Gakel’–Turov oscillations in iron borate

Abstract Dependence of the amplitude of transverse sound passed through a basal plate of easy-plane weak ferromagnet FeBO 3 on a magnetic field H , parallel to the plate is investigated in experiment at T =77 K. This dependence is of the oscillating form. The phenomenon is caused by magnetic birefringence of transverse sound, being the analog of Cotton–Mouton optical effect. In acoustics this effect is associated with magnetic additions appearing in elastic modules upon transition from a paramagnetic phase to an antiferromagnetic one. However, the theory of magnetoacoustic birefringence for homogeneously magnetized crystals, valid for MnCO 3 , is unable to explain the experiment for FeBO 3 . A model, taking into account the experimental boundary conditions and inhomogeneous distribution of magnetization in the sample of iron borate is constructed. Calculations based on this model describe the experiment satisfactorily.