Optical and magneto-optical study of the transparent ionic ferromagnet Rb2CrCl4

Abstract

The visible absorption spectrum of the transparent ionic ferromagnet Rb2CrCl4 has been recorded as a function of temperature from 0.85 to 50K and in magnetic fields up to 5T applied along (100), (110) and (001). Above 3K the intensities of all the bands vary approximately as T2, as predicted by Gregson et al. (1975, 1976) for a two-dimensional easy plane ferromagnet. Below 2K the 631 nm band is resolved into two components, one almost independent of temperature and the other having an intensity which increases with temperature as T2 exp(-E(0)/kT). They are assigned respectively as spin wave creation and annihilation sidebands with E(0), the zone-centre gap in the spin wave spectrum, 1.20+or-0.15K. All the bands lose intensity on applying a magnetic field, following the function T2 exp(-(E(0)+g mu BH)/kT), from which g-values are derived. The behaviour of the 631 nm band system agrees very well with the calculations of Elliott et al. (1980).