Explain the following with suitable examples:
$(i)$ Ferromagnetism

(N/A) $(i)$ Ferromagnetism: The substances that are strongly attracted by a magnetic field are called ferromagnetic substances.
Ferromagnetic substances can be permanently magnetised even in the absence of a magnetic field.
Some examples of ferromagnetic substances are iron,cobalt,nickel,gadolinium,and $CrO_2$.
In solid state,the metal ions of ferromagnetic substances are grouped together into small regions called domains and each domain acts as a tiny magnet.
In an unmagnetised piece of a ferromagnetic substance,the domains are randomly-oriented and so,their magnetic moments get cancelled.
However,when the substance is placed in a magnetic field,all the domains get oriented in the direction of the magnetic field.
As a result,a strong magnetic effect is produced.
This ordering of domains persists even after the removal of the magnetic field.
Thus,the ferromagnetic substance becomes a permanent magnet.
Schematic alignment of magnetic moments in ferromagnetic substances: