Antiferromagnetic conical refraction of elastic waves in hematite

Conical refraction, which is due to the renormalization of the elastic moduli by the effective magnetoelastic interaction and depends on the static magnetic field, has been experimentally observed in an α-Fe₂O₃ trigonal easy-plane antiferromagnet in addition to the usual internal conical refraction of transverse elastic waves propagating along the trigonal C ₃ axis. It has been shown that the deviation angle θ_η of the energy flux from the C ₃ axis at the internal conical refraction is independent of the magnetic field applied in the basal plane (H ⊥ C ₃) and is a constant determined by the ratio of the elastic moduli C ₁₄ and C ₄₄. The deviation angle of the energy flux at the antiferromagnetic conical refraction increases with the magnetic field and approaches the value θ_η at large H values. The results are well described by the theory of this phenomenon developed by E.A. Turov and confirm its basic conclusions.