NdFeB Temperature Classes Explained: What N, M, H, SH, UH, EH and AH Actually Mean

Every sintered neodymium grade has two parts: a number and, usually, a letter. N42, N42M, N42H, N42SH, N42UH, N42EH. The number gets all the attention. The letter is what decides whether the magnet is still a magnet after a summer in an engine bay.

This guide explains how the temperature classes are defined, what physically changes in the material from one class to the next, why “maximum operating temperature” is a rule of thumb rather than a specification, and how to choose a class from your actual application instead of from a table.

The Letter Is a Coercivity Class, Not a Temperature Rating

The suffix on an NdFeB grade does not directly encode a temperature. It encodes a minimum intrinsic coercivity (Hcj) — the reverse magnetic field required to demagnetize the material. Temperature resistance follows from coercivity, because heat lowers Hcj and a magnet that starts with more coercivity has more to lose before it fails.

The industry-standard classes and their minimum Hcj values:

Class	Min. Hcj (kOe)	Min. Hcj (kA/m)	Nominal max operating temp*	Common name
N (no letter)	≥ 12	≥ 955	80 °C / 176 °F	Standard
M	≥ 14	≥ 1,114	100 °C / 212 °F	Medium
H	≥ 17	≥ 1,353	120 °C / 248 °F	High
SH	≥ 20	≥ 1,592	150 °C / 302 °F	Super High
UH	≥ 25	≥ 1,990	180 °C / 356 °F	Ultra High
EH	≥ 30	≥ 2,388	200 °C / 392 °F	Extra High
AH (TH)	≥ 33–35	≥ 2,626–2,786	220–230 °C / 428–446 °F	Top grade

*Nominal maximum operating temperature assumes a magnet with a permeance coefficient of roughly 1 or higher and no significant opposing field. See “Why the Table Temperature Is Only a Starting Point” below.

A few things worth noticing in that table. Each step up roughly adds 3–5 kOe of coercivity and 20–30 °C of nominal temperature capability. The nominal temperatures are conventions the industry has settled on, not test results tied to your part. And the “N” class isn’t rated to 80 °C because something magical happens at 81 °C — it’s rated there because a typical magnet shape with Hcj of 12 kOe starts to lose flux irreversibly somewhere in that neighborhood.

What Changes in the Material

All NdFeB temperature classes are the same base alloy — Nd₂Fe₁₄B — with different amounts of heavy rare-earth elements substituted for some of the neodymium. Dysprosium (Dy) and, to a lesser extent, terbium (Tb) raise the material’s anisotropy field, which raises Hcj.

The trade-offs are direct:

Coercivity goes up. That’s the whole point. More Dy means a higher Hcj and a higher usable temperature.
Remanence goes down. Dy substitution reduces Br. This is why the highest available grade number falls as the class rises: you can buy N52, but the top of the EH range is around N38EH and the top of AH is around N33AH. An N52 magnet doesn’t exist in SH.
Cost goes up. Dysprosium is far scarcer and more price-volatile than neodymium. An SH or UH magnet can cost meaningfully more than a plain N grade of the same size — often 30–100% more depending on the market — and EH/AH more still.
The temperature coefficient of Hcj improves. Higher-class grades typically have a β(Hcj) toward −0.50 %/°C, versus −0.60 to −0.70 %/°C for plain N. So high-coercivity grades not only start with more Hcj, they lose it a little more slowly per degree.

Newer manufacturing methods — grain-boundary diffusion in particular — put Dy only at the grain boundaries where it does the most good, reaching the same Hcj with less heavy rare earth. Practically, this means the Br penalty for a given class is smaller than it was ten years ago, and some suppliers now offer, for example, N45SH where N42SH was once the ceiling. Always check the supplier’s actual grade table rather than assuming a class’s upper limit.

Reversible vs. Irreversible Loss: Why Coercivity Matters

Every NdFeB magnet loses flux as it warms up, regardless of class. Br drops about 0.11–0.12% per °C for all grades. Take an N42 from 20 °C to 100 °C and it’s delivering roughly 9% less flux. That loss is reversible — cool the magnet and the flux comes back. It’s the same for N42 and N42EH, and no temperature class avoids it.

What the class controls is the irreversible loss. As the magnet heats, Hcj falls five to six times faster than Br. At some temperature the operating point of the magnet crosses the “knee” of the intrinsic demagnetization curve, and a portion of the magnetic domains flip. That flux does not come back on cooling. The magnet has been partially demagnetized and will read low on a Helmholtz coil or gaussmeter forever.

The temperature at which that happens depends on three things:

The starting Hcj — the temperature class.
The magnet’s operating point — set by its shape and magnetic circuit (the permeance coefficient).
Any opposing field — from a stator winding, a nearby magnet, or a magnetizing fixture in reverse.

The class only fixes the first. The table’s maximum operating temperature quietly assumes favorable values for the other two.

Why the Table Temperature Is Only a Starting Point

This is where most under-specification happens. A buyer sees “SH = 150 °C,” the application runs at 130 °C, and the part gets ordered — then the thin disc magnet in the assembly loses 15% of its flux in the first thermal cycle.

The published maximum temperature assumes a permeance coefficient (Pc) of about 1 — a magnet roughly as long in the magnetization direction as it is across. Real parts often aren’t:

Geometry (axially magnetized)	Approx. Pc	Practical effect
Disc, thickness = ¼ diameter	~0.3	Operates near the knee even at room temp; derate the class temperature by 30–50 °C
Disc, thickness = ½ diameter	~0.7	Somewhat below table assumption; derate 10–20 °C
Cylinder, length = diameter	~1.0–1.2	Table temperature applies
Rod, length = 2× diameter	~2.5+	Comfortable margin above table temperature
Any shape in a closed steel circuit	High	Table temperature applies or better

A flat N42 disc might survive only 60 °C before permanent loss. The same material as a long rod, or seated in a steel pot, might be fine at 90 °C. This is also why a magnet’s temperature rating is not really a property of the material — it’s a property of the material in a specific part in a specific assembly.

For radially magnetized rings the same logic applies with wall thickness in the magnetization direction. A thin-wall radial ring on a non-magnetic hub has a low Pc; the same ring pressed onto a steel back-iron has a much higher one. This is one of several reasons a true radial ring and a segmented arc assembly of the same grade don’t always behave the same way in the same motor.

Use the Magnet Demagnetization & Permeance Coefficient Calculator to check the actual Pc and operating-point margin of a proposed geometry at your temperature. It’s a far better screen than the table.

Opposing Fields Move the Limit Further

In a motor or actuator, the magnet doesn’t just have to survive heat — it has to survive heat while the stator is pushing back. Peak current, short-circuit faults and locked-rotor conditions all produce a demagnetizing field that shifts the operating point further toward the knee. A design that’s safe at 120 °C with the windings off can be marginal at 120 °C under fault current.

Motor designers routinely specify one class higher than the ambient temperature alone would suggest, for exactly this reason. Under-hood EV sensor and actuator magnets are commonly SH or UH even where the measured temperature never exceeds 120 °C.

Choosing a Class: A Practical Method

Establish the real maximum magnet temperature. Not ambient — the magnet. Include self-heating from adjacent windings, solar load, sterilization or reflow cycles, and worst-case transients. If the part sees 85 °C continuously with 110 °C excursions, design for 110 °C.
Estimate the permeance coefficient. From the magnet’s dimensions and whether it’s in a steel circuit. Below about 0.5, plan to go up a class regardless of what the table says.
Identify any opposing field. If there is one, quantify it in kOe or kA/m at worst case and go up another class if it’s significant.
Pick the lowest class that clears all three with margin. Then check that the Br you need is still available in that class. If you need N50 performance at 150 °C, you have a design problem, not a sourcing problem — no such grade exists, and the fix is more magnet volume or a better circuit.
Verify. For anything with a PPAP, validation, or field-failure consequence, run a thermal exposure test: measure flux (Helmholtz coil or fluxmeter), soak at the maximum design temperature plus margin, cool, re-measure. Irreversible loss should be under 1–2%. A published class is a starting point; the test is the specification.

Common Mistakes

Specifying “N42” for a 100 °C application. N42 without a suffix is an 80 °C grade. Above that, the suffix is part of the spec, and a drawing that reads “N42” leaves the supplier to guess.
Buying EH “to be safe.” If the part lives at 60 °C, EH costs more, delivers less flux and buys nothing. Match the class to the need.
Trusting the class on a thin magnet. A 10 × 1 mm disc in “SH” is not a 150 °C part. Check the Pc.
Ignoring assembly processes. Adhesive cure ovens, potting, overmolding and solder reflow can expose a magnet to temperatures the application never will. A 150 °C epoxy cure on an N grade magnet demagnetizes it before it ships.
Confusing max operating temperature with Curie temperature. The Curie point (roughly 310–340 °C) is where the material stops being ferromagnetic entirely. It’s irrelevant to selection; the magnet was ruined 150 °C earlier.
Assuming all suppliers’ classes are identical. The Hcj minimums are broadly standardized, but the temperature figures and the top available grade in each class vary by supplier. Request the datasheet, and for validated parts request lot test data. Our guide to reading a magnet datasheet covers what to look for.

Quick Reference by Application

Typical application	Typical magnet temp	Usual class
Consumer products, holding, closures, packaging	< 60 °C	N
Indoor sensors, encoders, reed switch actuation	60–90 °C	N or M
Industrial motors, pumps, couplings (not sealed)	90–120 °C	H
Automotive/EV sensors, under-hood actuators, servo motors	120–150 °C	SH
Traction motors, high-density BLDC, aerospace actuators	150–180 °C	UH
Downhole tools, steam-sterilized medical devices, high-temp brakes	180–200 °C+	EH / AH, or consider SmCo

Above about 200 °C, or where the flux density at temperature matters more than room-temperature strength, samarium cobalt (SmCo) often wins. Sm₂Co₁₇ grades run to 300–350 °C with a Br temperature coefficient of only about −0.03 %/°C — a quarter of NdFeB’s. At 180 °C, a mid-grade SmCo can out-deliver an N38EH. Our Magnets 201 guide compares the two materials in more depth.

Frequently Asked Questions

What does the SH in N42SH mean?

“SH” is the coercivity class, indicating a minimum intrinsic coercivity of 20 kOe (about 1,592 kA/m) and a nominal maximum operating temperature of 150 °C. The “42” is the maximum energy product in MGOe. N42SH has the same room-temperature strength as N42 but resists demagnetization at higher temperatures.

Is N52 available in a high-temperature grade?

No. Adding the dysprosium needed for higher coercivity lowers remanence, so the highest grade number available drops with each class. Typical ceilings are around N52 (N), N50M, N48H, N45SH, N42UH, N38EH and N33AH, though these shift as manufacturing improves. Confirm with the supplier’s grade table.

Does a higher temperature class mean a stronger magnet?

No. Within the same grade number, all classes have the same nominal Br and BHmax at room temperature. The higher class only holds that strength at higher temperatures and under stronger opposing fields. If anything, the top available strength is lower in higher classes.

Can I use an N-grade magnet above 80 °C?

Sometimes. A long magnet or one in a closed steel circuit has a high permeance coefficient and may tolerate 90–100 °C with minimal irreversible loss. A thin disc will not. Check the permeance coefficient and test the actual part rather than relying on the nominal figure.

Does the temperature rating change with magnet size?

Yes — through shape rather than absolute size. What matters is the ratio of length in the magnetization direction to cross-sectional dimensions (the permeance coefficient). Two magnets of the same class and grade but different aspect ratios can have usable temperature limits 50 °C apart.

What happens if a magnet exceeds its rated temperature?

It loses part of its magnetization permanently. The loss can be small (a few percent) or nearly total depending on how far past the knee the operating point went. Once demagnetized, the only fix is re-magnetization in a fixture, which is rarely practical for an assembled part.

Related Temperature & Grade Resources

Radial Magnets stocks over 10 million NdFeB magnets in the U.S. across standard and high-coercivity classes, including true radially magnetized rings for motor and sensor applications. Request a quote or contact us to discuss your operating temperature.