CRYSTAL-FIELD PHENOMENA IN RARE-EARTH COMPOUNDS

The basic formalism describing the crystalline electric field (CEF) interaction in rare-earth compounds is presented as a perturbation of the spectroscopic state of a free ion in the form of the Stevens operator equivalents. We then emphasize the relation between the CEF effects and the inelastic neutron scattering technique which is a unique tool to study the CEF excitations, especially in optically opaque metallic systems. Using a single-ion approximation as a starting point, we discuss how the study of the CEF effects helps to understand fundamental interactions in different materials, including weak and hard magnets, intermediate valence compounds, and high temperature copper-oxide superconductors.