Magnetic materials are classified into three categories, based on the behaviour of materials in the magnetic field. The three types of materials are diamagnetic, paramagnetic and ferromagnetic.
Diamagnetic substances when placed in an external magnetic field produce negative magnetization. Therefore, diamagnetic substances are repelled by magnets. Paramagnetic substances acquire a small net magnetic moment in the direction of the applied field. Therefore, they are slightly attracted by the magnetic field.
Ferromagnetic materials are strongly attracted by the magnetic field. These materials retain the magnetism even when the magnetic field is removed. This lagging of magnetization of a ferromagnetic substance behind the magnetic field is called Hysteresis.
5 Magnetic Properties of Materials
Property 1: Intensity of magnetisation (I)
The electrons circulating around the nucleus have a magnetic moment. When the material is not magnetised the magnetic dipole moment sum up to zero. When the material is kept in an external magnetic field, the magnetic moments are aligned in a particular direction and the material gets a net non-zero dipole moment. The net dipole moment per unit volume is defined as magnetization or intensity of magnetisation.
Property 2: Magnetic Field (H) or Magnetic intensity
The magnetic field produced only by the electric current flowing in a solenoid is called the magnetic intensity. It is the external magnetic field that induces magnetic property in a material.
Property 3: Magnetic susceptibility
When a material is placed in an external magnetic field, the material gets magnetised. For a small magnetising field, the intensity of magnetisation (I) acquired by the material is directly proportional to the magnetic field (H).
I ∝ H
I = χmH , χm is the susceptibility of the material.
Property 4: Retentivity
The ability of a material to retain or resist magnetization is called retentivity.
Property 5: Coercivity
The coercivity of a material is the ability to withstand the external magnetic field without becoming demagnetised.