Ferromagnetism materials

FERROMAGNETIC MATERIALS

In a ferromagnetic material the number of unpaired electrons are more. Most of these spin magnetic moments point in one direction as shown in Fig. 1.9.

Hence even in the absence of external field, the magnetic moments align themselves parallel to each other and give rise to magnetic field.

Effect of magnetic field

To these materials even if a small external magnetic field is applied, the magnetic moments which are already aligned parallel, reorient itself along the direction of the magnetic field and they become very strong magnets.

Properties

1. Since some magnetisation is already existing in these materials, all the magnetic lines of force passes through it (Fig. 1.10).

2. They have permanent dipole moment. So they act as strong magnets.

3. They exhibit magnetisation even in the absence of external field. This property is called Spontaneous magnetisation.

4. It's susceptibility is positive and high and it is given by

χ= C / T‒θ

5. When the temperature is greater than curie temperature, ferromagnetic material becomes paramagnetic material.

6. Permeability is very much greater than 1.

Examples: Ni, Co, Fe etc.,