Acoustic birefringence at electromagnetic excitation of sound in iron borate crystals

High temperature antiferromagnets such as iron borate, hematite etc., have high magnetoelastic coupling. As a result, in the conditions of birefringence effect, there is a possibility to control parameters of sound waves by a small external magnetic field. On the other hand, high magnetoelastic coupling raises the sensitivity of sample magnetic system to external mechanical influences, for example from the side of acoustic contacts with piezotransdusers. In this paper the effect of contactless (electromagnetic) sound generation in external magnetic field, while minimizing the impact of external mechanical stresses on the magnetic properties of the sample is experimentally studied. As a result, the birefringence effect at the electromagnetic excitation of high-frequency ultrasonic wave is detected, which is of interest from the viewpoint of its instrument application. Comparison of a theory of birefringence effect with experimental data is conducted. The magnitude of a magnetoelastic gap for iron borate is obtained.