Quantum Mechanics/ Ferromagnitism

[bdrosd]

I'm hoping some one out there has as conceptual explanation as to the origin of Ferromagnetism. I know the magnetic fields are produced by moving charges and that atoms have moving electrons and hence display paramagnetism. Just a few pure elements have the ability to produce a permanent magnetic field, due to the cooperative alignment of the atomic magnetic moments. This is about where my understanding runs out of gas. Most sources I read simply say that the explanation for why certain substances produce this effect is "quantum mechanical in nature". I was hoping someone could give a little meaning to that last sentence.

 

[cesiumfrog]

I guess they're probably referring to the way in which the shape of the electron orbitals (and the "spin") can produce a magnetic moment. Figuring out which elements (which orbitals) this occurs in is QM, but the rest I think is just thermodynamics: if an atom is capable of sustaining a magnetic dipole in either direction, and the atom is in a slightly lower energy state when that dipole aligns with the external magnetic field, then all of the atoms would tend to align uniformly, except that at normal temperatures the disordered state is statistically favoured..