Materials for making permanent magnet should possess high residual magnetism i.e., when the magnetising field is reduced to zero, the intensity of magnetisation is high. Further, to reduce the residual magnetism to zero, the magnetising field should be applied in the opposite direction. The greater this value, the magnetisation will be a long lasting one. This property of the magnet is called coercivity.
Examples of such substance are steel and alnico (alloy of Al, Ni, Co).
It is for this reason, that steel in spite of its low residual magnetism has a high coercivity and so is preferred for making permanent magnet.
