- BHmax (Maximum Energy Product)
- The peak product of B and H on the second-quadrant demagnetization curve. Measured in MGOe (US/imperial) or kJ/m³ (SI). 1 MGOe ≈ 7.96 kJ/m³, so an N52 grade at ~52 MGOe is ~414 kJ/m³. BHmax is the closest single number to 'magnet strength', but it is measured at the operating point that maximizes energy density, which is not necessarily where your magnet runs in service.
- Br (Remanence)
- The magnetic flux density a magnet retains after the magnetizing field is removed and the external return path is closed. For NdFeB, Br ranges roughly 1.20-1.48 T (12.0-14.8 kGs) across N35 to N52. Higher Br means more flux at the magnet face for a given geometry. Br is a material property of the saturated grade and does not depend on shape.
- Coercivity (HcJ vs HcB)
- Two different coercivity values, both reported on every NdFeB spec sheet. HcB is the field at which B = 0 in the bulk; HcJ is the intrinsic coercivity, the field at which the material itself fully demagnetizes. HcJ is the design-relevant number for predicting irreversible loss, especially at temperature. Engineers asking only for 'coercivity' often get the wrong number; specify HcJ for thermal margin and HcB for circuit calculations.
- Curie Temperature vs Operating Temperature
- Two temperatures that are routinely confused. Curie temperature (Tc) is where ferromagnetic ordering vanishes entirely (~310-340°C for NdFeB). Maximum operating temperature (Tmax) is the much lower limit at which a specific grade begins to lose magnetization irreversibly (80°C for N52, up to ~200°C for EH grades). Designs must respect Tmax, not Tc. A magnet operating at 150°C is well below Tc but above the rating of all standard-series grades.
- Demagnetization Curve
- The second-quadrant of the B-H hysteresis loop, the part shown on every NdFeB datasheet. The y-intercept is Br, the x-intercept is HcB, and the curve's shape between them tells you how much demagnetizing field the magnet can tolerate before irreversible loss. A 'square' loop holds flux until close to HcJ; a sloped loop bleeds flux earlier. Always read the curve at your operating temperature, not at 20°C, when designing.
- GBD (Grain Boundary Diffusion)
- A process for adding heavy rare earths (Dy, Tb) to the grain boundaries of a sintered NdFeB magnet rather than alloying them throughout the bulk. Diffuses the heavy element via vapor or paste at elevated temperature. Result: equivalent or better high-temperature performance with 30-60% less Dy/Tb than a conventionally alloyed grade. GBD is how SH/UH/EH grades stay economically viable as heavy-rare-earth pricing fluctuates.
- Grade Suffixes (M, H, SH, UH, EH)
- The letters after the N-number indicate the grade's high-temperature class, achieved by heavy-rare-earth content. No suffix = 80°C, M = 100°C, H = 120°C, SH = 150°C, UH = 180°C, EH = 200°C. Higher classes need more Dy and/or Tb, raise cost, and trigger MOFCOM export licensing for shipments out of China at SH and above. Pick the lowest class that survives your worst-case operating temperature with margin.
- Magnetization Direction
- How the magnetic poles are oriented relative to the magnet's geometry. Axial: poles on the flat faces of a disc or block. Radial: poles on the curved inner and outer surfaces of a ring. Diametric: poles across the diameter of a disc or rod. Multipole: alternating poles around a ring (e.g. 8-pole, 12-pole) used in motor rotors. Magnetization direction is a sintering and magnetizing-fixture decision, not something the buyer changes after the fact.
- MOFCOM Export Licensing
- China's Ministry of Commerce export-control regime that, since April 2025, requires per-shipment licensing for SH, UH, and EH grade NdFeB magnets and certain heavy rare earth oxides. Approval is routine for documented commercial end-uses (EVs, robotics, industrial motors); rejections concentrate on defense-adjacent or unclear-end-use applications. Practical impact: budget 45-60 days for license review on top of production lead time, and source from factories that hold their own licensing rather than trading companies that route through third parties.
- NiCuNi Coating
- Triple-layer electroplated coating: nickel strike, copper interlayer, nickel topcoat. Standard finish on most sintered NdFeB. The copper layer provides ductility and improves corrosion resistance; the outer nickel gives wear and chemical resistance. Total thickness typically 15-25 µm. NiCuNi is not the same as 'nickel coating' (single Ni layer) which has noticeably worse salt-spray performance. Specify NiCuNi when corrosion matters; specify single-Ni only for cost-sensitive interior parts.
- PPAP (Production Part Approval Process)
- AIAG-defined automotive supplier qualification protocol. PPAP packages document that a part meets design intent and the supplier can produce it consistently, across 18 elements: design records, FMEA, control plan, capability studies, dimensional results, material certifications, etc. Levels 1-5 specify how much of the package is shipped vs retained. For NdFeB magnets going into IATF 16949 programs, PPAP at Level 3 is the typical entry bar; expect 8-16 weeks for a first PPAP and 2-4 weeks for engineering changes after that.
- Sintered vs Bonded NdFeB
- Two different process families. Sintered NdFeB is full-density (7.4-7.6 g/cm³), produced by pressing and high-temperature sintering of fine powder, then ground to final dimensions. BHmax 30-53 MGOe, mechanically brittle, requires coating. Bonded NdFeB embeds the same powder in a polymer matrix (epoxy, nylon), molded or extruded to near-net shape. BHmax 5-15 MGOe, mechanically tough, complex geometries possible. Sintered for performance; bonded for shape complexity at moderate flux.
- Temperature Coefficient (α, β)
- Two numbers that predict how Br and HcJ change with temperature. α is the reversible temperature coefficient of Br (~-0.12%/°C for NdFeB, meaning 1.2% Br loss per 10°C rise). β is the temperature coefficient of HcJ (~-0.6%/°C, the larger and more design-critical number). Both are reversible up to a point. Past Tmax, loss becomes partially irreversible; past the knee of the demag curve at temperature, it becomes catastrophic. Always model worst-case temperature using these coefficients, not nominal-temperature specs.
- Working Point
- Where a magnet sits on its demag curve once installed in its actual magnetic circuit. Determined by the geometry of the magnet, the air gap, and the iron return path. A magnet operates between Br (closed circuit, no gap) and HcB (short circuit, infinite gap); the load line from the origin intersects the demag curve at the working point. Designs are usually optimized for working point near BHmax. If the working point sits below the knee of the demag curve at operating temperature, expect irreversible loss.
Related:Sintered vs Bonded NdFeB
Related:Sintered vs Bonded NdFeB
Related:MOFCOM Export Licensing
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