In 1907 A.D., Weiss proposed domain theory to explain ferromagnetic phenomenon in material. According to this theory, a single crystal of ferromagnetic solid comprises large number of small regions, and each region is spontaneously magnetized to saturation extent called a domain as shown in Fig.2 (a). The size of domain may vary from 10−6 to the whole volume of the crystal. The spin magnetic moments of entire atoms confined within a domain are oriented in a particular direction. The directions of magnetizations of different domains of the specimen are random so that the resultant of magnetizations of all domains in the material is zero in the absence of an applied magnetic field. These domains arise because the energy is not minimum when a large specimen has a uniform magnetization. When external magnetic field is applied, these domains align in the direction of applied field and specimen shows net magnetization and becomes magnet as shown in Fig. 2 (b).
In simple way, domains are regions of magnetic substances that have a free, spinning electron. When these domains line up, the substance becomes a magnet.
(a) Magnetic material in demagnetised condition: Atomic magnets in alignment inside domains but domain magnetic axes in random directions.
(b) Magnetised state: Atomic magnets turn to bring domain magnetic axes in direction of magnetising field
Fig. 2: Magnetic domain in ferromagnetic substance.
Also see (Click on these quick links) :
1. Domain Theory of Ferromagnetism: http://www.askmattrab.com/notes/93-domain-theory-of-ferromagnetism
2. Antiferromagnetic and Ferrimagnet: http://www.askmattrab.com/notes/94-antiferromagnet-and-ferrimagnet
3. Magnetic Materials: http://www.askmattrab.com/notes/95-magnetic-materials
4. Working of the Transformer: http://www.askmattrab.com/notes/97-working-of-the-transformer