Explain the following terms with suitable examples :
(i) Schottky defect
(ii) Ferromagnetism.

Explanation

(1) The substances which possess unpaired electrons and high paramagnetic character and when placed in a magnetic field are strongly attracted and show permanent magnetic moment even when the external magnetic field is removed are said to be ferromagnetic.
They can be permanently magnetised.
(2) In the solid state, the metal ions of ferromagnetic substance are grouped together into small regions called domains, where each domain acts as a tiny magnet.

For example : `Fe, Co, Gd, CrO_(2),` etc.