Magnetism – domain theory and experimental evidence Assertion (A): Magnetic behavior of ferromagnets can be explained using the concept of magnetic domains. Reason (R): The existence of domains is demonstrated experimentally by Bitter powder (magnetic colloid) patterns that reveal domain walls.

Difficulty: Easy

Correct Answer: Both A and R are true and R is the correct explanation of A

Explanation:


Introduction / Context:
Ferromagnetic materials exhibit spontaneous magnetization due to aligned spins within microscopic regions called domains. Understanding domains explains hysteresis, coercivity, remanence, and how magnetization changes under applied fields via domain wall motion and rotation.


Given Data / Assumptions:

  • Ferromagnets minimize total energy by forming domains that reduce magnetostatic energy.
  • Domain walls separate regions with different magnetization directions.
  • Visualization techniques include Bitter patterns and modern magnetic force microscopy.


Concept / Approach:

Domain theory posits that a bulk specimen is partitioned into domains whose magnetizations are individually saturated but differently oriented. Upon applying a field, domains favorably oriented grow at the expense of others, and walls move, producing macroscopic magnetization changes. Bitter powder patterns use fine ferromagnetic particles or colloids that accumulate at stray-field regions near domain walls, making the domain structure visible and thereby providing direct evidence for domains.


Step-by-Step Solution:

Relate macroscopic magnetization curves to domain processes (wall motion then rotation).Explain why domains form: tradeoff among exchange, anisotropy, magnetostatic, and wall energies.Cite Bitter technique: particles align with local stray fields, highlighting walls and verifying the domain model.


Verification / Alternative check:

Modern techniques (Kerr microscopy, Lorentz TEM, MFM) confirm domain structures and dynamics, reinforcing the classical evidence from Bitter patterns.


Why Other Options Are Wrong:

(b) underplays the explanatory link; (c) R is not false; (d) A is not false.


Common Pitfalls:

Assuming individual atomic moments randomly reorient in isolation; in reality, collective domain processes dominate at low to moderate fields.


Final Answer:

Both A and R are true and R is the correct explanation of A

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