Dysprosium and terbium are added to NdFeB magnets to increase coercivity so that the magnets can operate at higher temperatures without losing their magnetic properties.
Dysprosium raises intrinsic coercivity and slows magnetic-property loss as temperature rises, making the requirement a function of service temperature and demagnetizing stress rather than a universal recipe [S1][S2].
4–5% Dy Is a Practical High-Temperature Reference
Dysprosium can be added to a conventionally produced NdFeB magnet to improve its resistance to demagnetization and high-temperature performance. Arnold Magnetic Technologies describes this range as necessary to resist demagnetization and support high-temperature performance [S1].
The quantity must be tied to a magnet grade and maximum operating temperature, not copied from a generic datasheet.
That distinction matters because adding more dysprosium is not automatically better. Dysprosium is used in NdFeB magnets to improve their resistance to demagnetization and, by extension, their high-temperature performance.
Dy Requirements Track Coercivity and Service Temperature
For applications above that range, dysprosium or terbium is used to preserve performance by replacing part of the neodymium in the sintered NdFeB phase [S2][S8].
No single Dy percentage guarantees acceptable service performance. The magnet must retain its required magnetic output under the combined temperature and demagnetizing conditions. This is why supplier grade selection and application testing are more defensible than treating 4–5 wt% as a universal formulation rule [S1][S2].
Compare Conventional Dy Alloying and Grain Boundary Diffusion
Dysprosium and terbium are used in NdFeB magnets to increase coercivity so that the magnets can operate at higher temperatures without losing their magnetic properties. This route is straightforward and established, but it increases exposure to Dy price and supply volatility [S2].
Grain boundary diffusion instead adds a secondary manufacturing step that concentrates dysprosium or terbium in the magnet's grain boundaries. The technique retains much of the high-temperature benefit while using less heavy rare earth metal [S2]. It is therefore a process and metallurgy decision, not simply a lower nominal Dy percentage written on a purchase order.
Heavy-rare-earth-free NdFeB is a third route.
Cerium-Cobalt Is a Research Route, Not a Drop-In Grade
Cerium-cobalt co-doping has demonstrated a path toward reducing or eliminating dysprosium in NdFeB. Ames Laboratory reported materials at least 20–40% cheaper than Dy-containing magnets, with intrinsic coercivity exceeding that of Dy-containing magnets at temperatures above 150 °C [S3].
The mechanism was to counter cerium's reduction of Curie temperature by co-doping with cobalt, allowing cerium to substitute for dysprosium without losing the required magnetic properties [S3]. One research statement summarized the result: “This material works better than anything out there at temperatures above 150°C” [S3].
That work does not establish that every high-temperature motor can use cerium-cobalt NdFeB. Commercial qualification, mechanical properties, long-term aging behavior, corrosion protection, machining, supply availability, and application-specific coercivity all remain separate engineering gates. For procurement, a qualified commercial grade or a validated diffusion process is safer than treating laboratory alloying as an immediate replacement.
High-Temperature NdFeB Is Not the Right Choice for Every Design
Dy-bearing NdFeB is appropriate for applications requiring high coercivity and resistance to demagnetization at elevated temperature, especially electric motors and generators [S2]. It is not necessary for low-temperature or lightly loaded static applications where ordinary NdFeB provides sufficient coercivity and a lower material penalty is desirable [S1][S7].
Samarium-cobalt and other magnet families may be evaluated when the operating envelope, corrosion environment, mechanical constraints, and cost structure support them, but they require a separate performance and supply assessment.
For motor designers, the economic question is broader than the Dy price per kilogram. Motor makers can reduce exposure through redesign, reduced heavy-rare-earth content, process control, and sourcing strategies, as covered in How Motor Makers Manage Magnet Price Spikes. A nominally lower-cost magnet that loses coercivity under rotor stress is not a lower-cost motor.
Specify by Composition, Grade, and Test Conditions
A purchase specification should state the magnet grade, minimum HcJ at 20 °C, recommended maximum operating temperature, residual induction Br, energy product, Dy content or permitted process route, coating, and dimensional tolerances [S1]. It should also identify whether the quoted composition applies to the bulk alloy or to a grain-boundary-diffused magnet, because the manufacturing route changes how the Dy is used [S2].
Three data points should remain visible in the datasheet: Dy concentration in weight percent, HcJ in kA/m, and maximum operating temperature in °C. For example, an SH material with minimum HcJ of 20,000 Oe, or 1,590 kA/m, can carry a typical Dy addition of 4–5% when processed through conventional alloying, although specific products and production methods differ [S1].
Materials testing remains essential because NdFeB magnets are manufactured as either sintered or bonded products [S4]. Sintered grades can contain heavy rare earth additions or receive grain-boundary diffusion, while bonded NdFeB uses a different powder-and-resin manufacturing route [S2][S4]. The label “high-temperature NdFeB” is not an adequate purchasing specification by itself.