To distinguish between Hard and Soft ferromagnets: "Soft" materials (like soft iron) have high permeability but narrow hysteresis loops. "Hard" materials (like Alnico or Steel) have broad loops and high retentivity, making them ideal for permanent magnets.
Concept:
Magnetic materials are classified based on their response to external magnetic fields and their ability to retain magnetization.
• Diamagnetic: Weakly repelled by fields (e.g., Water, Copper, Bismuth).
• Paramagnetic: Weakly attracted by fields; lose magnetism when the field is removed (e.g., Sodium, Aluminum, Oxygen).
• Ferromagnetic: Strongly attracted; can be "Soft" (lose magnetism easily, like Soft Iron) or "Hard" (retain magnetism, like Alnico or Steel).
Step 1: Analyze the given pairs.
- (A) Diamagnetic - Gadolinium: Incorrect. Gadolinium is a rare-earth metal that is ferromagnetic at low temperatures and paramagnetic at room temperature.
- (B) Soft ferromagnetic - Alnico: Incorrect. Alnico is an alloy used for permanent magnets; it is a Hard ferromagnetic material.
- (C) Hard ferromagnetic - Copper: Incorrect. Copper is a classic example of a Diamagnetic material.
- (E) Permanent magnet - Aluminum: Incorrect. Aluminum is Paramagnetic and cannot retain permanent magnetism.
Step 2: Confirm the correct pair.
- (D) Paramagnetic - Sodium: This is correct. Sodium atoms have an unpaired electron in their outer shell, leading to a weak attraction to external magnetic fields typical of paramagnetic substances.
