7.7 Domain theory of ferromagnetism
In 1907, Weiss proposed domain theory to explain ferromagnetism. According to this theory, a single crystal of ferromagnetic solid compresses a large number of small regions, and each region is spontaneously magnetized to saturation extent called a domain as shown in Fig. 7.6. The domain size may vary from 10−6 to the entire volume of the crystal. The spin magnetic moments of all the atoms in a domain are oriented in a particular direction. The magnetization directions of different domains of the specimen are random so that the resultant magnetization of the material is zero in the absence of an external magnetic field. These domains arise because the energy is not minimum when a large specimen has a uniform ...
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