Sourcing Rare-Earth Magnets: Grade, Temperature Class, and the Heavy-Rare-Earth Chokepoint

NdFeB and SmCo magnets are specified on three axes buyers routinely collapse into one line item, grade, temperature class, and provenance. The heavy rare earths Dy and Tb that set the temperature class are also the part of the supply chain most concentrated in China. Specifying them precisely is the first move; second-sourcing them is the harder one.

A permanent magnet looks like a commodity and prices like one, which is why buyers tend to quote it as a single line: "N52, this many millimetres, this many pieces." That collapses three independent axes into one, and each of the three is where a sourcing decision actually lives. A rare-earth magnet is defined by its material family, its grade, its temperature class, and its provenance, and on the MPBxChange spec sheet for the vertical, those are distinct fields a supplier has to fill in, not a single keyword to match on.

The family comes first: Nd-Fe-B (neodymium-iron-boron), Sm-Co (samarium-cobalt), ferrite, or alnico. NdFeB delivers the highest energy product and dominates the high-performance end; SmCo trades some of that energy density for far better high-temperature and corrosion behaviour. Within a family, the magnet is then pinned down by grade, by temperature class, by its maximum energy product (BH)max, by coating, by geometry, and by whether it is sintered or bonded. Get the family and the grade right and miss the temperature class, and the part can still demagnetise in service.

The grade ladder and the temperature class are two different specs

Grade is the energy-density ladder, N42, N52, N55 and the rungs between. A higher number means a higher (BH)max, which for a motor designer means more torque from the same magnet volume. Buyers fixate on this number because it is the one that reads like "better." But grade says nothing about how hot the magnet can run before it starts to lose its field, and that is a separate axis entirely.

Temperature class is the second axis: N, M, H, SH, UH, EH. It is the maximum operating temperature ladder, and, critically, it is defined by the heavy-rare-earth content, dysprosium (Dy) and terbium (Tb), alloyed into the magnet. Adding Dy or Tb raises the coercivity that lets the magnet hold its field at temperature, which is how you climb from an N-class part to an SH, UH, or EH part. So the same N-grade energy density can be specified across a wide band of temperature classes, and the higher classes cost more not because they store more energy but because they carry more heavy rare earth. A traction motor, a downhole tool, or anything running hot needs the temperature class locked independently of the grade.

Why heavy rare earths are the bottleneck, not the magnet

The buyer-side note on the spec card is blunt: lock grade plus temperature class plus provenance, because the heavy rare earths Dy and Tb are the real bottleneck. That is a supply-chain statement, not a metallurgy one. Magnets themselves are made in many places. The rare-earth processing that produces the Dy and Tb feedstock, the exact elements the higher temperature classes depend on, is heavily concentrated in China. MPBxChange's corridor analysis carries the same structural pattern for adjacent verticals: roughly 80% of global solar module capacity and a majority of EV battery-cell output sit in China, and the corridor-concentration logic treats single-jurisdiction dependence as a category-level risk regardless of which supplier you pick.

“A buyer can second-source the magnet and still be single-sourced on the heavy rare earth inside it. The concentration lives one tier upstream, in the Dy and Tb that set the temperature class.”

· MPBxChange Research

That is the trap in a magnet RFQ. A buyer can second-source the magnet, qualify a maker in one jurisdiction, a backup in another, and still be single-sourced on the heavy rare earth inside both of them. The concentration does not live at the part level where the buyer is shopping; it lives one tier upstream, in the Dy and Tb that set the temperature class. Which is exactly why the spec-card guidance pairs temperature class with provenance: the moment a design needs an SH, UH, or EH part, it has taken on heavy-rare-earth exposure that a China-free or recycled-content provenance field is the only honest way to surface. Demand for high-temperature NdFeB is pulled by exactly the applications that run hot and cannot tolerate field loss, EV traction motors, wind-turbine generators, drones, and defense systems, which is what makes the heavy-rare-earth question strategic rather than academic.

What it means for procurement

• Quote grade, temperature class, and provenance as three separate fields, not one. (BH)max grade (N42 / N52 / N55) and temperature class (N / M / H / SH / UH / EH) are independent; a high grade with the wrong class still demagnetises in service.
• Treat the temperature class as a heavy-rare-earth flag, climbing from N-class to SH / UH / EH means more Dy and Tb, the part of the chain most concentrated in China.
• Recognise that second-sourcing the magnet is not second-sourcing the Dy, concentration sits one tier upstream of where you are shopping.
• Make provenance a hard field, China-free, recycled-content, or traceable, and ask suppliers to prove Dy-reduction or recycled-content capability rather than asserting it.
• Hold suppliers to the measurement and compliance standards, IEC 60404, ASTM A977, MMPA 0100, RoHS, REACH, so the grade and class on the quote are verifiable, not nominal.
• For EV-motor, wind, drone, and defense programs, add an alternate-jurisdiction source clause; the SE-Asia corridor (TH / VN / MY) is the platform’s named China-plus-one diversification anchor.