Four magnet families cover virtually every industrial application. They do not compete on a single axis — each one wins in a different operating window. Choosing between them is the first engineering decision of any magnetic design, and it is almost impossible to correct cheaply later.
The Four Families, Side by Side
| NdFeB | SmCo | Ferrite | AlNiCo | |
|---|---|---|---|---|
| Remanence Br | 1.0–1.47 T | 0.9–1.15 T | 0.2–0.45 T | 0.6–1.35 T |
| (BH)max | 33–53 MGOe | 16–32 MGOe | 3–5 MGOe | 5–12 MGOe |
| Max. operating temp | 80–200°C (grade-dependent) | 250–350°C | ≈ 250°C | 450–550°C |
| Corrosion resistance | Poor — coating required | Good | Excellent (oxide) | Excellent |
| Mechanical | Brittle | Very brittle | Brittle, hard | Best machinability of the four |
| Relative cost | $$–$$$$ | $$$$ | $ | $$$ |
| Typical uses | Motors, sensors, robotics, medical, holding | High-temp motors, aerospace, downhole, defense | DC motors, speakers, latching, separators | Instruments, sensors, high-temp holding |
Typical commercial ranges — grade-specific values on request.
When Each One Wins
NdFeB — when flux density rules
The strongest permanent magnet material ever commercialized. If your constraint is space or weight — a smaller motor, a thinner sensor package, a stronger latch in the same pocket — NdFeB is the default. Its weaknesses are temperature (see our grade guide) and corrosion (see the coating guide). Both are manageable when specified, fatal when ignored.
SmCo — when heat rules
Samarium cobalt holds its properties where NdFeB cannot survive: continuous service at 250–350°C, with far better temperature coefficients (Br ≈ −0.03 %/°C versus −0.12 %/°C). It also resists corrosion without coating. You pay 2–4× the price of NdFeB and accept lower strength and higher brittleness. For downhole tools, aerospace actuators and high-temperature motor duty, there is no substitute.
Ferrite — when cost rules
Ceramic ferrite delivers perhaps a tenth of NdFeB's energy product — at a fraction of the price, with intrinsic corrosion resistance and thermal stability to about 250°C. Where volume is available and cost dominates (appliance motors, speakers, magnetic separators, latching), ferrite remains unbeatable. It is also the reason "just switch to ferrite" rarely works: the size penalty is usually unacceptable in modern compact designs.
AlNiCo — when extreme temperature and stability rule
AlNiCo survives 450–550°C and has excellent thermal stability — but very low coercivity, meaning it demagnetizes easily from external fields or improper geometry. It lives on in precision instruments, watt-hour meters, sensors and high-temperature holding applications where its stability justifies careful design around its weakness.
The Decision Order That Prevents Mistakes
- Temperature first. Above ~200°C continuous, NdFeB exits and the choice narrows to SmCo, ferrite or AlNiCo. Above ~350°C, only AlNiCo remains.
- Then flux. Can the available volume deliver the required flux with the candidate material? If only NdFeB fits, the conversation becomes about grade and cooling.
- Then environment. Corrosive media, vacuum, radiation and sterilization cycles each eliminate candidates regardless of the numbers above.
- Cost last. Material cost optimized before the first three constraints are fixed is the most reliable way to buy the wrong magnet twice.
Not sure which window your application sits in? Send us your operating temperature, environment and flux target — material selection is the first thing we review on every inquiry, and we respond within 24 hours.