Magnetic materials and retentivity Materials with low retentivity (low remanent magnetization after removal of the magnetizing field) are most suitable for which application?

Introduction / Context:
Retentivity (remanence) measures how much magnetization a material retains after the external magnetic field is removed. Design choices for magnetic devices hinge on whether you want the field to persist or to vanish quickly.

Given Data / Assumptions:

• Low retentivity implies the B–H loop has small remanent flux density.
• Coercivity may also be low for soft magnetic materials.
• Applications considered: electromagnets, relays, permanent magnets, and recording media.

Concept / Approach:
Soft magnetic materials (e.g., low-carbon steel, silicon steel) have low retentivity and low coercivity. They magnetize easily and, crucially, demagnetize readily when the field is removed—ideal for devices that must switch on and off with the applied current.

Step-by-Step Solution:
Identify requirement for electromagnets/relays: high permeability and minimal residual magnetism to avoid sticking.Low retentivity satisfies this requirement.Permanent magnets require high retentivity and high coercivity (hard magnetic materials), which is the opposite.Therefore, low-retentivity materials are suited to temporary magnets.

Verification / Alternative check:
B–H curves of soft steels show narrow hysteresis loops and small remanence, matching the operational needs of transformers and relay cores.

Why Other Options Are Wrong:
Weak permanent magnets: Still need adequate remanence; low retentivity gives poor performance and instability. High-performance permanent magnets: Demand very high retentivity (e.g., NdFeB). Both equally: Contradictory properties cannot satisfy both.

Common Pitfalls:
Confusing high permeability (desirable in soft magnets) with high retentivity (desirable in hard magnets).

Final Answer:
Temporary magnets such as electromagnet cores and relay armatures