Question

A material loses its strong magnetization suddenly at a critical temperature and becomes weakly magnetic. This transition is from

• A. Diamagnetic $\to$ Paramagnetic
• B. Paramagnetic $\to$ Ferromagnetic
• C. Ferromagnetic $\to$ Paramagnetic
• D. Superconducting $\to$ Diamagnetic

Hint:

The Curie temperature of iron is approximately $770^\circ\text{C}$ ($1043\text{ K}$).
Above this temperature, iron is no longer attracted to a permanent magnet.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question explores the relationship between temperature and the magnetic structure of materials.
It tests the knowledge of thermal effects on the parallel alignment of atomic spins in strongly magnetic substances.

Step 2: Key Formula or Approach:
The transition temperature is known as the Curie temperature ($T_C$).
For temperatures above $T_C$, the susceptibility ($\chi$) of the material is described by the Curie-Weiss Law:
\[ \chi = \frac{C}{T - \theta_p} \] Where:
$C$ is the Curie constant.
$T$ is the absolute temperature.
$\theta_p$ is the paramagnetic Curie temperature.

Step 3: Detailed Explanation:

• Below the Curie temperature ($T < T_C$), a ferromagnetic material possesses spontaneous parallel spin alignment, leading to strong magnetic properties.

• As temperature increases, the randomizing thermal energy of atomic vibrations increases.

• When the temperature reaches and exceeds the Curie temperature ($T_C$), thermal agitation becomes strong enough to completely overcome the quantum mechanical exchange forces responsible for the spin alignment.

• Consequently, the magnetic domains are disrupted, the atomic dipoles become randomly oriented, and the material becomes weakly magnetic.

• This randomized, weakly magnetic state is characteristic of a paramagnetic material.

• Thus, heating past the Curie temperature causes a transition from Ferromagnetic $\to$ Paramagnetic.

Step 4: Final Answer:
The transition described is from Ferromagnetic to Paramagnetic, which matches option (C).