Question

What is the effect of temperature on magnetic susceptibility of ferromagnetic materials?

• A. increases with increasing temperature.
• B. remains unchanged with increasing temperature.
• C. decreases with increasing temperature.
• D. Sometimes increases and sometimes decreases depending on the environment.

Hint:

Think of temperature as a randomizing force for magnetism. For ordered magnetic states like ferromagnetism, increasing temperature always leads to more disorder, thus reducing the magnetic properties like susceptibility and spontaneous magnetization.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Ferromagnetism is characterized by a strong alignment of atomic magnetic moments due to quantum mechanical exchange interactions. This alignment is opposed by thermal agitation. The magnetic susceptibility (\(\chi\)) is a measure of how strongly a material becomes magnetized in an external magnetic field.
Step 2: Detailed Explanation:
As the temperature of a ferromagnetic material increases, the thermal energy causes increased random vibrations of the atoms. This thermal agitation works against the exchange forces, disrupting the long-range ordering of the magnetic domains. This leads to a decrease in the overall magnetization and hence a decrease in magnetic susceptibility.
This effect becomes very pronounced as the temperature approaches the Curie temperature (\(T_C\)). At \(T_C\), the thermal energy becomes strong enough to completely overcome the exchange forces, and the material undergoes a phase transition from ferromagnetic to paramagnetic. Above the Curie temperature, the material is paramagnetic, and its susceptibility continues to decrease with increasing temperature according to the Curie-Weiss law, \(\chi = C/(T - T_C)\).
Step 3: Final Answer:
Therefore, for a ferromagnetic material, the magnetic susceptibility consistently decreases as the temperature increases.