When engineers need a strong permanent magnet, the choice usually comes down to two rare-earth materials: neodymium iron boron (NdFeB) and samarium cobalt (SmCo). Both are far stronger than ferrite or alnico magnets, but they behave very differently under heat, moisture, and cost pressure. Choosing the wrong one can lead to lost performance, early failure, or unnecessary cost.
Here’s a practical comparison to help you decide.
Magnetic strength
NdFeB is the strongest permanent magnet material commercially available. Sintered NdFeB grades reach a maximum energy product of around 50 MGOe and above, while SmCo typically ranges from about 16 to 32 MGOe.
In practice, this means an NdFeB magnet can deliver the same magnetic force in a smaller, lighter size. That’s why NdFeB dominates compact designs such as smartphones, earphones, and EV motors.
Winner for strength: NdFeB
Temperature performance
This is where SmCo shines. Standard NdFeB grades are rated for about 80°C, and high-coercivity grades (SH, UH, EH, AH) extend this to around 150–230°C. Above that, NdFeB loses its magnetism quickly.
SmCo5 magnets work reliably up to about 250°C, and Sm2Co17 grades up to about 300–350°C. SmCo also has a much lower temperature coefficient, so its magnetic output changes less as temperature rises. For precision sensors and instruments, this stability can matter as much as the maximum temperature itself.
Winner for high temperature and stability: SmCo
Corrosion resistance
NdFeB contains a large amount of iron and corrodes easily in humid environments, so it almost always needs a protective coating such as nickel (Ni-Cu-Ni), zinc, or epoxy.
SmCo has excellent natural corrosion resistance and often needs no coating at all, which makes it a good choice for harsh, humid, or chemical environments.
Winner for corrosion resistance: SmCo
Mechanical properties
Both materials are hard and brittle, and both can chip or crack if handled roughly. SmCo is generally the more brittle of the two, which can make machining complex shapes more challenging. Good design practices, such as chamfered edges and avoiding thin sections, help with both materials.
Cost
NdFeB is usually significantly less expensive than SmCo, mainly because cobalt and samarium cost more than neodymium and iron. For high-volume products, this difference has a major impact on total cost.
Winner for cost: NdFeB
Quick comparison
| Property | NdFeB | SmCo |
|---|---|---|
| Magnetic strength | Very high (up to ~52 MGOe) | High (~16–32 MGOe) |
| Max working temperature | ~80–230°C, depending on grade | ~250–350°C, depending on grade |
| Temperature stability | Good | Excellent |
| Corrosion resistance | Needs coating | Excellent, usually uncoated |
| Brittleness | Brittle | More brittle |
| Cost | Lower | Higher |
How to choose
Choose NdFeB if:
- You need maximum strength in a small size
- Your working temperature stays below about 150–200°C
- Cost is an important factor
- Typical uses: EV motors, consumer electronics, speakers, sensors, and industrial motors
Choose SmCo if:
- Your application runs above about 200°C
- You need very stable output across a wide temperature range
- The magnet works in a corrosive environment without coating
- Typical uses: aerospace, high-temperature motors, precision sensors, and oil and gas tools
The middle ground: high-temperature NdFeB
Many designs fall between the two. If your application runs at 150–200°C, a high-coercivity NdFeB grade such as 38UH or 35EH may give you the heat resistance you need at a lower cost than SmCo. The right choice depends on your exact temperature, the magnet’s shape, and the demagnetizing forces in your design.
Frequently asked questions
Is SmCo stronger than NdFeB?
No. NdFeB is stronger at room temperature. However, at very high temperatures SmCo can outperform NdFeB, because NdFeB loses strength faster as it heats up.
Can NdFeB be used without a coating?
It’s not recommended. Uncoated NdFeB corrodes quickly in humid air. Choose a coating that suits your environment, such as Ni-Cu-Ni for general use or epoxy for humid conditions.
Which magnet is better for EV motors?
Most EV motors use high-coercivity NdFeB grades, because they offer the best combination of strength, temperature resistance, and cost.