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Bragg-Williams microcanonical esemble
In this question Bragg-Williams theory of phase transition of the forum someone was asking for Bragg-Williams aprox. and how to calculate entropy. The answer is clear and correct, the Bragg-Williams ...
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Analytic methods for studying thin films (approximately 2D spin systems)
I am working on a project involving thin films of a magnetic material represented by essentially an Ising model on a 3 dimensional lattice. The bulk case is relatively straight forward, the ...
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The Ising approximation - what exactly is it?
I am slightly confused about the nature of the Ising model to study ferromagnetism. Consider the Heisenberg Hamiltonian with Zeeman term:
\[H=-\frac{1}{2} \sum_{i\ne j}J_{ij} S_i\cdot S_j+g\mu_B {B}\...
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Validity of Ising model for mean field thoery
The Heisenberg model for the Hamiltonian of a ferromagnet is given by:
$$H=-\frac{J}{2} \sum \vec{S}_i\cdot \vec{S}_j+\mu_B B \sum_i S^z_i$$
when performing mean field theory, to find $\chi$, we ...