R-T and R-R exchange interactions in the rare-earth (R)-transition-metal (T) intermetallics: an evaluation from relativistic atomic calculations

Intra-atomic exchange integrals J 4f-5d , J 4f-6s and J 4f-6p for rare-earth trivalent ions were obtained from relativistic self-consistent field atomic calculations, using the local-density approximation for exchange and correlation potential. The effective (molecular-field) exchange coefficients n RT between rare-earth and transition-metal ions and n RR between rare-earth ions were obtained based on a simplified three-sublattice (4f, 3d and conduction electron) mean-field model. Quantitative results show a decrease in magnitude of n RT across the rare-earth series, which agrees well with values observed in many rare-earth-transition-metal intermetallic series. It is shown that the 4f-5d exchange interaction is far more important than the 4f-6s and 4f-p interactions, as expected from the Campbell model for the exchange interactions occurring in rare-earth-transition-metal intermetallics.