scholarly journals Hysteresis in Two-Dimensional Liquid Crystal Models

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Slavko Buček ◽  
Samo Kralj ◽  
T. J. Sluckin
Keyword(s):  
External Field ◽  
Numerical Study ◽  
Mean Field ◽  
Hysteresis Loops ◽  
Two Dimensional ◽  
Zero Temperature ◽  
Coupling Constant ◽  
Field Approach ◽  
Random Anisotropy ◽  
Internal Coupling

We make a numerical study of hysteresis loop shapes within a generalized two-dimensional Random Anisotropy Nematic (RAN) model at zero temperature. The hysteresis loops appear on cycling a static external ordering field. Ordering in these systems is history dependent and involves interplay between the internal coupling constantJ, the anisotropy random fieldD, and the ordering external fieldH. Here the external field is represented by a traceless tensor, analogous to extension-type fields in continuum mechanics. The calculations use both a mean field approach and full lattice simulations. Our analysis suggests the existence of two qualitatively different solutions, which we denote assymmetricandsymmetry breaking. For the set of parameters explored, only the symmetric solutions are stable. Both approaches yield qualitatively similar hysteresis curves, which are manifested either by single or double loops. But the quantitative differences indicate that mean field estimates are only of limited predictive value.

FAILURE OF A MEAN-FIELD APPROACH FOR THE MILLER–HUSE PHASE TRANSITION

2000 ◽  
Vol 10 (01) ◽  
pp. 251-256 ◽  
Author(s):  
FRANCISCO SASTRE ◽  
GABRIEL PÉREZ
Keyword(s):  
Phase Transition ◽  
Ising Model ◽  
Chaotic Maps ◽  
Initial Conditions ◽  
Mean Field ◽  
Region Of Interest ◽  
Universality Class ◽  
Two Dimensional ◽  
Field Approach

The diffusively coupled lattice of odd-symmetric chaotic maps introduced by Miller and Huse undergoes a continuous ordering phase transition, belonging to a universality class close but not identical to that of the two-dimensional Ising model. Here we consider a natural mean-field approach for this model, and find that it does not have a well-defined phase transition. We show how this is due to the coexistence of two attractors in its mean-field description, for the region of interest in the coupling. The behavior of the model in this limit then becomes dependent on initial conditions, as can be seen in direct simulations.

FIELD-THEORETICAL CALCULATIONS ON THE HALDANE GAP OF QUASI-ONE-DIMENSIONAL HEISENBERG ANTIFERROMAGNETS

2009 ◽  
Vol 23 (31) ◽  
pp. 5789-5800
Author(s):  
HAI HUANG
Keyword(s):  
Finite Temperature ◽  
Theoretical Calculations ◽  
Mean Field ◽  
Zero Temperature ◽  
Ginzburg Landau ◽  
One Dimensional ◽  
Field Approach ◽  
Haldane Gap ◽  
Chain Theory ◽  
Heisenberg Antiferromagnets

One-dimensional Heisenberg antiferromagnets can be described by the O (3) nonlinear σ-model (NLσM). We give a review on zero temperature and finite temperature Haldane gaps obtained from this model. Based on the coupled-chain theory, we derive the finite temperature Haldane gap for triangular antiferromagnet RbNiCl 3. The Néel temperature is obtained as 11 K. In order to treat the anisotropy in crystal Ni ( C 2 H 8 N 2)2 NO 2( ClO 4), we relax the constraint of the NLσM and compute the finite temperature Haldane gap using a Ginzburg–Landau mean field approach. The comparison with the experimental data is discussed.

Static and Dynamic Properties of a Two-Dimensional Charged Bose Fluid

1998 ◽  
Vol 12 (12) ◽  
pp. 459-465 ◽  
Author(s):  
E. Strepparola ◽  
M. P. Tosi
Keyword(s):  
Coulomb Potential ◽  
Ground State ◽  
Coupling Strength ◽  
Dynamic Properties ◽  
Complete Solution ◽  
Mean Field ◽  
Strongly Correlated ◽  
Two Dimensional ◽  
Large Coupling ◽  
Field Approach

A complete solution of the Singwi–Tosi–Land–Sjölander approximation is given for the ground state and the elementary excitations of a fluid of charged bosons interacting via the two-dimensional ln (r) Coulomb potential at arbitrarily large coupling strength r s . The results are used to discuss the limitations of a static-mean-field approach in such a strongly correlated system.

scholarly journals Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 800
Author(s):  
Joscha Detzmeier ◽  
Kevin Königer ◽  
Tomasz Blachowicz ◽  
Andrea Ehrmann
Keyword(s):  
Magnetization Reversal ◽  
Thermal Effects ◽  
Hysteresis Loops ◽  
Ferromagnetic Nanoparticles ◽  
Zero Temperature ◽  
Small Deviations ◽  
Micromagnetic Simulations ◽  
Random Anisotropy ◽  
Ferromagnetic Nanostructures ◽  
Biased Samples

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles.

ANYONIC SUPERCONDUCTIVITY WITH FERROMAGNETIC GROUND STATE

1992 ◽  
Vol 06 (22) ◽  
pp. 3513-3527 ◽  
Author(s):  
B. CHAKRABORTY ◽  
S. RAMASWAMY ◽  
V. RAVISHANKAR
Keyword(s):  
Ground State ◽  
Mean Field ◽  
Meissner Effect ◽  
Gauge Fields ◽  
Zero Temperature ◽  
Field Approach ◽  
Current Correlation ◽  
Self Consistent ◽  
Ferromagnetic Ground State ◽  
Chern Simons

We study a system of non-relativistic two-dimensional spin-1/2 fermions minimally coupled to Chern-Simons and Maxwell gauge fields, at zero temperature. A self-consistent mean field approach leads to a ferromagnetic ground state which nevertheless is also superconducting. We calculate the spin and current correlation functions and show that there is a Meissner effect for weak external magnetic fields, characterised by two penetration lengths. The dispersion relations for the two longitudinal excitations are given. Further, the system supports spin waves which are massless in the absence of electromagnetic fields.

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