What is the difference between ferromagnetic and paramagnetic substances ?

Explanation

Substances like `Fe,Co,Ni,CrO_(2)` etc. attracted very strongly by magnetic fields. Such substances are called ferromagnetic substances. Such substances have domain structure.
Substances like `O_(2),Cu^(2+),Fe^(3+),Cr^(3+)` etc. weakly attracted by a magnetic fields. These are called paramagnetic substances. They have one or more unpaired electrons.