MAGNETIC-PROPERTIES AND MICROSTRUCTURAL CHARACTERIZATION OF ISOTROPICNANOCRYSTALLINE 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 class es of alloys are considered: a) low Nd (8-10 at.%) which also contain alpha-Fe; b) near-stoichiometric Nd contents (11-13 at.%) which are si ngle phase Fe14Nd2B; c) high Nd (16-20 at.%) which also contain a Nd-r ich phase For types a) and b), as the scale of the nanostructure decre ases, the remanence J(r) is increasingly above J(s)/2 while the coerci vity H(cj) is decreased, with a linear J(r)-H(cj) relationship. No J(r ) enhancement occurs for type c) alloys, even for a nanocrystalline st ructure, but rather a decrease due to volume dilution of the Fe14Nd2B phase. These effects are discussed in terms of inter-grain exchange co upling and de-coupling and the implications with respect to permanent magnets with improved properties are considered. In particular, it is demonstrated that the benefits of enhanced J(r) in terms of improved e nergy product are limited by corresponding attenuation of the coercivi ty.