Optical study of antiferromagnetic single crys in high magnetic fields

Infrared measurements and linear-spin-wave calculations for single-crystal (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) (x=0.0, 0.4, 1.0) in magnetic fields up to 30 T show that absorption features which have been ascribed to magnon excitations are very insensitive to the applied field. The substitution of (Formula presented) for (Formula presented) leads to an additional absorption feature, which does have a strong field dependence. This excitation is assigned to an intermultiplet transition in the (Formula presented) ion. The zero-field temperature dependence of this absorption shows clear evidence of an interaction between Cu and Pr spins.