Ferrite vs. NdFeB: Motor Selection Guide
When to pick hard ferrite over NdFeB in a motor: flux, volume and temperature trade-offs, and why the route is fixed before tooling.
Key Question & Key Takeaway
The question this guide answers, and the conclusion to start from.
When should an engineer specify Hard Ferrite over Neodymium Rare Earth magnets in motor design?
Ferrite needs no coating where the volume allows, with the grade's usable temperature confirmed per project. NdFeB is the route to evaluate where power density and a compact envelope leave ferrite no room.
Permanent magnet selection for electric motors is a balance between flux, available volume, operating temperature, corrosion exposure and the total manufacturing budget. The two materials that dominate industrial motor design are wet-pressed strontium hard ferrite and sintered NdFeB, and the decision between them is a balance of several requirements rather than a matter of preference.
The two families side by side
The listed property ranges for the two sintered families, taken from the grade tables on this site:
| Property | Sintered hard ferrite | Sintered NdFeB |
|---|---|---|
| Remanence (Br) | 380 – 460 mT (3800 – 4600 Gs) | 1020 – 1470 mT |
| Coercive force (HcB) | 160 – 354 kA/m (2010 – 4450 Oe) | 780 – 1035 kA/m as a grade floor (9.8 – 13.0 kOe) |
| Maximum energy product (BH)max | 27.0 – 41.8 kJ/m³ (3.4 – 5.3 MGOe) | 207 – 446 kJ/m³ (26 – 56 MGOe) |
| Maximum operating temperature | Confirmed per grade, process and project | 80 °C (N series) to 230 °C (AH series) |
| Magnetic orientation | Anisotropic or isotropic, depending on grade and process | Set during magnetic-field pressing |
| Corrosion and surface protection | Normally requires no coating | Commonly requires protection: Ni-Cu-Ni, zinc, epoxy, parylene or chemical passivation |
| What limits it in a motor | Energy density: volume for volume it delivers less flux than NdFeB | Corrosion: surface protection becomes a qualified process step, not a finish |
These are the listed ranges for the grades on this site, and bonded NdFeB sits below the sintered figures: compression molded 300 – 830 mT, injection molded 400 – 630 mT. The values are reference data; the grade supplied for a part is stated on its grade sheet and the order.
Which NdFeB series, and what the letter costs
An NdFeB grade name carries two facts: the number is the energy density, the letter is the coercivity series. The letter is the temperature decision, because the coercivity of the series is what sets the reverse field the magnet survives at temperature. The seven series published on this site run from N to AH:
| Series | HcJ floor | Max. operating temperature | Grades published |
|---|---|---|---|
| N | ≥955 kA/m (≥12 kOe) | 80 °C | N35 – N55 |
| M | ≥1114 kA/m (≥14 kOe) | 100 °C | 35M – 54M |
| H | ≥1353 kA/m (≥17 kOe) | 120 °C | 35H – 54H |
| SH | ≥1592 kA/m (≥20 kOe) | 150 °C | 35SH – 54SH |
| UH | ≥1990 kA/m (≥25 kOe) | 180 °C | 30UH – 52UH |
| EH | ≥2388 kA/m (≥30 kOe) | 200 °C | 28EH – 50EH |
| AH | ≥2786 kA/m (≥35 kOe) | 230 °C | 28AH – 45AH |
The coercivity is paid for at the top of the range, not in the middle. 35N and 35UH carry the same 263 – 287 kJ/m³ (33 – 36 MGOe), but the N series runs up to N55 at 422 – 446 kJ/m³ (53 – 56 MGOe) while the AH series stops at 45AH, at 342 – 366 kJ/m³ (43 – 46 MGOe). A part that has to hold its flux at 200 °C is therefore not simply a hotter version of the same magnet: it is a lower-energy grade at the top of its series, and the volume it loses has to be found in the circuit. The temperatures above are the series maximum published in the grade table; the grade supplied for a part is confirmed per project against the circuit, the load point and the reverse field it sees.
When ferrite is the right route
- There is enough volume in the magnetic circuit to reach the flux the motor needs.
- The working temperature is high enough that a coated NdFeB grade would become expensive or risky.
- The environment is corrosive enough that an unpainted, chemically inert ceramic oxide is an advantage rather than a limitation.
- Cost stability at volume matters more than minimum part size.
When NdFeB is the route to evaluate
- The design envelope is small and flux has to be maximized inside it.
- High (BH)max is required and no geometry can compensate for the available volume.
The trade-offs to state honestly
Ferrite's limit is energy density: volume for volume, NdFeB delivers higher flux, with the grades compared per project. Ferrite parts are also brittle, and arc segment stators require per-piece assembly and bonding, which adds tooling, labour and assembly-consistency requirements. NdFeB corrodes easily and must be supplied with surface protection, which becomes a qualified process step rather than a finish.
How this is decided in practice
Start from the volume the motor makes available, then from the temperature the magnet reaches under load rather than from ambient. Available volume is only one part of the selection. Compare the required flux, the full operating temperature range, reverse-field conditions, retention and corrosion exposure. Ferrite may need particular attention at cold start because coercivity decreases at lower temperatures. Validate a proposed substitution in the intended magnetic circuit. Substitution may require changes to magnet volume, magnetic circuit, orientation or assembly. If the existing envelope cannot meet the requirement in ferrite, retaining NdFeB may be the appropriate decision. The material route is settled at the first technical review, before tooling, because changing it later changes both the geometry and the assembly method.
Applies to permanent magnet selection for DC, BLDC and stepping motor designs where the magnet sits in a stator or rotor magnetic circuit. It covers the material decision itself; it does not cover grade-level selection within a material family, magnetization pattern, or the assembly and bonding method, which are confirmed per project.
Bring the decision to a technical review before tooling is ordered: the drawing or a sample, the space the motor leaves for the magnet, the highest and lowest temperature the part sees, the flux or force it has to meet, and the annual quantity. We say which of the two material routes the part can be assessed on, which points still need a measurement on your side, and what the choice would change in the geometry or the assembly. If the part already runs in one of the two materials and the objective is a second source or a substitution, say which platform and which part, so the review is scoped to that comparison.
Last reviewed: 26/10/2026
Material systems this note refers to.
- Hard Ferrite (Ceramic) Magnets Material System
Custom strontium ferrite magnets in wet-pressed, dry-pressed and injection-molded forms, tooled to your drawing or sample.
- Neodymium (NdFeB) Rare Earth Magnets Material System
Custom sintered, compression molded and injection molded NdFeB magnets for motors, sensors and industrial equipment.
Production routes this note refers to.
- Wet Pressed Ferrite Manufacturing Route
Ferrite slurry compacted in an orienting field and drained during pressing. The route for parts that need more flux per unit volume than dry pressing.
- Sintered NdFeB Manufacturing Route
NdFeB strip cast, milled, pressed in a field, sintered and heat treated. Rings, discs, blocks and arcs; the parts are brittle, so handling needs care.
Where this guidance is applied in service.
- Electric Motors & Drives Application
Stator arcs and rotor magnets for motors and drives. Wet-pressed ferrite is usual for stators, and cold start sets the demagnetization margin.
Discuss This Topic Against Your Own Drawing
Send the drawing, the sample parameters or the operating conditions, and we will review how this guidance applies to your project.