Every magnet data sheet leads with the same four numbers: Br, Hcb, Hcj and (BH)max. Learn them and you can compare magnets with confidence.
Br — the strength that stays
Remanence (Br) is the magnetic strength a magnet keeps after it has been magnetized and the magnetizing field is switched off — the material's strength ceiling. In NdFeB it runs from about 1.08 T (low grades) to 1.45 T (N52).
Hcb — how hard to weaken
Coercivity (Hcb) is the opposing field needed to cancel the magnet's output. The higher it is, the harder the magnet is to weaken — by another magnet, coil, or steel part.
Hcj — how hard to kill
Intrinsic coercivity (Hcj) is the opposing field needed to destroy the magnet's internal magnetization for good — cross this line and the magnet is permanently weakened. Hcj also decides heat resistance; that is what the letters in N35H or N42SH mean.
(BH)max — the total energy
Maximum energy product ((BH)max) is the magnetic energy a magnet stores per unit of volume — the most quoted strength figure. The number in a grade name, like 42 in N42, is the energy product in MGOe. Higher means a smaller magnet can do the same job.
At a glance
| Symbol | Name | Meaning | NdFeB range |
|---|---|---|---|
| Br | Remanence | Strength left after magnetizing | 1.08–1.45 T |
| Hcb | Coercivity | Field that cancels the output | 700–1000 kA/m |
| Hcj | Intrinsic coercivity | Field that destroys it for good | 800–2400+ kA/m |
| (BH)max | Max. energy product | Magnetic energy per volume | 25–55 MGOe |
Typical commercial ranges at room temperature.
Which one matters most?
Br and (BH)max answer "how strong?", Hcj answers "how tough?" — and toughness often matters more. A motor magnet does not need the highest (BH)max; it needs an Hcj that survives heat and opposing fields without permanent loss. Grades explained shows how the letters combine.
Read on: the hysteresis loop → · materials compared →