model with spin 1/2 and the
XXZ model and the XYZ model. This method is very useful for the investigation
of the low temperature thermodynamics of solvable systems.Comment: 52 pages, 6 figures, latex, lamuphys.st
The Free Energy and the Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field
A nonlinear susceptibilities (the third derivative of a magnetization
by a magnetic field ) of the =1/2 ferromagnetic Heisenberg chain and the
classical Heisenberg chain are calculated at low temperatures In both
chains the nonlinear susceptibilities diverge as and a linear
susceptibilities diverge as The arbitrary spin Heisenberg
ferromagnet has a scaling relation between and
The scaling function
=(2/3)-(44/135) + O() is common to all values of spin
Comment: 16 pages (revtex 2.0) + 6 PS figures upon reques
Integrable Magnetic Model of Two Chains Coupled by Four-Body Interactions
An exact solution for an XXZ chain with four-body interactions is obtained
and its phase diagram is determined. The model can be reduced to two chains
coupled by four-body interactions, and it is shown that the ground state of the
two-chain model is magnetized in part. Furthermore, a twisted four-body
correlation function of the anti-ferromagnetic Heisenberg chain is obtained.Comment: 7 pages, LaTeX, to be published in J. Phys. Soc. Jpn., rederived the
mode
Magnetic Resonant X-Ray Scattering in KCuF3
We study the magnetic resonant x-ray scattering (RXS) spectra around the
edge of Cu in KCuF on the basis of an {\em ab initio} calculation. We use
the full-potential linearlized augmented plane wave method in the LDA
scheme, and introduce the lattice distortion as inputs of the calculation.
We obtain finite intensity on magnetic superlattice spots, about three orders
of magnitude smaller than on orbital superlattice spots, by taking account of
the spin-orbit interaction (SOI). No intensity appears without the SOI,
indicating that the intensity arises not from the spin polarization but from
the orbital polarization in states. The present calculation reproduces
well the experimental spectra as functions of photon energy and of azimuthal
angle. We also calculate the RXS intensity on orbital superlattice spots. It is
found that the intensity increases with increasing Jahn-Teller distortion. The
spectra remain nearly the same in the nonmagnetic state given by the simple
LDA, in which the orbital polarization in the 3d states is much smaller. This
strongly suggests that the intensity on orbital spots is mainly controlled by
the lattice distortion, not by the 3d orbital order itself.Comment: 7 pages, 8 figures, Submitted to PRB, RevTeX
On the location of two blow up points on an annulus for the mean field equation
We consider the mean field equation on two-dimensional annular domains, and
prove that if and are two blow up points of a blowing-up solution
sequence of the equation, then we must have .Comment: To appear in CRA
Modified Spin Wave Analysis of Low Temperature Properties of Spin-1/2 Frustrated Ferromagnetic Ladder
Low temperature properties of the spin-1/2 frustrated ladder with
ferromagnetic rungs and legs, and two different antiferromagnetic next nearest
neighbor interaction are investigated using the modified spin wave
approximation in the region with ferromagnetic ground state. The temperature
dependence of the magnetic susceptibility and magnetic structure factors is
calculated. The results are consistent with the numerical exact diagonalization
results in the intermediate temperature range. Below this temperature range,
the finite size effect is significant in the numerical diagonalization results,
while the modified spin wave approximation gives more reliable results. The low
temperature properties near the limit of the stability of the ferromagnetic
ground state are also discussed.Comment: 9 pages, 8 figure
Universal low-temperature properties of quantum and classical ferromagnetic chains
We identify the critical theory controlling the universal, low temperature,
macroscopic properties of both quantum and classical ferromagnetic chains. The
theory is the quantum mechanics of a single rotor. The mapping leads to an
efficient method for computing scaling functions to high accuracy.Comment: 4 pages, 2 tables and 3 Postscript figure
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