Abstract
We address the question as to how the coexistence and the fluctuation of the interactions affect the properties of phase I and II in CeB6. For that purpose, we develop the theory of the constant coupling approximation for the coexistent system of the interaction of Oxy-type quadrupole moments and that of Txyz octupole moment, including the Zeeman effect. It is shown that the increase of the transition temperature between phase I and II with increasing applied magnetic field is caused mainly by the cooperation of the Oxy and the Txyz interactions. The pronounced features of the specific heat and the magnetization are reproduced, because both the effects of coexistence and fluctuation of the interactions are taken into account in the present calculation.
