22 April 2011

Differences between Ferro, Ferri and Antiferro magnetic materials

Ferromagnetic Materials
Antiferro magnetic Materials
Ferrimagnetic Materials
All the magnetic dipoles are aligned parallel and oriented in the same direction.
This parallel alignment of atomic magnetic dipoles occurs only in microscopic regions called magnetic domains.
Here the successive magnetic dipoles are aligned in opposite directions.
Here the successive magnetic moments are of different magnitude and are aligned in opposite direction.
The net magnetization is zero, if the domains are randomly oriented.
At room temperature, manganese and chromium in the solid state exhibit antiferromagnetism. The ratio of a/d for Mn and Cr is less than 1.4 and they have a negative exchange energy.
A large magnetization is produced on applying a small magnetic field.

The magnetic dipoles of Fe, Co and Ni are arranged parallel due to the creation of positive exchange energy between them. The ratio of atomic spacing to the diameter of the 3d orbit is in the range of 1.4 to 2.7 for Fe, Co and Ni for which this parallel alignment occurs whereas for manganese and chromium a/d does not fall in this range. Hence Mn and Cr are not ferromagnetic.
Susceptibility is very small and positive. The susceptibility increases with increasing temperature and reaches a maximum value at one particular temperature called as Neel temperature. Above the Neel temperature, the antiferro magnetic material becomes a paramagnetic material.
They are used in high frequency applications.
When ferromagnetic materials are heated, it loses its magnetism slowly.
Examples: Ferrous oxide, Manganese oxide, Zinc ferrite.
Example: Ferrous ferrite, Nickel ferrite, Manganese ferrite.