Question

Which of the following materials possesses anti-parallel spins of unequal magnitude, resulting in a spontaneous magnetic moment below a critical temperature?

• A. Ferromagnetic
• B. Paramagnetic
• C. Antiferromagnetic
• D. Ferrimagnetic

Hint:

The classic example of a ferrimagnetic material is Magnetite ($\text{Fe}_3\text{O}_4$).
It contains both $\text{Fe}^{2+}$ and $\text{Fe}^{3+}$ ions, which occupy different lattice sites with opposing, unequal magnetic moments.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the class of magnetic materials characterized by anti-parallel magnetic spins of unequal magnitude that yield a net spontaneous magnetization.

Step 2: Key Formula or Approach:
We analyze the orientation and magnitude of the atomic magnetic moments (spins) in different magnetic structures:
- Ferromagnetic: Parallel spins ($\uparrow \uparrow \uparrow \uparrow$).
- Antiferromagnetic: Anti-parallel spins of equal magnitude ($\uparrow \downarrow \uparrow \downarrow$), cancelling to zero.
- Ferrimagnetic: Anti-parallel spins of unequal magnitude ($\uparrow \Downarrow \uparrow \Downarrow$), leading to a net non-zero magnetic moment.

Step 3: Detailed Explanation:

• Ferrimagnetism: Occurs in materials (like magnetite, $\text{Fe}_3\text{O}_4$, and other ferrites) where the crystal lattice contains different sublattices with opposing magnetic moments.

• Because the opposing moments on the sublattices are unequal in magnitude, they do not completely cancel each other out.

• This incomplete cancellation results in a net spontaneous magnetic moment in the direction of the larger spins below a critical temperature (the Curie temperature).

• Unlike antiferromagnets, which have zero net magnetization, ferrimagnets exhibit strong macroscopic magnetic properties similar to ferromagnets, though they generally have lower saturation magnetization.

Step 4: Final Answer:
The materials are classified as Ferrimagnetic.