I am somewhat confused about this topic.
It is usually explained how magnetic fields avoid break*ing* time reversal symmetry by the example of a field produced by a circulating charge current - run time backwards, the current direction is reversed and so is the field.
But what about the moment associated with the electron spin? Is the spin of an electron not an intrinsic property? So why (if indeed it does) would running time backwards change the sign of the spin?
EDIT: I appreciate all of your comments below, but I feel this question has got away from me somewhat. I should have added more information at first.
I am wondering about Anderson's description of a dirty superconductor where the pairing is between so-called time-reversed states. In Tinkham it says that these states are only degenerate in the absence of magnetic or other time-reversal noninvariant terms. This makes the previous edit (now in italics) a little confusing to me.
Back to the loop of current: Surely if you switch the charge and the direction of flow then the magnetic field stays pointing in the same direction. Where is the inconsistency here?