ROTATION-INVARIANT THEORY OF ACOUSTIC BIREFRINGENCE IN A FERROMAGNET

The acoustic birefringence effect in a cubic ferromagnetic crystal is investigated on the basis of a rotation-invariant theory. It is shown that the inclusion of rotation-invariant terms in the thermodynamic po tential density creates an additional term in the phase shift for acou stic birefringence associated with different renormalizations of the u ltrasonic wave velocities. It is also shown that the occurrence of aco ustic birefringence in crystals with weak magnetostriction can be attr ibuted to magnetic crystallographic anisotropy.