Optical absorption intensity and short-range spin correlation in the ionic ferromagnets A2CrCl4(A=Rb, CH3NH3, CH3CH2NH3)

Abstract
The temperature variation of the intensity of an exciton-magnon combination band at 530 nm in the title compounds is related to the short-range spin correlation function calculated by the theory of Villain (1974), rather than the infinite-range spin correlation estimated from neutron diffraction and magnetisation measurements.