What are ferromagnetic substances? Give three properties of ferromagnetic substances. Explain the domain theory of ferromagnetism using diagram.
Ferromagnetic substances are those which gets strongly magnetized when placed in an external magnetic field.
Properties
i. They have a strong tendency to move from a region of water magnetic field to a strong magnetic field, i.e., they get strongly attracted to a magnet.
ii. In the nonuniform magnetic field, the sample tends to move towards the region of the high field.
iii. The ferromagnetic property depends on temperature. At high enough temperature, a ferromagnet becomes a paramagnet. The domain structure disintegrates with temperature.
(a) Randomly oriented domains
(b) Aligned domains
The individual atoms in a ferromagnetic material possess a dipole moment as in a paramagnetic material, However, they interact with one another in such a way that they spontaneously align themselves in a common direction over a macroscopic volume called domain.
Each domain has a net magnetization. In the first instant, the magnetization varies randomly from domain to domain and there is no bulk magnetization as shown in Fig (a). When we apply an external magnetic field B0, the domains orient themselves in the direction of B0 and simultaneously the domain oriented in the direction of B0 grow in size. Fig (b) shows the situation when the domains have aligned and amalgamated to form a single ‘gaint’ domain.
