Explain the following with suitable examples:
Ferromagnetism.

Ferromagnetism: few substances like iron, cobalt, nickel, gadolinium and CrO₂ are strongly attracted by a magnetic field. Such substances are known as ferromagnetic substances. These substances can be permanently magnetised with the help of strong electrostatic field.  The metal ions of ferromagnetic substances are grouped together into small regions called domains in solid state. So that each domain acts as a tiny magnet. The domains of  un magnetized piece of a ferromagnetic are randomly oriented so that their magnetic moments get cancelled out. When such substance is placed in a magnetic field, all the domains get oriented in the direction of the magnetic field  and a strong magnetic effect is produced. This ordering of domains remains same  even when the magnetic field is removed and the ferromagnetic substance becomes a permanent magnet.