Diamagnetic Effect

DIAMAGNETIC EFFECT

Diamagnetism is exhibited by all the materials.

The atoms in diamagnetic materials do not possess permanent magnetic moments.

However, when the diamagnetic material is placed in an external magnetic field, the electrons in the atomic orbits tend to counteract the external magnetic field. Hence, the atoms acquire an induced magnetic moment.

As a result, the material becomes magnetised. The direction of the induced dipole moment is opposite to that of externally applied magnetic field.

Due to this effect, the material is very weakly repelled in magnetic field. This phenomenon is known as diamagnetism.

We can understand diamagnetism by the schematic illustration in fig 2.23 (a) and (b).

When the magnetic field H is zero, the atoms possess zero magnetic moment (fig 2.23 (a)).

When a magnetic field Ho is applied in the direction shown (fig 2.23 (b)), the atoms acquire an induced magnetic moment in the direction opposite to that of the magnetic field.

(a) Diamagnetic material. The atoms do not possess magnetic moment.

(b) When a magnetic field H。 is applied, the atoms acquire induced magnetic moment in the direction opposite to the applied field resulting in negative susceptibility

The strength of the induced magnetic moment is proportional to the applied field and hence the magnetisation of the material varies directly with the strength of the magnetic field.

The induced dipoles and magnetization vanish as soon as the applied magnetic field is removed.

The susceptibility of the diamagnetic material is negative. Due to this, the material is weakly repelled in the magnetic field.

Diamagnetic materials

The materials which exhibit diamagnetism are called diamagnetic materials.

Properties

(i) The diamagnetic materials repel the magnetic lines of force. The behaviour of a perfect diamagnetic material in the presence of magnetic field is shown in fig. 2.24.

(ii) There is no permanent dipole moment. Therefore, the magnetic effects are very small in these materials.

(iii) The magnetic susceptibility is negative and it does not depend on temperature and applied magnetic field strength.

Example: Gold, germanium and silicon.