HRE-Free UH Magnets: How Far Can the Technology Be Pushed?

Why Are HRE-Free UH Magnets Receiving More Attention?

HRE-free Neodymium magnets are not a new concept. For many years, however, completely eliminating heavy rare earths was not always necessary. The industry increasingly favored HRE-less magnets, using limited amounts of Dysprosium (Dy) or Terbium (Tb) when additional coercivity was needed. This approach became even more attractive as grain boundary diffusion (GBD) technology matured, allowing heavy rare earths to be used much more efficiently than in conventional bulk alloying.

This is why HRE-free UH magnets are receiving particular attention. UH-level coercivity has long been difficult to achieve without heavy rare earths, but the incentive to overcome that limitation is now much stronger.

The goal is no longer simply to demonstrate higher coercivity without Dy or Tb, but to achieve commercially useful UH grades while preserving the remanence, thermal stability, and manufacturing consistency expected from high-performance Neodymium magnets.

The development of HRE-free magnets is not simply a race toward higher coercivity. In practice, the performance boundary is being pushed in two directions: achieving higher remanence and energy product at an established coercivity level, and achieving higher coercivity while preserving as much remanence as possible.

The first direction is already important for HRE-free SH magnets. Once SH-level coercivity can be achieved without Dy or Tb, further development can focus on increasing remanence and maximum energy product without losing the required coercivity margin. This allows HRE-free materials to serve applications that demand both strong magnetic output and sufficient resistance to demagnetization.

The second direction is more obvious but also more difficult: extending HRE-free materials into higher-coercivity grades. HRE-free UH magnets are a key target because they require another substantial increase in coercivity while still maintaining commercially useful remanence and energy density. Simply producing magnets with higher intrinsic coercivity values is not enough if those gains come with excessive losses in remanence or overall practical performance.

These two directions are closely connected. Further increases in coercivity often require stronger grain-boundary isolation, more aggressive composition adjustment, or other measures that can begin to reduce remanence. At the same time, designs optimized for higher remanence and energy product leave less room for changes that favor coercivity. The challenge is therefore to expand the usable combination of coercivity and remanence rather than improve either property at the expense of the other.

At present, even HRE-free magnets at the lower-remanence end of the performance range still only approach the intrinsic coercivity required for standard UH grades. This suggests that the remaining gap toward commercially competitive HRE-free UH magnets is not simply a matter of obtaining a little more coercivity. Higher coercivity still needs to be combined with the remanence, thermal stability, and consistency expected from a standard commercial grade.

This does not mean that such materials have no practical value today. For applications with sufficient magnetic design margin, lower-remanence HRE-free options may still be worth evaluating, particularly where reducing dependence on Dy or Tb is important. Their suitability, however, should be assessed against the actual operating temperature, magnetic circuit, and demagnetization margin rather than the nominal grade alone.

The technologies being used to close this gap are not fundamentally new. They are further refinements of approaches already used in HRE-free magnets, including grain refinement, grain-boundary optimization, and composition adjustment. Their continued development can still improve coercivity, but the remaining gains are becoming increasingly difficult to extract.

Further grain refinement and better-controlled grain boundaries can suppress reverse-domain formation and reduce magnetic coupling between neighboring grains. Composition optimization can also provide additional gains. For example, increasing the proportion of Pr relative to Nd can raise the magnetocrystalline anisotropy of the main phase, while minor alloying elements can further modify grain-boundary phases. These approaches have already contributed to existing HRE-free grades rather than representing entirely new solutions for UH magnets.

This is why the path toward HRE-free UH magnets appears increasingly constrained. The same technologies that successfully expanded HRE-free performance into lower coercivity ranges can still be refined, but their remaining performance margin is limited. Reaching the UH coercivity level is difficult enough; doing so while also maintaining commercially competitive remanence, reliable thermal performance, and stable mass production is a much more demanding target.

Approaching the intrinsic coercivity of a conventional UH grade does not automatically make an HRE-free material an equivalent replacement. For HRE-free UH magnets, room-temperature Hcj is only one part of the requirement. The material must also provide sufficient remanence and retain adequate coercivity as operating temperatures rise.

Thermal and aging performance are particularly important. A material may show an encouraging intrinsic coercivity value at room temperature but still provide insufficient demagnetization margin at elevated temperatures or develop unacceptable irreversible magnetic losses after prolonged heat exposure.

Commercial grades also require a repeatable manufacturing window. HRE-free UH magnets must combine UH-level coercivity with useful remanence, reliable thermal stability, and consistent performance across production batches, magnet sizes, and geometries—not just in selected samples.

There is still room for HRE-free technology to improve, but the remaining potential should not be overstated. The key question is whether existing approaches can be pushed far enough to produce commercially useful HRE-free UH magnets while retaining the remanence, thermal stability, and production consistency expected from standard UH grades. UH is no longer completely out of reach, but it also appears to be approaching the practical limits of current HRE-free technologies.

UH remains more achievable at the lower-remanence end of the grade range. As higher remanence is required, the available room for further coercivity improvement becomes increasingly limited. This makes higher-remanence UH grades considerably more difficult, because coercivity, remanence, thermal stability, and manufacturing consistency must all be maintained at the same time.

Beyond UH, the outlook is much less clear. With currently available HRE-free approaches, EH and AH grades do not appear to be realistic near-term targets for the complete elimination of Dy and Tb. Heavy rare earths still provide valuable coercivity and high-temperature demagnetization margins in these more demanding performance ranges.

The likely future of HRE-free UH magnets is therefore gradual expansion rather than a sudden replacement of all HRE-containing grades. As materials and processes continue to improve, some applications that currently rely on Dy or Tb may move into the HRE-free range. Heavy rare earths will remain important, but the performance level at which they become necessary may continue to move higher.