CLASSIFICATION OF MAGNETIC MATERIALS
Depending upon the magnetic response, materials are classified into five types.
They are (i) Diamagnetic materials (ii) Paramagnetic materials (iii) Ferromagnetic materials (iv) Anti-ferro magnetic materials (v) Ferri magnetic materials
(i) Diamagnetic materials.
In diamagnetic materials, all the atoms will have random orientations of magnetic moments in the absence of magnetic field. In the presence of magnetic field, all the magnetic moments of its atoms will align in the opposite direction. Hence, the magnetic lines of force of the applied field cannot penetrate through it. So, relative permeability (μr) is < 1 and relative susceptibility (χr ) is low, negative. It is independent of temperature.
Ex: all organic materials
(ii) Paramagnetic materials:
In the absence of a magnetic field, all atoms in the paramagnetic material will have random orientations and do not exhibit net magnetic moment. When external magnetic field is applied, then all the magnetic moments align in the direction of applied field. So the magnetic lines of force pass through it. Hence their relative permeability (μr) is >1 and susceptibility (χr ) is low and positive.
Ex: Alkali metals, transition metals.
(iii) Ferromagnetic materials:
In ferromagnetic materials, the magnetic moments are predominantly due to spin magnetic moments of electrons, which will be aligned parallel to each other. If a ferromagnetic materials placed in a external magnetic field then magnetic moments align in its field direction exhibiting large net magnetic moments. So, the magnetic lines of force pass through the material. So, magnetic permeability (μr) is >>1 and susceptibility (χr ) is high and positive. The ferromag netism depends upon the temperature.
Ex: Transition and rare earth metals.
(iv) Anti-ferro magnetic materials:
The materials with anti-parallel magnetic moments are known as anti-ferromagnetic materials. The net magnetic moments exist in the direction of applied magnetic field. When external magnetic field is applied then the magnetic lines of force pass through it. Their permeability and susceptibility are low and positive.
Ex: salts of transition metals
(v) Ferrimagnetic materials:
The net magnetic moments exist in the direction of applied field. So, there exists large Induced magnetism exists in the direction of applied field. It allows large magnetic lines of force through them. Their permeability and susceptibility are high and positive.
***