New mechanism of electric-dipole absorption of light in antiferromagnets

A study is made of the absorption of light in antiferromagnetic crystals containing 3 d ions displaced from a center of symmetry. Experiments revealed that the inducing of noncollinearity of the magnetic structure by a strong external magnetic field is accompanied by a marked intensification of the purely excitonic bands of absorption of light. On the basis of this observation a new mechanism of electric-dipole absorption of light is proposed wherein a dipole moment is induced in a pair of magnetic ions coupled by exchange interaction, as a result of which an exciton is excited on one ion. The enhancement of the absorption of the exciton bands that follows from the proposed mechanism is in agreement with experimental data.

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