I know that the ferromagnetism of iron is because of its unpaired d electrons, but I also know that there are other metals with unpaired electrons like aluminum that are not ferromagnetic. Is the difference due to the molecular orbitals or whatever the name is for the orbitals in a solid metal? I have a suspicion but I'm not sure that in bulk aluminum, the lone unpaired electron of one aluminum somehow shares a molecular(?) orbital with another aluminum atom with a lone electron of the opposite spin so that the net result is that there are no unpaired electrons.
I think this based on a calculation I read in a very well-regarded physics book by Purcell. In the book he calculates the magnetic dipole moment of a magnet that he doesn't identify except to say that it is a new type of magnet that can be formed into a disc, and since Purcell came out in the 1960's, I suspect he is referring to the ferrite ceramic magnets. In his calculation, he seems to use one unpaired electron per "molecule".
If the ferrite magnets do have one unpaired electron per "molecule", in contrast to the iron atom in textbooks having 4 unpaired electrons, I'm suspecting that some of the spins are being cancelled out in the actual magnet, and thus I suspect that something similar is happening in aluminum. Is this correct?