Direct observation of a manifestation of magnetoelastic coupling in a low-dimensional virtual ferroelastic

The propagation velocities of acoustical vibrations are measured for differ ent directions of propagation and polarizations in layered alkali molybdate s at low temperatures. A comparison is made of the experimentally obtained absolute sound velocities in virtual ferroelastics and in systems with the cooperative Jahn-Teller effect. The temperature dependence of the sound vel ocities are investigated experimentally in these systems. The change in the sound velocities in an external magnetic field gives the first direct proo f of the presence of an interaction between the magnetic and elastic subsys tems of a virtual ferroelastic. A comparison with the theoretical calculati ons suggests the presence of a nonlinear coupling of the electronic subsyst em with optical phonons. (C) 2000 American Institute of Physics. [S1063-777 X(00)00705-2].