Multipolar excitations in the antiferroquadrupolar phase of CeB6

The hexaboride compound CeB6 exhibits quadrupolar O-xy type and magnetic order due to the four-fold degenerate Ce3+-Gamma(8) CEF-states. The B-T phase diagram shows anomalous large positive slope of the critical field curve. This is due to a new type of induced octupolar T-xyz order parameter. Inelastic neutron scattering experiments by Bouvet have provided direct evidence for the existence of collective excitations. Their nature is shown to be of mixed multipolar character and their dispersion and intensities are calculated using a RPA-type approach and a Holstein-Primakoff approach which show excellent agreement. Temperature and field dependence of the multipolar excitations are calculated and the latter is compared to experimental results. (C) 2004 Elsevier B. V. All rights reserved.