Temperature dependent intensity in the optical absorption spectrum of ferromagnetic K2CrCl4

Abstract
Using the spin-wave spectrum of a two-dimensional ferromagnet with spins lying in the basal plane, the variation in the intensity of exciton-magnon combination bands in the visible absorption spectrum of the ionic ferromagnet K2CrCl4 (Tc approximately 65K) is quantitatively explained. The near-neighbour exchange integral of 3.5 cm-1 taken from the series-expansion fit to the high-temperature susceptibility of Gregson et al. (1975) gives a good fit to the intensity of the 15900 cm-1 band from 4 to about 15K.