Materials having the properties of the magnet are magnetic materials. The magnetic materials can be classified into the following three types:
Paramagnetic materials
These materials have small but positive relative permeability i.e. nearly unity but greater than unity. These are ordinarily the non-magnetic materials like Cu, Al, etc. In such materials the individual atomic dipoles are oriented in the random fashion. On the application of the magnetising force the dipoles orient themself but not appreciably.
Diamagnetic material
The materials which have small and negative relative permeability but very nearly equal to unity. In this material the permanent magnetic dipoles are absent even nearly negligible. If the magnetising force is applied the magnetism is in opposite direction, thus the relative permeability is negative. This makes diamagnetic materials unimportant for electrical engineering applications.
Ferro-magnetic material
The magnetic materials in which the permeability varies considerably high and positive. It varies from 200 to 1000. The substance shows magnetic properties strongly high when subjected to a magnetic force. These materials are generally crystalline solid. The permanent magnetic atomic dipoles are aligned parallel to each Other and even a small amount of magnetising force causes a considerable change in the magnetism.