Tricritical phenomena in an Ising model with nearest- and next-nearest-neighbor interactions

1977 ◽  
Vol 55 (13) ◽  
pp. 1125-1133 ◽  
Author(s):  
M. Plischke ◽  
D. Zobin
Keyword(s):  
Field Theory ◽  
High Temperature ◽  
Ising Model ◽  
Nearest Neighbor ◽  
Tricritical Point ◽  
Mean Field Theory ◽  
Mean Field ◽  
Temperature Series ◽  
Bcc Lattice ◽  
Ferromagnetic Interactions

We report on the analysis of low and high temperature series for the Ising model with nearest-neighbor antiferromagnetic and next-nearest-neighbor ferromagnetic interactions on the bcc lattice. The high temperature series are complete to β7, the low temperature series to u37. We determine the phase diagram, locate the tricritical point, and estimate the tricritical exponents. The tricritical exponents are only in fair agreement with the predictions of tricritical mean field theory.

Generation of low tehmperature series for Ising models with nearest and next nearest neighbor interactions

1976 ◽  
Vol 54 (16) ◽  
pp. 1646-1650 ◽  
Author(s):  
M. Plischke ◽  
C. F. S. Chan
Keyword(s):  
Low Temperature ◽  
Nearest Neighbor ◽  
Tricritical Point ◽  
Ising Models ◽  
Temperature Data ◽  
Temperature Series ◽  
Bcc Lattice ◽  
Special Cases ◽  
Ising Antiferromagnet ◽  
Ferromagnetic Interactions

We have generalized the code method of Sykes et al. and applied it to the Ising model with nearest and next nearest neighbor interactions. On the bcc lattice, we have obtained the first seven low temperature polynomials for arbitrary sign of the interactions. Special cases of this model are the Ising ferromagnet and the Ising antiferromagnet with next nearest neighbor ferromagnetic interactions. The latter system exhibits a tricritical point which we plan to study using our low temperature data and high temperature series to be obtained in the future.

Mean field theory of the orientational properties of (J = 1) hydrogen molecules on the surface of Grafoil

1979 ◽  
Vol 57 (11) ◽  
pp. 1852-1869 ◽  
Author(s):  
A. B. Harris ◽  
A. J. Berlinsky
Keyword(s):  
Field Theory ◽  
Model Comparison ◽  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Computer Calculation ◽  
Mean Field ◽  
Free Energy Calculations ◽  
Axially Symmetric ◽  
Hydrogen Molecules ◽  
Ordered Phases

A mean field theory is developed which is applicable to the orientational behavior of (J = 1) hydrogen molecules on the surface of Grafoil. The hydrogen molecules are assumed to form a triangular lattice in a weak, axially symmetric crystal field, Vc. perpendicular to the substrate and to interact via the electric quadrupole–quadrupole interaction with nearest-neighbor coupling constant Γ. Free energy calculations for the various possible ordered phases are presented, and a Landau expansion is used to investigate the phase boundary between the disordered and ordered phases. A computer calculation, based on the iterative method of James, is used to determine the lines of transition between ordered phases. For almost all values of Vc < 22.5Γ, the disordered to ordered state phase transition is continuous. Four distinct types of ordered phases are found — a four-sublattice phase, two two-sublattice phases, and a one-sublattice phase which resembles an X–Y model. Comparison is made to the recent nmr data of Kubik and Hardy for H2 and D2 on Grafoil.

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