Raman-Nath acoustooptical diffraction in antiferromagnet α-Fe2O3 induced by modulation of the polarizations of optical normal modes

Abstract

Raman-Nath acoustooptical diffraction was experimentally revealed in easy-plane antiferromagnet α-Fe2O3. The diffraction is due to linear modulation of the polarizations of the optical normal modes propagating along trigonal axis C3 of the crystal due to oscillations of the antiferromagnetism vector L caused by magnetoelastic interaction. The dependence of the diffraction parameters on a dc magnetic field H⊥ applied in the basal plane was studied. The dependence obtained is in good agreement with the field dependence of the exchange enhancement coefficient of magnetoelastic coupling in fields higher than that at which hematite transforms to a single-domain state (HD ∼ 1.8 kOe). for a sound flux power of about 1 W/cm2 in a sample, the maximum intensity of the diffracted wave at H⊥ = HD is about 0.9% of the input light intensity and its polarization is perpendicular to that of the incoming linearly polarized wave. The results obtained agree qualitatively with the theory of acoustooptical diffraction in antiferromagnets and confirm the antiferromagnetic mechanism of diffraction in the experimental geometry under study.