Exciton Absorption Lines during Spin Reorientation in Antiferromagnetic YCrO3

Abstract

Spectral changes of the exciton absorption lines in YCrO 3 observed during the field-induced spin reorientation are studied on the basis of the method of an effective Hamiltonian. The effective Hamiltonian expanded in powers of a magnetic field is made invariant to the symmetry operations of the magnetic group to which the spin arrangement during the spin reorientation belongs. The values of the parameters in the effective Hamiltonian are determined so as to fit the observed line shifts. The relative intensities of the exciton lines calculated by using these values of parameters are in a good agreement with experiments. By expressing the absolute values of the energy-transfer matrix elements in various Cr 3+ -pairs in terms of these parameters, the magnetic-field dependences of these matrix elements are obtained and their physical implication is discussed.