Rare Earth Magnets
1. What Are Rare Earth Magnets?
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Permanent magnets made from rare-earth element alloys.
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Discovered in the 1960s–1980s (Yttrium-Cobalt alloy, Neodymium-Iron-Boron by Dr. Masato Sagawa).
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Much stronger than regular (ceramic or alnico) magnets.
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Used where high strength, compact size, or weight constraints are critical.
2. Types of Rare Earth Magnets:
| Type | Features | Applications |
|---|---|---|
| Neodymium (NdFeB) | - Strongest, most affordable - Susceptible to rust and temperature | Audio devices, printers, DC motors, medical tools |
| Samarium Cobalt (SmCo) | - Highly stable at high/cryogenic temps - More brittle, corrosion-resistant | Aerospace, satellites, sensors, magnetic couplings |
3. Comparison: Neodymium vs Samarium Cobalt
| Feature | NdFeB | SmCo |
|---|---|---|
| Strength | Higher magnetic strength | Lower than NdFeB |
| Cost | More affordable | More expensive |
| Temperature sensitivity | Sensitive to heat | Stable at high temperatures |
| Corrosion resistance | Needs protective coating | Naturally corrosion-resistant |
| Brittleness | Less brittle | More prone to chipping |
4. Rare Earth Magnets vs Regular (Ceramic/Ferrite) Magnets
| Feature | Rare Earth Magnets | Regular Magnets (Ferrite/Ceramic) |
|---|---|---|
| Strength | 2–7x stronger | Much weaker |
| Composition | Rare earth alloys (Nd, Sm) | Mostly iron oxide (Ferrite) |
| Size for strength | Small size, high power | Larger size for same strength |
| Demagnetisation | High resistance | Easier to demagnetise |
| Cost | More expensive | Cheaper |
| Temperature resistance | Limited for NdFeB, high for SmCo | Better thermal stability |
5. Key Technical Details:
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Remanence: Exceeds 1.2 Tesla in rare earth magnets.
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Curie Temperature (NdFeB): ~310°C — beyond which they lose magnetism.
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Protection: Coated with nickel or stainless steel to prevent corrosion.
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Applications: Electronics, EVs, medical devices, aerospace, defence systems.
6. Disadvantages of Rare Earth Magnets:
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Susceptible to corrosion (especially NdFeB).
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Temperature limitations in standard grades.
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Brittle nature, especially in SmCo, requiring careful handling.
UPSC Mains Relevance:
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Science & Tech: Applications in defence, EVs, renewable energy.
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Economy: Strategic importance due to dependence on imports (mainly from China).
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Environment & Industry: Mining of rare earths and impact on indigenous capability (e.g., India’s ₹5000 crore rare earth scheme).