Curie Temperature: Determining Critical Point & Lattice Changes

[dlesswater]

I was wondering how to we determine the Curie Temperature of a ferromagnet? I know an experiment can give us the critical point, but what about the changes in the lattice of each substance changes curie temperature? I do know it depends on the coordination number(number of neighbors). My teacher said something about the magnetic exchange interaction but I don't know what that is. Any help would be appreciated.

 

[asheg]

If you have 2 magnets beside each other which their positions are fixed they try to rotate so that one be opposite of the other.The temperature's role is like a random rotation force on these magnets. So when the temperature is high enough they don't behave correlated. When you have a lot of such magnets what happens? You should write the hamiltonian of the system considering the magnetic interaction between neighbors.