I read many different explanation but none of them is satisfying. There is two cases: 1. I move an iron rod in a magnetic field, between two bar magnet for example. To this case I read that when I move the rod the electrons on it also move and moving charges produce magnetic field which interact with the external B field. I think this is impossible because those electrons don't move locally just relatively. This cannot produce net magnetic field arround the rod just allign the spin of the electrons. Maybe this B field interact with the external one? 2. Iron core of a transformer transfer the energy. In this case electrons in the secondary winding don't move at all. Allign to the external B field but just due to its spin magnetic moment. Just the spin allign and e- doesn't move at all. What causes the charge separation?