NdFeB Magnet Grades Explained - N35 to N55 and What the Letters Mean

The grade name has two parts: a number and an optional letter suffix. The number (35, 42, 52, etc.) is the Maximum Energy Product (BHmax) in MGOe (Mega Gauss Oersteds). An N42 magnet delivers up to 42 MGOe of magnetic energy per unit volume. Higher numbers mean more magnetic energy in the same physical size, which usually translates to stronger pull force in a smaller package. The letter suffix indicates the maximum operating temperature before the magnet begins to irreversibly demagnetize. No suffix (just 'N') means 80 degrees C. M means 100 degrees C. H means 120, SH means 150, UH means 180, EH means 200, and AH means 220+ degrees C. So an N48SH magnet delivers up to 48 MGOe and is stable to 150 degrees C.

• •N (no suffix): 80 degrees C max - consumer electronics, sensors, low-duty applications
• •M: 100 degrees C - small motors, audio equipment
• •H: 120 degrees C - industrial motors, pumps
• •SH: 150 degrees C - automotive, high-load motors, robotics
• •UH: 180 degrees C - EV traction motors, aerospace
• •EH: 200 degrees C - high-performance EV, defense
• •AH: 220+ degrees C - extreme thermal environments

Higher grade numbers and higher temperature ratings work against each other. An N55 magnet delivers the highest energy product available in commercial sintered NdFeB, but it is limited to 80 degrees C. If your motor runs at 150 degrees C, you are looking at N42SH or N38SH, which gives you less magnetic energy per unit volume but will not demagnetize in your operating environment. This is the core engineering decision: energy density versus thermal stability. Over-specifying the grade wastes money. Higher grades cost more due to tighter process controls and more selective raw material. Under-specifying risks irreversible demagnetization in the field, which means motor failure. There is no way to recover a demagnetized NdFeB magnet by simply re-magnetizing it if it has exceeded its thermal limit - the microstructure is permanently degraded.

The grade is not just a marketing label - it reflects the alloy composition and processing parameters. Higher energy products (higher numbers) require more precise control of the Nd2Fe14B grain structure during sintering: finer grain size, better alignment, and higher density. Higher temperature ratings (the letter suffixes) are achieved by adding heavy rare earth elements - primarily dysprosium (Dy) and terbium (Tb) - which increase the coercivity (Hcj) of the magnet. More Dy/Tb means higher temperature resistance but also higher cost, since these elements are expensive and subject to China's export controls. A standard N42 magnet might contain zero Dy. An N42SH might contain 2-4% Dy. An N38EH might contain 6-8% Dy. The raw material cost difference is substantial.

Grain Boundary Diffusion (GBD) technology is shifting the trade-off between performance and cost. Instead of mixing heavy rare earth elements throughout the entire magnet alloy, GBD applies a thin layer of Dy or Tb compound to the magnet surface and diffuses it inward through heat treatment. The heavy rare earths migrate along the grain boundaries - exactly where demagnetization initiates - while leaving the grain interiors as pure Nd2Fe14B. The result is the same high coercivity with 50-70% less heavy rare earth content. For engineers, this means you can now get SH or UH-level temperature performance at significantly lower cost and with less exposure to rare earth supply disruptions. GBD-processed magnets also preserve slightly higher remanence (Br) than conventionally produced magnets of the same temperature grade, because the grain interiors are not diluted by Dy/Tb.

Start with your worst-case operating temperature. This includes ambient temperature, self-heating from resistive losses in the motor windings, and eddy current heating in the magnet itself. Add a 20-30 degree C safety margin. That determines your suffix. Next, calculate the minimum BHmax your design requires. FEM (Finite Element Method) simulation is the most reliable way to do this - it accounts for the actual geometry, air gap, and operating point of your magnetic circuit. The intersection of your temperature requirement and your BHmax requirement is your grade. If N48SH meets both, do not specify N52SH just for margin - you are paying for energy product you do not need.

• •Step 1: Determine worst-case operating temp (ambient + self-heating + eddy current) and add 20-30 degree C margin
• •Step 2: Run FEM simulation to find minimum required BHmax for your geometry
• •Step 3: Select the grade at the intersection of those two requirements
• •Step 4: Ask your supplier about GBD options to reduce cost on SH/UH/EH grades

Different applications cluster around different grade ranges based on their thermal and performance profiles. Consumer electronics and sensors typically use N42 to N52 (standard N suffix) because operating temperatures are low and maximum flux density is desirable. Industrial motors and pumps commonly use N38H to N42H, balancing moderate temperature exposure with reasonable cost. Automotive and robotics applications concentrate on N45SH to N48SH, which provides strong flux density with reliability to 150 degrees C. EV traction motors push into N42UH to N45UH territory for continuous high-temperature duty. Aerospace and defense applications may require EH or AH grades for extreme thermal environments.

• •Consumer electronics / sensors: N42-N52 (80 degrees C)
• •Industrial motors / pumps: N38H-N42H (120 degrees C)
• •Automotive / robotics: N45SH-N48SH (150 degrees C)
• •EV traction motors: N42UH-N45UH (180 degrees C)
• •Aerospace / defense: N38EH-N42EH (200 degrees C)

When requesting quotes, do not just specify a grade name. Provide the minimum Br (remanence), minimum Hcj (intrinsic coercivity), and BHmax range you need. The grade name is a nominal designation - actual production values vary within a range. A good supplier will provide guaranteed minimums and share BH curve data from production batches, not just catalog values. Also ask whether GBD processing is available for your grade and geometry. For SH, UH, and EH grades, GBD can reduce your per-unit cost by 15-30% while matching or exceeding the magnetic performance of conventionally produced magnets.