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 °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.

► Hydrogen absorption capacity of NdFeAl alloys comparable to other BMGs.
► After hydrogenation Nd nanoparticles transform to Nd2H5.
► High coercivity of starting material results from pinning of domains by Nd crystals.
► Nd–Fe–Al alloy changes from a hard magnet to a soft magnet after hydrogenation.