FERROMAGNETIC GRAIN-BOUNDARY SIGNATURE IN DIE-UPSET RE-FE-B MAGNETS

Previous nanostructural and nanocompositional studies performed on the boundaries of deformed grains in two die-upset rare earth magnets wit h bulk compositions Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6 indicate tha t the intergranular phase in many grain boundaries is enriched in iron relative to the bulk. We present here preliminary magnetic data that provide further evidence that this grain boundary phase is indeed iron -rich, and in fact appears to be ferromagnetic. Hysteresis loops were performed at 800 K on die-upset magnets with the above compositions. E ach sample showed a clear hysteresis with coercivities between 34 and 40 Oe and an average remanence 4 pi B-R of 6.8 G for the Nd-based samp le and 10.3 G for the Pr-based sample. The ferromagnetic signals measu red at high temperature in these magnets are attributed to the iron-ri ch grain boundary phase. The implications of this conclusion with resp ect to coercivity are discussed.