Ferromagnetic substances are those which develop strong magnetization in the direction of the magnetizing field. They are strongly attracted by magnets and tend to move from weaker to stronger parts of a magnetic field.
Fig. (a) Randomly oriented domain (b) Aligned domains in a ferromagnetic substances
Properties of Ferromagnetic substances:
Ferromagnetic substances are those in which each atom or molecule has a strong spontaneous net magnetic moment. These substances exhibit strong paramagnetic properties:
- The susceptibility and relative permeability are very large. (For example : ?r for iron = 200,000)
- Susceptibility is inversely proportional to the absolute temperature. (i.e.) χm α 1/T. As the temperature increases the value of susceptibility decreases. At a particular temperature, ferromagnetic becomes paramagnetic. This transition temperature is called Curie temperature. For example Curie temperature of iron is about 1000 K.
- When suspended freely in uniform magnetic field, they set themselves parallel to the direction of magnetic field.
- When placed in a non uniform magnetic field, they have a tendency to move from the weaker part to the stronger part of the field. They get strongly magnetized in the direction of the field. Examples : Fe, Ni, Co and a number of their alloys.