QUADRUPOLAR ORDERING AND LATTICE DEFORMATIONS IN RARE-EARTH COMPOUNDS

A model (J = 1) system of rare earth compounds is examined to discuss quadrupolar ordering and pertinent lattice deformations beyond the sta ndard approximation within MFA and RPA. In MFA the total set of quadru polar moments is examined; interrelation between them is shown to have physical and methodical signification. Inhomogeneous magnetoelastic i nteractions and finite phonon life-time are assumed within RPA and are shown to manifest themselves in quadrupolar excitations spectra throu gh phonon-mediated quadrupole-quadrupole interactions.