Preference of the quadrupolar ordering in CeB6

We address the question as to why the ordering of O-xy-type quadrupole mome nt predominates that of T-xyz octupole moment at no applied field in CeB6,i n spite of the same coupling constant predicted. In the mean field approxim ation (MFA), the same results are obtained for the quadrupolar and the octu polar interactions. If we go beyond the MFA to apply the constant coupling approximation, it is shown that the ordering of O-xy is stabilized compared with that of T-xyz, as far as each interaction is treated separately.