Magnetic and structural characteristics of some 2:17 rare earth-cobalt systems

The R2Co17 systems occurring in the Th2Ni17 (hexagonal) structure have six magnetic sublattices - R in the 2b and 2d sites and Co in the 6g, 12j, 12k and 4f sites. The overall magnetic behavior is the result of a complex interplay between the several magnetic sublattices. In Er2Co17 and Yb2Co17 only the 2b and 12j sublattices lead to the uniaxial anisotropy which is desired for permanent magnet fabrication. The useful magnetic properties of these systems can be enhanced by partially replacing the rare earth with Pr and Co by Fe and/or Mn. Fe-containing systems are particularly interesting because they have large magnetizations, high Curie temperatures and relatively strong magnetic anisotropies. Inclusion of Pr in place of Er or Yb produces a substantial increase in magnetization plus a modest increase in anisotropy. The rise in anisotropy is attributed to preferential replacement of Er or Yb by Pr in the 2d sites. In these sites, theory shows Er and Yb to have planar and Pr axial anisotropy, and it is for this reason that the incorporation of Pr in the lattice increases the uniaxial anisotropy. The increase in anisotropy when Co is replaced by Fe and/or Mn seems to arise in two ways - (1) preferential substitution at the dumbbell sites and (2) band structure effects. (orig.)