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 J4f-5d, J4f-6s and J4f-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-6p interactions, as expected from the Campbell model for the exchange interactions occurring in rare-earth-transition-metal intermetallics.