Paramagnetic Effect

PARAMAGNETIC EFFECT

In certain materials, each atom or molecule possesses a net permanent magnetic moment (due to orbital and spin magnetic moments) even in the absence of an external magnetic field.

The magnetic moments are randomly oriented in the absence of an external magnetic field as shown in fig. 2.25(a). This makes the net magnetic moment zero and hence the magnetisation of the material is zero.

But, when an external magnetic field is applied, the magnetic dipoles tend to align themselves in the direction of the magnetic field as shown in fig. 2.25(b) and the material becomes magnetized.

This effect is known as paramagnetism.

With an increase in temperature, increase in thermal agitation disturbs the alignment of the magnetic moments.

It tends to randomize the dipole direction thus leading to decrease in magnetization.

 (a) Each atom possesses a permanent magnetic moment. When H=0, all the magnetic moments are randomly oriented so M = 0.

(b)When a magnetic field H₀ is applied, the magnetic moments tend to orient themselves in the direction of the field, resulting in positive susceptibility

This indicates that the paramagnetic susceptibility decreases with increase in temperature. It is noted that the paramagnetic susceptibility varies inversely with temperature.

Χ∞1/ T

χ  = C/T

This is known as Curie's law of paramagnetism. C is a constant which is called as Curie's constant.

Paramagnetic materials

The magnetic materials which exhibit paramagnetism are called as paramagnetic material.

Properties

(i) The paramagnetic materials attract the magnetic lines of force.

(ii) They possess permanent dipole moment.

(iii) The value of susceptibility is positive and it depends on temperature. It is given by

Χ = C / T- θ

(iv) The spin alignment is shown in fig 2.26.

Example: Manganous sulphate, ferric oxide, ferrous sulphate and nickel sulphate