What do NdFeB magnet grade names like N42 or N50H mean?

NdFeB grade names follow the pattern: N + number + optional suffix. The 'N' denotes Neodymium-Iron-Boron. The number indicates maximum energy product (BH)max in MGOe — N42 has (BH)max ≈ 42 MGOe, N52 ≈ 52 MGOe. Higher numbers mean stronger magnets with higher remanence Br. The suffix (M, H, SH, UH, EH) indicates maximum operating temperature — blank/N = 80°C, H = 120°C, SH = 150°C, UH = 180°C, EH = 200°C.

What is the difference between Br, Hcb, and Hcj in permanent magnets?

Br (remanence) is the flux density at zero applied field — higher Br means a stronger magnet and more torque in a motor. Hcb (coercivity) is the field at which B = 0. Hcj (intrinsic coercivity) is the field at which the magnet permanently loses its magnetisation — higher Hcj means better resistance to demagnetisation from high currents or elevated temperatures.

How do I choose the right NdFeB magnet grade for my motor?

First, choose the grade number (N35–N52) based on required flux density and torque — higher numbers give more torque in a smaller package. Then choose the temperature suffix based on your maximum operating temperature: use H suffix for motors reaching 100–120°C, SH for 120–150°C, UH for 150–180°C. Always verify that Hcj at operating temperature exceeds the peak demagnetising field from the winding.

Material Selection

NdFeB magnet grades explained — remanence, coercivity, and energy product

Neodymium-iron-boron magnets are the dominant choice for high-performance permanent magnet motors. Understanding the grade naming system lets you read a datasheet, compare materials, and make confident selection decisions.

The three key properties

Remanence (B_r): The flux density a magnet retains after the magnetising field is removed. Measured in Tesla. A higher B_r means more flux per unit volume of magnet — allowing a smaller, lighter magnet for the same air-gap flux density.

Coercivity (H_cj): The intensity of the magnetic field required to reduce the magnet's magnetisation to zero. Measured in kA/m. A higher coercivity means the magnet is more resistant to demagnetisation — critical in motors where the stator field can act against the rotor magnets during fault conditions or overload.

Maximum energy product ((BH)_max): The maximum amount of magnetic energy stored per unit volume of the magnet, measured in kJ/m³ (or MGOe in older datasheets). This is the figure of merit for how efficiently the magnet material stores magnetic energy. The grade number in the NdFeB naming convention refers directly to this value.

N42 → (BH)_max ≈ 42 MGOe ≈ 334 kJ/m³ The number after N is the nominal maximum energy product in MGOe.

Demagnetisation B-H curve for NdFeB grades — Demagnetisation curve for N42 — showing remanence (B_r), coercivity (H_cj), and the operating line. Explore grades in the Permanent Magnets tool.

Reading the grade name

An NdFeB grade like N42SH contains two pieces of information: the number (42) gives the energy product, and the suffix (SH) gives the temperature class — that is, the maximum operating temperature up to which the coercivity remains adequate.

Suffix	Max operating temp.	Coercivity level
(none)	80 °C	Standard
M	100 °C	Medium
H	120 °C	High
SH	150 °C	Super High
UH	180 °C	Ultra High
EH	200 °C	Extremely High
AH	220 °C	Abnormally High

Note that higher temperature class grades achieve their improved coercivity by substituting some of the neodymium with dysprosium or terbium. This increases H_cj but slightly reduces B_r and significantly increases cost and supply chain risk, since dysprosium is a scarce heavy rare earth element.

NdFeB grade comparison table — Br, Hcj, BHmax — Quick reference table comparing NdFeB grades by B_r, H_cj, and (BH)_max — view the full table in the Permanent Magnets tool.

The energy product vs coercivity trade-off

You cannot maximise both B_r and H_cj simultaneously in a given alloy system. An N52 magnet has the highest energy product available commercially (~400 kJ/m³) but relatively low coercivity — making it suitable for room-temperature applications with no risk of demagnetisation. An N38EH magnet has lower energy product but survives continuous operation at 200 °C without irreversible demagnetisation.

For traction motors and servo drives, the operating temperature of the rotor magnets at maximum load — not just ambient temperature — determines the minimum required coercivity. Magnet temperature in a high-speed PMSM rotor can easily reach 120–160 °C under continuous rated load.

Selecting the right grade

Start with the operating temperature constraint: estimate magnet temperature at worst-case load and add a safety margin of 20–30 °C. This defines the minimum temperature class. Then, within that class, select the highest energy product grade your budget allows — it will give the most compact magnet for a given air-gap flux density.

For most EV and servo drive applications, N38SH or N40SH strikes a good balance — adequate temperature rating, high energy product, and reasonable availability. N52 is best reserved for applications where size and weight are critical and operating temperatures are well controlled.

Compare NdFeB grades and view demagnetisation curves

Browse B_r, H_cj, and (BH)_max data across grades and convert between SI and CGS units.

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