Substances like iron, cobalt, nickel, gadolinium and CrO₂, are known as the ferromagnetic substances and make better permanent magnets as they are attracted very strongly by the magnetic field. These substances can also be permanently magnetized. The metal ions of ferromagnetic substances, in solid-state are grouped into small regions, which are known as domains. Each domain act as a tiny magnet. Meanwhile, in an magnetized piece of a ferromagnetic substance, the domains are randomly oriented and so the magnetic moments of the domains get cancelled. Nevertheless, when the substance is placed in a magnetic field, all the domains are oriented in the direction of the magnetic field and produces a strong magnetic effect. The ordering of the domains persists even after the removal of the magnetic field. Thus, the ferromagnetic substance becomes a permanent magnet.