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

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Abstract
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 nRT between rare-earth and transition-metal ions and nRR 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 nRT 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.