Effects of screening on crystal-field magnetoelastic coupling in rare-earth intermetallic compounds

The effect of screening by conduction electrons on the magnetoelastic coupling due to the crystal field in the Laves-phase rare-earth (RE) intermetallics is calculated and applied to REAl 2 compounds. The Thomas-Fermi and Hartree approximations for the screening are considered. Tetragonal, orthorhombic and rhombohedral strains are considered through the distortion of the lattice and of the screening and ligand-ion charge densities. The effect of the screening on magnetoelastic parameters is substantial. The introduction of conduction band exchange is able to modify the sign of the tetragonal parameter compared with the bare-ion point-charge model. The Friedel oscillations of the crystal potential modify the sign of the rhombohedral mode as well. A comparison with available magnetoelastic data for the compounds NdAl 2 , PrAl 2 and TbAl 2 is presented and good agreement with calculations is obtained if conduction electron band exchange is envisaged.