A resource useful to meditate about spin alignment:http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/helium.html
the energy levels of para- and ortho-helium, that is, with spins anti- or parallel, one electron as 1s and the other as varied orbitals.
The energy differs much. The interaction of magnetic moments, about as weak as the orbital-spin interaction that defines the fine structure, can't possibly explain it.
Spin alignment changes the energy even when electrons are not on identically named orbitals. So spin alignment matters more than the mere exclusion principle.
Because electrons are fermions, their common wave function ψ(r1
) must be antisymmetric, including the comparison between spin1
. It's a mathematical consequence of being fermions, not a force. This implies that the (6-dimensional hyper-) shape ψ(r1
) differs whether the spins are anti- or parallel. Then the energy differs a lot, due to the proximity with the nucleus and between the electrons.
We use to represent parallel spins as "up", but I understand it only means "all parallel", and they could all be "down" equally well. It's not an interaction with the orbital angular momentum or magnetic field.