…due to a phenomenon called electron exchange. As discussed above, a fundamental rule of quantum mechanics, the Pauli exclusion principle, states that no two electrons with the same direction of spin can occupy the same point in space at the same time. Electrons have charge and repel one another. If…

The exchange interaction between ions in this case has the opposite sign and favours the alternate arrangements of spins. The sign of the exchange interaction between ions depends on the length of the covalent bond and the bonding angles; it may have either orientation. The characteristic…

…mechanical effect known as the exchange interaction, is involved. A highly simplified description of how the exchange interaction aligns electrons in ferromagnetic materials is given here.