849 research outputs found
Effective field theory analysis of 3D random field Ising model on isometric lattices
Ising model with quenched random magnetic fields is examined for single
Gaussian, bimodal and double Gaussian random field distributions by introducing
an effective field approximation that takes into account the correlations
between different spins that emerge when expanding the identities. Random field
distribution shape dependencies of the phase diagrams and magnetization curves
are investigated for simple cubic, body centered and face centered cubic
lattices. The conditions for the occurrence of reentrant behavior and
tricritical points on the system are also discussed in detail.Comment: 13 pages, 8 figure
Inhomogeneous Ferromagnetism and Unconventional Charge Dynamics in Disordered Double Exchange Magnets
We solve the double exchange model in the presence of arbitrary
substitutional disorder by using a self consistently generated effective
Hamiltonian for the spin degrees of freedom. The magnetic properties are
studied through classical Monte Carlo while the effective exchange, ,
are calculated by solving the disordered fermion problem, and renormalised
self-consistently with increasing temperature. We present exact results on the
conductivity, magnetoresistance, optical response and `real space' structure of
the inhomogeneous ferromagnetic state, and compare our results with charge
dynamics in disordered La_{1-x}Sr_xMnO_3. The large sizes, ,
accessible within our method allows a complete, controlled calculation on the
disordered strongly interacting problem.Comment: 4 pages, 2 column revtex, 5 embedded figure
Effects of the randomly distributed magnetic field on the phase diagrams of the Ising Nanowire I: discrete distributions
The effect of the random magnetic field distribution on the phase diagrams
and ground state magnetizations of the Ising nanowire is investigated with
effective field theory with correlations. Trimodal distribution chosen as a
random magnetic field distribution. The variation of the phase diagrams with
that distribution parameters obtained and some interesting results found such
as reentrant behavior. Also for the trimodal distribution, ground state
magnetizations for different distribution parameters determined which can be
regarded as separate partially ordered phases of the system.Comment: 15 pages, 8 figure
Correlation equalities and upper bounds for the transverse Ising model
Starting from an exact formal identity for the two-state transverse Ising
model and using correlation inequalities rigorous upper bounds for the critical
temperature and the critical transverse field are obtained which improve
effective results.Comment: 8 pages, 1 figur
Multicritical Points And Reentrant Phenomenon In The BEG Model
The Blume - Emery - Griffiths model is investigated by use of the cluster
variation method in the pair approximation. We determine the regions of the
phase space where reentrant phenomenon takes place. Two regions are found,
depending on the sign of the reduced quadrupole - quadrupole coupling strength
. For negative we find Para-Ferro-Para and Ferro-Para-Ferro-Para
transition sequences; for positive , a Para-Ferro-Para sequence.
Order parameters, correlation functions and specific heat are given in some
typical cases. By-products of this work are the equations for the critical and
tricritical lines.Comment: 14 pages, figures available upon reques
Critical behavior and phase diagrams of a spin-1 Blume-Capel model with random crystal field interactions: An effective field theory analysis
A spin-1 Blume-Capel model with dilute and random crystal fields is examined
for honeycomb and square lattices by introducing an effective-field
approximation that takes into account the correlations between different spins
that emerge when expanding the identities. For dilute crystal fields, we have
given a detailed exploration of the global phase diagrams of the system in
plane with the second and first order transitions, as well
as tricritical points. We have also investigated the effect of the random
crystal field distribution characterized by two crystal field parameters
and on the phase diagrams of the system. The system exhibits
clear distinctions in qualitative manner with coordination number for
random crystal fields with . We have also found that,
under certain conditions, the system may exhibit a number of interesting and
unusual phenomena, such as reentrant behavior of first and second order, as
well as a double reentrance with three successive phase transitions.Comment: 19 pages, 17 figure
Nonequilibrium phase transitions and stationary state solutions of a three-dimensional random-field Ising model under a time dependent periodic external field
Nonequilibrium behavior and dynamic phase transition properties of a kinetic
Ising model under the influence of periodically oscillating random-fields have
been analyzed within the framework of effective field theory (EFT) based on a
decoupling approximation (DA). Dynamic equation of motion has been solved for a
simple cubic lattice () by utilizing a Glauber type stochastic process.
Amplitude of the sinusoidally oscillating magnetic field is randomly
distributed on the lattice sites according to bimodal and trimodal distribution
functions. For a bimodal type of amplitude distribution, it is found in the
high frequency regime that the dynamic phase diagrams of the system in
temperature versus field amplitude plane resemble the corresponding phase
diagrams of pure kinetic Ising model. Our numerical results indicate that for a
bimodal distribution, both in the low and high frequency regimes, the dynamic
phase diagrams always exhibit a coexistence region in which the stationary
state (ferro or para) of the system is completely dependent on the initial
conditions whereas for a trimodal distribution, coexistence region disappears
depending on the values of system parameters.Comment: 11 pages, 11 figure
Hysteretic response characteristics and dynamic phase transition via site dilution in the kinetic Ising model
The decay of the hysteresis loop area of the system, which is obeying a site
diluted kinetic Ising model, is considered by the disorder parameter using the
effective field theory analysis. The exhibition focuses on the understanding of
external field frequency, amplitude and the site concentration dependency of
the hysteresis loop area for several powerful treatments. Important
characteristics of the hysteretic response, such as frequency dispersion,
effect of domain nucleation phenomenon on the dynamic process etc. has been
introduced together with well known other characteristics. An attempt has been
made to explain the relations between the competing time scales (intrinsic
microscopic relaxation time of the system and the time period of the external
oscillatory field) and the shape of the response. As a result of the detailed
investigations, existence of essentially three, particularly four types of
dispersion curves have been propounded.Comment: 16 pages, 8 figure
Use of 3D imaging for providing insights into high-order structure of mitotic chromosomes
The high-order structure of metaphase chromosomes remains still under investigation, especially the 30-nm structure that is still controversial. Advanced 3D imaging has provided useful information for our understanding of this detailed structure. It is evident that new technologies together with improved sample preparations and image analyses should be adequately combined. This mini review highlights 3D imaging used for chromosome analysis so far with future imaging directions also highlighted
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