Magnetic domain

Magnetic domains are regions within a material in which magnetic moments (the small permanent magnets that make up macroscopic magnets) are aligned. A magnetic domain can appear in a material in which there is a long-range magnetic ordering (ferromagnetic or ferrimagnetic, among others). They were discovered by Pierre Weiss, who realized, in 1907, that ferromagnetic materials are formed by these domains.

If the magnetic domains in a given material are oriented to the same pole, that material will not exhibit magnetic properties; Because like poles repel each other, while opposite poles attract. This allows us to explain why iron is not spontaneously ferromagnetic. This was proven by Barkhausen in 1919, who by means of electronic amplifiers heard the "clicks" when an external field forces the Weiss domains to align. This is an irreversible behavior that explains the phenomenon of hysteresis.

The domains are separated by the so-called domain walls, in which the transition in the orientation of the dipoles occurs. Above a certain critical temperature (Curie temperature), the magnetic domains become disordered and disappear due to entropy, giving rise to a paramagnetic system.

Under certain conditions (high fields, single crystals, small samples), a material can be composed of a single magnetic domain called a monodomain.

Scheme of magnetic domains of a ferromagnete aligning with a growing field