Gyrotropic properties and birefringence of Smx Tb1−xFeO3 in spin reorientation range

The polar diagrams of the Sm_xTb_1−xFeO₃ system taken for the crystallographic directions [110] and [001] have been investigated. The gyrotropic measurements data are compared to the values of the bond angles θ₁ and θ₂ calculated in terms of the lattice parameters. The correlation between the crystallographic and optical properties change as a function of composition has been obtained for the system under investigation. -The temperature measurements of the gyrotropic properties of SmFeO₃ and Sm_0.8Tb_0.2FeO₃ have shown that with temperature rising a change of shape and character of the polar diagrams takes place. The birefringence temperature dependence for Sm_0.8Tb_0.2FeO₃ in the transparency and absorption range has been determined. The results of the study show the existence of the interrelation between the crystallographic, optical and magnetic characteristics and indicate that the temperature range of spin reorientation can be reliably determined from the optical measurements.