NdFeB Magnets Explained: Composition, Properties and Grades
NdFeB stands for neodymium, iron and boron: the three elements in the compound Nd₂Fe₁₄B that gives these magnets their strength. NdFeB magnets are the strongest permanent magnets in mass production. Developed in the early 1980s by Sumitomo Special Metals and General Motors, they made compact, efficient electric motors possible, and they are now the main reason investors care about rare earths.
NdFeB Magnet Composition
| Ingredient | Share | Role |
|---|---|---|
| Iron (Fe) | Most of the weight | Forms the magnetic backbone of the Nd₂Fe₁₄B crystal |
| Neodymium and praseodymium (Nd, Pr) | Roughly a third of the weight in typical grades | Provide the high magnetic strength |
| Boron (B) | About 1% | Stabilises the crystal structure |
| Dysprosium and terbium (Dy, Tb) | Small additions in high-temperature grades | Keep magnets from losing strength when hot |
NdFeB Magnet Properties
| Property | Typical value | What it means |
|---|---|---|
| Density | About 7.4 to 7.7 g/cm³ (typically 7.5) | Similar to steel; roughly 7.5 times the density of water |
| Maximum energy product (BH)max | Up to about 50 to 53 MGOe (about 400 to 420 kJ/m³) for N52 | The grade number is roughly the energy product in MGOe, so N42 is about 42 MGOe |
| Remanence (Br) | About 1.4 T for top grades (1.42 to 1.48 T for N52) | How strong the magnet is once magnetised |
| Coercivity (Hcj) | From about 11 kOe (plain N) to 35 kOe or more (AH classes) | Resistance to demagnetisation; raised by adding Dy or Tb |
| Curie temperature | About 310 to 400 °C, depending on composition | The point where the magnet stops being ferromagnetic; usable temperatures are far lower |
| Physical form | Hard and brittle; corrodes unless coated | Most magnets are coated, commonly with nickel |
Values are typical ranges from manufacturers' datasheets, such as Eclipse Magnetics and HGT Advanced Magnets. Individual products and suppliers vary.
Magnet Grades and Temperature
NdFeB grades are named by strength and temperature class. The number, such as N42 or N52, reflects the energy product, and the letters (none, M, H, SH, UH, EH, AH) reflect coercivity and therefore the maximum operating temperature. Higher temperature classes need more dysprosium or terbium and give up some strength, which is why the strongest grades, such as N52, exist only in the standard class.
| Grade class | Typical maximum operating temperature |
|---|---|
| N (standard) | About 80 °C |
| M | About 100 °C |
| H | About 120 °C |
| SH | About 150 °C |
| UH | About 180 °C |
| EH | About 200 °C |
| AH | About 220 to 230 °C |
Ratings vary by supplier. The maximum operating temperature is not the Curie temperature: magnets start to lose strength irreversibly well below the Curie point.
Dy/Tb Grain Boundary Diffusion: Using Less Heavy Rare Earth
Dysprosium and terbium raise coercivity, but mixing them through the whole alloy is costly and lowers remanence and energy product. Grain boundary diffusion avoids that. A compound containing dysprosium or terbium is applied to the surface of a finished magnet, which is then heat treated so the heavy rare earth moves in along the grain boundaries and forms a shell around each grain. The shell raises coercivity where it is needed while the grain cores keep their strength.
- Advantages of Dy/Tb diffusion magnets: less heavy rare earth per magnet, lower cost, and a smaller loss of remanence than conventional alloying.
- Limits: diffusion only penetrates part of the way into a magnet, so it works best for thinner sections.
For the research, see this peer-reviewed study of terbium grain boundary diffusion. Diffusion is one reason magnet makers can cut heavy rare earth use per magnet even as EV demand grows.
Sintered, Bonded and Hot-Deformed Magnets
- Sintered magnets are made by pressing alloy powder in a magnetic field and heating it until it fuses. They are the strongest and are used in EV motors and wind turbines.
- Bonded magnets mix magnetic powder with a polymer and are moulded into complex shapes. They are weaker but suit small motors and sensors.
- Hot-deformed (die-upset) magnets start from melt-spun powder that is hot pressed and then deformed. This aligns the grains without an orienting magnetic field, which suits radially oriented ring magnets, but the process route is more expensive.
NdFeB Magnet Applications
- Electric vehicles: traction motors in most EVs.
- Wind turbines: permanent magnet generators, especially direct-drive designs.
- Industrial motors and robotics: efficient, compact servo and drive motors.
- Electronics: hard drives, speakers, headphones and phone vibration motors.
- Defense and aerospace: actuators and guidance systems, often with high-temperature grades.
Alternatives to Rare Earth Magnets
| Alternative | Trade-off |
|---|---|
| Ferrite magnets | Cheap and rare-earth free, but much weaker, so motors must be larger |
| Samarium-cobalt magnets | Excellent at high temperature but costlier and less powerful at room temperature |
| Induction motors | No permanent magnets; used by some EV makers, typically less efficient at part load |
| Externally excited synchronous motors | Use electromagnets instead of permanent magnets; used by some carmakers, including BMW |
Higher rare earth prices or supply shortages push more manufacturers towards these alternatives, which is one of the main long-term risks to rare earth demand. The rare-earth-free magnets section below shows how far each route has got.
Rare-Earth-Free Magnets and Motors: How Far Along Are They?
Rare-earth-free motors are already in production at some carmakers, but they have not displaced NdFeB magnets, and the best-known rare-earth-free magnet, iron nitride, is not yet in commercial volume. Most routes trade size, efficiency or cost for freedom from rare earths.
| Route | Status | Trade-off or open question |
|---|---|---|
| Electrically excited synchronous motors (EESM) | In production: BMW (fifth-generation eDrive, including the Neue Klasse iX3) and Renault (5, Megane and Scenic E-Tech) | Typically less efficient on the WLTP test cycle and costlier to build than permanent magnet motors |
| Ferrite magnet motors | Established technology | Ferrite magnets are much weaker than neodymium, so motors must be larger for the same power |
| Iron nitride magnets (Niron Magnetics) | Pilot plant in Minneapolis since 2024; a 1,500 tonne a year plant in Sartell, Minnesota is under construction, with production expected in 2027 | Performance claims come mainly from the company; independent data sheets are awaited, and skeptics point to low resistance to demagnetisation |
| Tesla rare-earth-free motor | Tesla said in September 2026 that its Cybercab motor contains no rare earth metals | The magnet type is not confirmed, and Electrek argues the impact is smaller than it sounds |
Sources: Niron Magnetics; Enterprise Minnesota; IDTechEx; Interesting Engineering; Electrek.
- Iron nitride financing: in August 2026 Niron announced a $150 million loan from the Shakopee Mdewakanton Sioux Community, and it holds a conditional commitment of up to $150 million from the US Department of War's Office of Strategic Capital.
- What is unproven: Niron says its magnets exceed most NdFeB grades in magnetic strength and temperature stability, but those claims come from the company and conference abstracts. Critics note that iron nitride's coercivity is much lower than NdFeB's, which limits its use in hot, high-demand traction motors.
- Forecast, not fact: S&P Global Mobility is reported to expect rare-earth-free motor demand to grow about 15% a year over the next decade, with their share roughly tripling by 2037. Rare earth use in motors remains high today.
- For investors: substitution is a gradual risk to long-term NdPr demand, not a near-term one. Watch carmaker motor choices, Niron's 2027 output and published data sheets, and the rare earth price level, since higher prices speed substitution.
Who Makes the Magnets
China makes most NdFeB magnets. Who makes them, and where new plants are being built outside China, is covered in the rare earth magnet value chain, and listed makers are compared on the publicly traded magnet makers page.
NdFeB Magnets FAQ
What does NdFeB stand for?
NdFeB stands for neodymium, iron and boron, the three elements that make up the magnetic compound Nd₂Fe₁₄B. The name is also written Nd-Fe-B, and the magnets are often called neodymium magnets.
What is an NdFeB magnet?
An NdFeB magnet is a permanent magnet made mainly of neodymium, iron and boron. NdFeB magnets are the strongest permanent magnets in mass production and are used in EV motors, wind turbines, electronics and industrial machinery.
What is the density of NdFeB magnets?
The density of sintered NdFeB magnets is about 7.4 to 7.7 grams per cubic centimetre, typically around 7.5. That is similar to steel, so NdFeB magnets are heavy for their size.
What is the Curie temperature of NdFeB?
The Curie temperature of NdFeB is roughly 310 to 400 degrees Celsius, depending on composition. Magnets lose strength at much lower temperatures than this, so their maximum operating temperature, from about 80 °C for standard grades to about 200 °C for the highest classes, matters more in practice.
Who invented NdFeB magnets?
NdFeB magnets were developed independently in the early 1980s by Sumitomo Special Metals in Japan and General Motors in the United States.
Why do NdFeB magnets need dysprosium and terbium?
NdFeB magnets lose strength as they heat up. Adding small amounts of dysprosium or terbium raises their coercivity, which keeps them working at the high temperatures found in EV motors. Magnet makers increasingly apply these heavy rare earths only at the grain boundaries to use less of them.
Can EV motors work without rare earth magnets?
Yes, some EV motors work without rare earth magnets. BMW and Renault build electrically excited synchronous motors, and induction motors are also used. Most EV makers still use NdFeB magnets because they give compact, efficient motors, and rare earth free motors are a small but growing share.
What is an iron nitride magnet?
An iron nitride magnet is a rare-earth-free permanent magnet based on an iron and nitrogen compound (alpha double prime Fe16N2). Niron Magnetics is building the first commercial plant, a 1,500 tonne a year facility in Sartell, Minnesota, with production expected in 2027. Its performance claims have not yet been independently verified in published data sheets.