I've been told in my solid state class, that ferromagnetism occurs when electron spins are alligned. This happens, as I understand it, when it is "energitically favorable" and when the wavefunction is antisymmetric (with a symmetric spin part). What I don't understand is:
1) When the spin part is symmetric and the electrons are alligned, the Coloumb repulsion is minimized (due to the Pauli principle, the electrons move further apart) - should it not always be more energitically favorable for the spins to be alligned?
2) Why, for instance, is iron (Fe) ferromagnetic, while Manganese (Mn) is paramagnetic? I fail to see where the theory comes into play. By looking at their orbital structure, Mn has more unpaired valence electrons than Fe.