Why domains occur

Why domains occur

We saw in the previous chapter that quantum mechanics gives rise to an exchange energy which tends to align electron spins, and hence their magnetic dipole moments, parallel to each other. The exchange energy provides a strong driving force for parallel alignment therefore we might expect that ferromagnetic materials should be composed of one single domain, with all dipoles aligned in the same direction.

Although a single domain would certainly minimize the exchange contribution to the total energy, there are a number of other contributions to the total magnetic energy of a ferromagnet. The formation of domains allows a ferromagnetic material to minimize its total magnetic energy, of which the exchange energy is just one component. The other main contributors to the magnetic energy are the magnet static energy, which is the principal driving force for domain formation, and the magnet crystalline and magnetostrictive energies, which influence the shape and size of domains. Next we will discuss each of these energy contributions in turn, and show how they determine the formation and structure of domains in ferromagnetic materials.

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