Schwinger-Boson approach to the two-dimensional antiferromagnetic Heisenberg model beyond the mean-field approximation

2000 ◽  
Vol 61 (5) ◽  
pp. 3508-3512 ◽  
Author(s):  
Feng Wang ◽  
Ruibao Tao
Keyword(s):  
Heisenberg Model ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Two Dimensional ◽  
The Mean ◽  
Antiferromagnetic Heisenberg Model

Critical indices for spin correlation functions in ferromagnetic films

1979 ◽  
Vol 57 (10) ◽  
pp. 1686-1698 ◽  
Author(s):  
G. Gumbs ◽  
A. Griffin
Keyword(s):  
Correlation Functions ◽  
Finite Thickness ◽  
Mean Field ◽  
Spin Correlation ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Dimensional System ◽  
Two Dimensional ◽  
Critical Indices ◽  
The Mean

Using the Ginzburg–Landau–Wilson (GLW) Hamiltonian, we obtain, with the mean-field approximation, explicit expressions for the spin–spin correlation function χ(z,z′) of a film of thickness L above the phase transition temperature Tc and the spontaneous magnetization [Formula: see text] below Tc. The boundaries are treated using a temperature-independent extrapolation length Λ. From our results, we verify explicitly that for finite L, the critical indices associated with the spin–spin correlation functions and the surface magnetization are identical with those for the analogous two-dimensional system, for both the ordinary (Λ > 0) and surface (Λ < 0) transitions. Our model results nicely exhibit the fact that as long as L is finite, when the temperature T approaches sufficiently close to Tc, there is a crossover from behaviour characteristic of a single surface to two-dimensional behaviour. Within the one-loop, Hartree self-consistent field approximation, we study the effects of mode–mode coupling on the surface layer susceptibility in films of varying thicknesses. The singular behaviour obtained in the mean-field approximation is found to be completely removed in systems of finite thickness, the susceptibilities only exhibiting a finite cusp at the transition.

scholarly journals Mean-field Solution of the mixed spin-1 and spin-5/2Ising system with different single-ion anisotropies

2009 ◽  
Vol 6 (4) ◽  
pp. 784-789
Author(s):  
Baghdad Science Journal
Keyword(s):  
Phase Diagram ◽  
Ground State ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Two Dimensional ◽  
Ground State Phase Diagram ◽  
Mixed Spin ◽  
Bogoliubov Inequality ◽  
The Mean

The mixed-spin ferrimagnetic Ising system consists of two-dimensional sublattices A and B with spin values and respectively .By used the mean-field approximation MFA of Ising model to find magnetism( ).In order to determined the best stabile magnetism , Gibbs free energy employ a variational method based on the Bogoliubov inequality .The ground-state (Phase diagram) structure of our system can easily be determined at , we find six phases with different spins values depend on the effect of a single-ion anisotropies .these lead to determined the second , first orders transition ,and the tricritical points as well as the compensation phenomenon .

Magnetic properties and phase diagrams of the mixed spin-(1 2, 3 2) Ising–Heisenberg model in the mean field approximation

2021 ◽  
pp. 2150486
Author(s):  
G. Seto ◽  
R. A. A. Yessoufou ◽  
A. Kpadonou ◽  
E. Albayrak ◽  
F. Hontinfinde
Keyword(s):  
Phase Diagrams ◽  
Heisenberg Model ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Quadrupole Moments ◽  
New Approach ◽  
Crystal Fields ◽  
Mixed Spin ◽  
The Mean

In this paper, the effects of the longitudinal [Formula: see text] and the transverse [Formula: see text] crystal fields on the mixed spin-[Formula: see text] Ising–Heisenberg model have been studied. The thermodynamic properties of the model are obtained by using a new approach of the mean field approximation (MFA). The thermal variations of the order-parameters and the total magnetic susceptibility of the model are carefully investigated to obtain the phase diagrams on the [Formula: see text] planes for [Formula: see text] and on the [Formula: see text] planes for [Formula: see text] and 6. The existence of compensation temperatures between the sublattice magnetizations, [Formula: see text], and the two components of the quadrupole moments, [Formula: see text], are observed. Our results are compared with other existing works in the literature and reliable agreements are found.

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