Subject: What is exchange coupling in ferromagnets?

I'm trying to understand the difference between diamagnets, paramagnets, and 
ferromagnets.  I understand the different characteristics, but I'm having a 
hard time understanding the forces behind them.  

For diamagnetic characteristics to be predominant, a material must have no 
unpaired electrons.  When this material is placed in a magnetic field, it seems 
as though the field would try to force half of the electrons to spontaneously 
flip their spin, but the other electron in any given orbital won't allow this, 
so the two are pushing against each other.  Is this correct?

Paramagnets make sense.

Ferromagnets sort of make sense...but I can't find any specific information on 
exchange coupling anywhere on this site (or really anywhere else online either) 
and how exchange coupling causes large numbers of atoms/electrons to work 
together.  One thing I read mentioned in passing that this is because electric 
interaction between electrons in a ferromagnet push them into a state of having 
similar spins, and this electric push overcomes any quantum push to have 
opposing spins.  I think I'm really mixed up on that part...any help would be 
appreciated.  Please include any extra reading materials that would be 
helpful.  Thanks. 

Re: What is exchange coupling in ferromagnets?