Villari effect in FeSe_1–xS_x

Acoustoelectric transformation (occurrence of electromagnetic radiation under the action of an elastic wave) in a FeSe_0.925S_0.075 crystal in the presence of an external magnetic field has been studied. It is shown that the application of the magnetic field along the direction of propagation of the elastic wave leads to a rotation of the plane of polarization of the emitted electromagnetic wave. The physical mechanism is that the elastic deformation leads to the appearance of a non-diagonal component of the magnetic susceptibility and to the generation of an additional alternating magnetic moment perpendicular to the external magnetic field and to the elastic displacement. The observed features are interpreted as a manifestation of the Villari effect. A phenomenological description of the experimental results is presented. The observed effect shows that the symmetry of the low-temperature FeSe_1–xS_x phase belongs to the triclinic syngony.