Far infrared spectra of magnetic ions in crystals

Abstract

The absorption spectra of magnetic ions in crystalline solids, observed in the spectral range between approximately 5 and 200 cm−1, are surveyed. The electronic excitations of single ions are considered first. The measurements of line positions, intensities and widths are discussed in terms of both static and dynamic crystal electric field models. The second half of the review deals with the excitation of coupled ions both in dilute and concentrated materials. The spectra observed are discussed in terms of current models of the various interactions which can occur. In both areas there are obvious gaps between the experimental data and their theoretical interpretation. For pairs of interacting ions the theory is well advanced but as yet there is little data available for interpretation; while for many effects in single ion spectra the difficulties inherent in the theory limit our understanding. Progress towards the elimination of these problems is likely to aid our understanding of the behaviour of ions in crystals.