抄録
An octupole ordering model is studied by the mean field theory, and its relevance to the phase IV of CexLa1−xB6 is discussed. The observed lattice distortion along the [111] direction is interpreted in terms of the Γ5g-type ferro-quadrupole moment induced by an antiferro-octupole ordering with Γ5u symmetry. The octupole model also accounts for the cusp in the magnetization as in the Néel transition, and the softening of the elastic constant C44 below the ordering temperature. However, the internal magnetic field due to the octupole moment is smaller than the observed one by an order of magnitude. Also discussed is the possibility of a pressure induced antiferromagnetic moment in the octupole-ordered state.
