Question

Magnetic susceptibility $\chi$ of a paramagnetic material changes with absolute temperature $T$ as

• A. $\chi \propto T^{-1}$
• B. $\chi =constant$
• C. $\chi \propto e^T$
• D. $\chi \propto T$

Answer 1

The correct option is A $\chi \propto T^{-1}$

Each atom has a magnetic moment which is randomly oriented as a result of thermal agitation. The application of a magnetic field creates a slight alignment of these moments and hence a low magnetisation in the same direction as the applied field. As the temperature increases, then the thermal agitation increases and it becomes harder to align the atomic magnetic moments and hence the susceptibility will decrease.

This behaviour is known as the Curie law ${\chi }_m=\frac{C}{T}$

where, C is a material constant called the Curie constant.