Our latest work addresses a practical limitation of grain boundary diffusion (GBDP) in Nd–Fe–B magnets. When magnet thickness goes beyond about 4–5 mm, diffusion depth becomes too limited and the performance normally associated with thin magnets starts to deteriorate. In this study we show that a segmented architecture can avoid this problem. By stacking thin segments, thicker magnets can be built while still reaching the performance level of thin ones.

The segments are bonded using an ultrathin (~10 μm) low-melting Tb–Pr–Al–Cu–Ga alloy. This layer holds the pieces together while simultaneously acting as the diffusion source. Instead of hardening only the surface layer, the segmented structure spreads the effect through the whole magnet, which makes the Tb significantly more efficient. With only 0.16 wt.% Tb, coercivity rises from 1102 kA/m to 1748 kA/m, while remanence drops by only about 2% (from 1.44 T to 1.41 T).

Since thickness is no longer the limiting factor, the same approach also makes it easier to integrate Ce-containing segments. This enables hybrid magnet designs that rely less on critical heavy rare earth elements without compromising the overall magnetic performance.

The work was carried out in collaboration between TU Darmstadt and Fraunhofer IWKS.

A. Durgun, I. Dirba, K. Opelt, C.-C. Lin, J. Gassmann, O. Gutfleisch
Scripta Materialia 275 (2026) 117164.
DOI: 10.1016/j.scriptamat.2025.117164