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Ferromagnetic Materials:- These are materials in which magnetic dipoles interact in such a manner that they tend to line up in parallel. A ferromagnetic substance consists of a number of regions or domains, which are spontaneously magnetized. The direction of magnetization varies from domain to domain. The resultant magnetization is zero or nearly zero. The relative permeability is very high. In presence of external magnetic field, the ferromagnetic materials get strongly magnetised and exhibit hysterisis loop. The susceptibility of these is given by χ = C / T − TC , where C is curie constant, TC is the curie temperature above which the ferromagnetic material exhibits paramagnetic behaviour. The ferromagnetic materials are widely used in industries. Ex. Iron, nickel, cobalt.
Paramagnetic Materials:- The atoms of these materials contain permanent magnetic dipoles. Individual dipoles are oriented in random fashion such that resultant magnetic field is zero or negligible. For these materials relative permeability is slightly greater than unity and it is independent of magnetizing force. In presence of external magnetic field, paramagnetic materials get weakly magnetised in the field direction and the susceptibility is given by χ = C / T , where C is a curie constant and T is the temperature. Ex. Chromium chloride, chromium oxide, manganese sulphate, air.
Diamagnetic Materials:- These are the materials whose atoms do not carry permanent magnetic dipoles. If an external magnetic field is applied to a diamagnetic material, it induces a magnetization in the direction opposite to the applied field intensity. For these materials the relative permeability is negative. These are hardly used as magnetic material in electrical/ electronic engineering applications. Ex. Aluminium oxide, copper, gold, barium chloride.
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