tools — thermal design

Magnet Temperature Derating Calculator

Every permanent magnet gets weaker as it heats up — and standard-grade neodymium loses strength faster than most engineers expect. Pick a material and grade below, set your operating temperature, and see the estimated reversible flux loss, remaining Br, and whether you're inside the material's safe operating window.

interactive — derating estimate

Reversible loss recovers when the magnet cools. Operation above the maximum operating temperature — or at a low permeance coefficient — adds irreversible loss on top of what's shown here (see below).

material family

ndfeb grade (typical Br)

operating temperature

80 °C · 176 °F

custom Br override — optional, in tesla

br at 20 °C — baseline—

reversible flux change—

estimated br at temperature—

max operating temperature—

remaining flux vs. 20 °C100%

within normal operating range

method — Br(T) = Br₂₀ × [1 + α(Br)·(T − 20)/100], using typical reversible coefficients for each family. Real coefficients vary by manufacturer and lot; for production designs, request the actual demagnetization curves for your material — our engineering team can supply BH curves at temperature for stocked grades.

reference — temperature coefficients by material

α(Br) is the reversible temperature coefficient of residual induction; β(Hcj) is the coefficient of intrinsic coercivity. Note that ferrite's β is positive — its coercivity improves when hot but collapses in the cold.

material	α(Br) %/°C typ.	β(Hcj) %/°C typ.	max op. temp*	curie temp
NdFeB — N (standard)	−0.12	−0.65	80 °C	≈ 310 °C
NdFeB — M	−0.12	−0.62	100 °C	≈ 320 °C
NdFeB — H	−0.12	−0.60	120 °C	≈ 320 °C
NdFeB — SH	−0.11	−0.55	150 °C	≈ 330 °C
NdFeB — UH	−0.11	−0.52	180 °C	≈ 340 °C
NdFeB — EH	−0.10	−0.50	200 °C	≈ 340 °C
NdFeB — AH	−0.10	−0.48	220 °C	≈ 350 °C
ceramic / ferrite (C8)	−0.20	+0.27	250 °C	≈ 450 °C
SmCo — 2:17 series	−0.035	−0.20	300 °C	≈ 800 °C
SmCo — 1:5 series	−0.045	−0.25	250 °C	≈ 750 °C
alnico 5	−0.02	—	525 °C	≈ 860 °C

* max operating temperature is geometry-dependent. Published limits assume a permeance coefficient around 1 or higher. A thin disc operating at PC ≈ 0.3 can suffer irreversible loss well below its rated maximum — this is the single most common thermal design mistake we see. Values above are typical of commercial material and vary by manufacturer.

beyond reversible — irreversible & structural loss

reversible loss	What this calculator shows. Flux drops with temperature along the coefficient and fully recovers on cooling. No damage done.
irreversible loss	Occurs when the working point drops below the knee of the intrinsic curve — from exceeding max operating temperature, from low permeance coefficient (thin magnets, large air gaps), or from opposing fields. Flux does not recover on cooling, but the magnet can be re-magnetized to full strength.
structural loss	Metallurgical change from approaching the Curie temperature, oxidation, or corrosion. Permanent — re-magnetization does not recover it.
cold-side risk (ferrite)	Because ferrite's Hcj falls as temperature drops, ceramic magnets in low-PC circuits can partially demagnetize below about −20 °C — the opposite failure mode from NdFeB. Check the cold end of your spec, not just the hot end.

practical guidance — choosing a grade for temperature

Rules of thumb our engineering team applies daily:

under 80 °C	Standard N grades (N35–N52). Buy energy product, not temperature rating you won't use.
80–150 °C	Move to H or SH suffixes. A common swap: N42 → N42SH holds nearly the same room-temperature Br but roughly triples the usable temperature margin on Hcj.
150–200 °C	UH/EH NdFeB — or evaluate SmCo 2:17, which often wins on total flux above ≈ 180 °C because its α is three times gentler.
above 200 °C sustained	SmCo or alnico territory. Alnico holds flux best of all but demagnetizes easily; keep it in a closed or high-PC circuit.
high-temp + thin geometry	Raise the grade suffix one step beyond what the temperature alone suggests. Thin discs and large gaps pull the working point toward the knee.

need the full grade picture? Our neodymium grades & tolerances reference covers Br/Hcj ranges for every stocked grade, and the pull force calculator shows what a derated Br does to holding force.

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