ferromagnetic
interaction This interaction makes two spins – small magnets carried by the electrons to two neighbouring atoms – to align. Were the spins not parallel, the electrons would be able to coexist in one same atom, but this would be at great cost because two electrons repulse each other electrically. To avoid this additional cost, the electrons choose to have parallel spins, so that they can profit from the exclusion principle.
you will find this interaction in this storie: