In statistical physics, the classical Heisenberg model, developed by Werner Heisenberg, is the case of the n-vector model, one of the models used to model ferromagnetism and other phenomena.
The classical Heisenberg model can be formulated as follows: take a d-dimensional lattice, and place a set of spins of unit length,
on each lattice node.
The model is defined through the following Hamiltonian:
where
is a coupling between spins.
Independently of the range of the interaction, at a low enough temperature the magnetization is positive.
Conjecturally, in each of the low temperature extremal states the truncated correlations decay algebraically.