Effect of external factors on the exciton line in the optical spectrum of the cubic antiferromagnet RbMnF3

Abstract

The magnetic dipolar line splitting of the pure exciton6A1g→4Eg(4G) transition has been investigated experimentally in a wide range of magnetic fields (reaching 300 kOe) and with the application of uniaxial stress along the basic crystallographic directions. In the general case the observed splitting is produced by two mechanisms. The reorientation of the sublattice magnetic moments brings about a removal of the twofold orbital degeneracy of the4Eg(4G) state. The violation of the moments' strict collinearity results in the Davydov splitting. A magnetoelastic mechanism of the degeneracy lift has been given a detailed consideration. On the basis of the spectroscopic data numerical estimates are obtained of the magnetoelastic constants. The alteration of the exchange fieldHE for theU2+ transition to the excited state4Eg(4G) has been evaluated from the “mass-center” shift of the Davydov doublets that takes place in high magnetic fields. The intensities and polarizations are calculated in the Heitler—London approximation of the exciton transition Davydov components. The orbital portions of the wave functions of the involved states are simple cubic harmonics. The Davydov split zones have been identified and the sign determined of the intersublattice resonant interaction energy.