Magnetic properties and microstructural characterisation of isotropic nanocrystalline Fe-Nd-B based alloys

The effects of a nanocrystalline structure on the magnetic properties of isotropic melt spun Fe-Nd-B alloy ribbon are discussed. Three classes of alloys are considered: (a) low Nd (8-10 at.%) which also contains alpha -Fe; (b) near-stoichiometric Nd contents (11-13 at.%) which are single phase Fe/sub 14/Nd/sub 2/B; (c) high Nd (16-20 at.%) which also contains a Nd-rich phase. For types (a) and (b), as the scale of the nanostructive decreases, the remanence J/sub r/ is increasingly above J/sub s//2, while the coercivity H/sub cj/ is decreased, with a linear J/sub r/-H/sub cj/ relationship. No J/sub r/ enhancement occurs for type (c) alloys, even for a nanocrystalline structure, but rather a decrease due to volume dilution of the Fe/sub 14/Nd/sub 2/B phase. These effects are discussed in terms of inter-grain exchange coupling and decoupling, and the implications with respect to permanent magnets with improved properties are considered. It is demonstrated that the benefits of enhanced J/sub r/ in terms of improved energy product are limited by corresponding attenuation of the coercivity.>