Solid-solution stability and preferential site-occupancy in (R-R′)₂Fe₁₄B compounds Available to Purchase

The rare-earth (R) uniaxial anisotropy of R₂Fe₁₄B compounds with magnetic R atoms (e.g., Nd or Pr) is at the origin of the exceptional hard magnetic properties achieved in magnets based on these compounds. The uniaxial anisotropy found in Ce₂Fe₁₄B is attributed mainly to the magnetism of Fe. Ce is the most abundant R element and there has been much recent effort to fabricate magnets in which Ce is partially substituted for Nd. In the present neutron study of (R_1−xCe_x)₂Fe₁₄B (R = La or Nd), Ce is found to enter the R₂Fe₁₄B phase over the entire composition range. The crystallographic parameters decrease with increasing Ce content and the Ce atoms preferentially occupy the smaller 4f sites. It is concluded that Ce in these (RR′)₂Fe₁₄B compounds essentially maintains the intermediate valence character found in Ce₂Fe₁₄B. It is proposed that, in this intermediate valence state, Ce weakly contributes to uniaxial anisotropy, thus making a link with the fact that significant coercivity is preserved in Ce-substituted NdFeB magnets.