Question

Curie temperature is the temperature above which
A. A ferromagnetic material becomes paramagnetic
B. A paramagnetic material becomes diamagnetic
C. A ferromagnetic material becomes diamagnetic
D. A paramagnetic material becomes ferromagnetic

Answer 1

Hint:
Above Curie temperature, the magnetic dipole moments which are aligned in the same direction are free to arrange themselves in any direction. After they get oriented in a random direction, the property of that material which earlier had aligned dipole moment changes.

Complete answer:
The temperature above which certain materials lose their magnetic properties permanently and hence get replaced by induced magnetism is known as Curie Temperature. The materials remain to be magnetic below this temperature. Curie temperature is denoted by $ { T }_{ C }$. It is also referred to as the Curie point.

When the temperature is increased, the orientation of the magnetic dipole moments changes, and they get oriented in random directions. Thus, ferromagnetic material loses its magnetic property and starts showing paramagnetic properties. Few examples of ferromagnetic materials are iron, cobalt, nickel, etc. When the temperature is increased, the susceptibility of ferromagnetic material gets decreased.

Paramagnetic materials already have randomly oriented magnetic moments. It’s property remains the same at any temperature. Thus, this phenomenon is not seen in paramagnetic materials i.e. it does not have Curie temperature. Few examples of paramagnetic materials are Aluminium, oxygen, titanium, etc.

So, the correct answer is “Option A”.

Note:
Ferromagnetic materials are the material having opposite dipole moments. These dipoles have the same magnitude. When these materials are heated above their Curie temperature, they too lose their property and become paramagnetic. Thus, above Curie temperature, ferrimagnetic materials turn paramagnetic. This property is seen in antiferromagnetic materials too.