Question

What are hard magnetic materials?

Answer 1

Hint: Magnetism is the phenomenon due to which opposite magnetic poles attract and same magnetic poles repel. The magnetic materials are those which produce a magnetic field around them. Magnetic materials are either naturally occurring or artificially made. A hard magnetic material is a man-made magnet.

Complete answer:
A magnetic material is one which produces a magnetic field around it. Magnetic materials are either naturally magnetized or artificially magnetized by keeping in an external magnetic field. In order to magnetise a material, it is kept in a magnetic field which leads to the formation of magnetic dipole moments within it. When these dipole moments align in the same direction as the external magnetic field then the material gets magnetised.
Hard magnetic materials are those materials which are very difficult to magnetise but once they are magnetised, they become permanent magnets. Such materials have high retentivity as well as high coercive force. The area under the hysteresis loop is very high, nearly rectangle.
Some important properties of hard magnetic materials are-
Initial permeability is small
It has a high hysteresis loop
The area covered under the BH curve is large
High value of coercivity and retentivity
Therefore, hard magnetic materials are those which can get permanently magnetised.

Note:
Coercivity is the ability of a magnetic material to resist an external magnetic field without getting demagnetized. Retentivity is the magnetism retained by a material after the external magnetic field is removed. The other type of magnetic materials is soft magnetic materials.