Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

We present the results of studies on the temperature dependence of the electrogyration (EG) effect, Faraday rotation and natural optical activity in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals at the phase transition. A high EG coefficient is found for Pb5Ge3O11:Cr crystals. We demonstrate how the Curie–Weiss constant, the critical exponents of the order parameter and the dielectric permittivity in Pb5Ge3O11:Cr crystals, as well as the coefficients of thermodynamic potential, could be derived from the temperature dependences of optical activity and the EG coefficient. We also show that the increment of the Faraday rotation in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals appearing at the phase transition is caused by a combined magneto-electrooptic effect induced by spontaneous polarization. It is proportional to the square of spontaneous polarization. The phenomenon revealed by us corresponds to combined effects of crystal optics, which appear due to the common action of different fields.

Source:IOPscience

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