Grain boundary phenomena in NdFeB-based hard magnetic alloys

The NdFeB-based alloys were invented in 1980-ies and remain the best known hard magnetic alloys with highest magnetic energy product. The unique properties of NdFeB-based alloys are due to the thin layers of a magnetically isolating Nd-rich phase in grain boundaries (GB) and triple junctions (TJs). The prewetting (or premelting) phase transitions were the first reasons permitted to explain their existence. The deficit of the wetting phase in case of complete wetting can also lead to the formation of thin GB and TJ phases. However, only the phenomenon of pseudopartial (or pseudoincomplete, or constrained complete) wetting permitted to explain, how the thin GB film can exist in the equilibrium with GB lenses of a second phase with non-zero contact angle. The focused usage of such thin magnetically isolating GB layers can further improve the properties of NdFeB-based hard magnetic alloys.