How do ferromagnetism arise ?

Explanation

In ferromagnetic substances in solid state the metal ions in such substances are grouped together into small regions called domains. Each domain acts as a tiny magnet. In an unmagnetised piece of a ferromagnetic substance, these domains are randomly oriented in such a manner that their magnetic moments get cancelled. When such a substance is placed in a magnetic field, all the domains get oriented in the direction of the magnetic field field and a strong magnetic field is produced. This ordering of domains persist even when the magnetic field is removed and the ferromagnetic substances becomes a permanent magnet.