Two Dimensions
- In the ferromagnetic case there is a phase transition: at low temperature, Peierls argument proves positive magnetization for the nearest neighbor case and then, by Griffiths inequality, also when longer range interactions are added; while, at high temperature, cluster expansion gives analyticity of the thermodynamic functions.
- In the nearest-neighbor case, the free energy has been exactly computed by Onsager, through the equivalence of the model with free fermions on lattice. The spin-spin correlation functions has been computed by McCoy and Wu.
Read more about this topic: Ising Model
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