Main Question or Discussion Point
One question? Neel temperature is temperature in which magnetisation is equal to zero?
What do you mean by sigma=0? If you mean that the entropy is zero, I don't think so. It holds when all the local moments are 'fully' aligned(such that two nearest neighbors point in opposite directions). At the Neel temperature, such alignment starts to develop.Can I say for [tex]\sigma=0[/tex], [tex]T=T_N[/tex]?