Properties of Ferromagnetic Materials
Ferromagnetic materials also belong to the paramagnetic family. But the values of magnetic permeability are many times more and the magnetic attraction is very strong. In these materials, magnetic moments of the paramagnetic atoms or ions remain locked in a large area or region.
Ferromagnetic materials show the following properties:
(i) If a ferromagnetic material is placed in a uniform non-magnetic field it moves rapidly froth the lower field strength region to higher field strength region. It is strongly attracted.
(ii) When a ferromagnetic material is placed in a magnetic field, its lines of force are distorted markedly.
(iii) Magnetic induction B of a ferromagnetic material is very high compared to the magnetic field intensity H.
(iv) Magnetic susceptibility K of a ferromagnetic material is positive and of very high value.
(v) Both the permeability and the susceptibility of this magnetic material are changed along with the magnetic field intensity.
With the increase of temperature magnetic susceptibility (K) of ferromagnetic materials continues to decrease.
Both the magnetic permeability and susceptibility of this material change with magnetic field intensity. If the temperature is raised above critical value the exchange interaction disappears suddenly and the material changes into a paramagnetic material. This critical temperature is called the Curie temperature. For iron, this temperature is 1043 K.
There are two more materials in the class of ferromagnetism. These are called antiferromagnetic and ferrimagnetic materials.