Classification of magnetic materials:-
Magnetic materials for which linear relationship between M and H exists are divided into classes depending upon the sign of χ (magnetic susceptibility). Materials, which have negative value of χ the order of 10-4 to 10-6 are called diamagnetic and those which have a positive value of χ of about the same order of magnitude are called paramagnetic. When the relationship between M and H is non-linear and exhibits hysterises effect, this group of materials in which the resultant magnetization is one to several orders of magnitude. Such materials are called Ferromagnetic materials.
Another classification of magnetic materials consists in the presence or absence of permanent magnetic dipolar in them, Materials, which lack permanent magnetic dipoles, are called diamagnetic. If permanent magnetic dipoles are present in the atoms of a material, it may be paramagnetic, ferromagnetic, anti- ferromagnetic of ferrimagnetic depending on the interaction between the individual dipoles. Thus, if the interact between the atomic permanent dipoles moments is zero or negligible and the individual dipole moments are oriented at random as shown in fig (i).
The material will be paramagnetic. If the dipole interact in such a manner that they tend to line up in parallel, as shown in fig (ii), the material will be ferromagnetic. When neighboring moments are aligned anti parallel as shown in fig (iii), the materials are anti- ferromagnetic. In ferromagnetic materials, there is a large resultant magnetization, whereas in anti-ferromagnetic materials the magnetisation vanishes. When the order of the magnetic moments is as shown in fig (iv), the phenomena is known as ferrimagnetisms.
Examples of diamagnetic materials are Diamonds, Graphite and copper etc. Examples of paramagnetic materials are Aluminium , Ebonite & platinum etc. Examples of Ferromagnetic materials are Iron, cobalt and Nickel etc.