Hydrogenation of the high-coercivity Nd-Fe-Al amorphous alloy

In this paper we have looked at the effects of a range of hydrogen pressures and temperatures on the magnetic and structural changes in Nd-Fe-Al alloys with compositions close to Nd60Fe30Al10, using vibrating-sample magnetometry, X-ray diffraction and transmission electron microscopy. Our results suggest that the material is resistant to hydrogen at low pressures and temperatures, but at approximately 30 bars and 100 degrees C the material absorbs about 0.60 +/- 0.05 weight% of hydrogen. After this hydrogen absorption the coercive field decreases significantly, i.e., from 3750 Oe before to 120 Oe after the hydrogenation. We have considered the strong-domain-wall-pinning model to explain the coercive field and its drop as a result of the hydrogen absorption. This model can be used to describe the material in the temperature range 250-450 K before hydrogenation for a domain-wall width of 7 nm. After hydrogenation the material displays soft-magnetic behaviour and the possible origins of this are discussed. Our results have demonstrated the important role that hydrogen can play in modifying the structure and properties of rare-earth-transition-metal-based permanent-magnet materials. (C) 2012 Elsevier Ltd. All rights reserved.