What is the temperature for the phase transition in the triangular-lattice Ising model? and in the hexagonal-lattice Ising model?

## 1 Answer

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I presume this is for a ferromagnetic interaction with all bonds of strength $J$.

The critical temperatures can be found using Kramers-Wannier duality and a star-triangle transformation. According to these notes they are $4J/\log(3)$ for the triangular and $2J/\log(2+\sqrt{3})$ for the hexagonal lattice.