What is Magnetic Material ?
The materials which get magnetized in the presence of magnetic field is called Magnetic materials.
Non Magnetic materials get magnetized in presence of magnetic field but they exhibit weak magnetization.
Classification of Magnetic Materials
On the basis of magnetic behaviour, material may be classified as
- Diamagnetic
- Paramagnetic
- Ferromagnetic
Diamagnetic materials
It is a weak form of magnetism that is non-persistent and persists only when an external field is applied. Due to an applied magnetic field a change is occur in the orbital motor of electrons, due to this change a magnetic moment is induced in this materials.
The magnitude of induced magnetic moment is extremely small and in a direction opposite to that of applied magnetic field.
Diamagnetic materials are repelled by magnetic field.
Some of the materials that exhibit diamagnetism are Cu, Au, Ge, Si, Diamond, Al2O3, NaCl etc.
Paramagnetic Materials
When Paramagnetic Materials placed in a magnetic field its acquire a weak magnetization in the same direction as applied field.
In some materials, permanent magnetic dipole moments of the atoms or ions are acted upon individually, with no mutual interaction upon them, (randomly distributed), this effect is called Paramagnetism.
The total dipole moment in this material and hence magnetization is zero, in absence of external field.
In the presence of magnetic field, dipoles align in the direction of field.
But in absence of field due to thermal agitation dipoles are randomly oriented.
Paramagnetic materials are attracted by external field so it moves from low intensity to high intensity of the field.
Ferromagnetic Materials
Ferromagnetism is characterized by presence of parallel alignment of permanent magnetic dipole moments in a single direction.
Examples:- Fe, Cu, Ni, Gd & Dy
Ferromagnetic materials are spontaneously magnetized even in absence of external magnetic field.
All ferromagnetic materials behave as paramagnetic materials above Curie temperature.
The ferromagnetic properties of transition elements Fe, Co, Ni are due to spin of unpaired electrons. In Fe, Co & Ni, the unpaired 3d shell e- are responsible for ferromagnetism.
When a ferromagnetic material is subjected to an external field, it follows path OA of the magnetization curve.
When magnetic field is removed, some magnetization is still in the material called as residual magnetization having remnant flux density (Br).
To reduce residual magnetization to zero, external field needs to be applied in reverse direction called as Corecive Force (Hc).
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