MAGNETIC-FIELD EFFECTS ON QUADRUPOLAR ORDERING IN A GAMMA(8)-QUARTET SYSTEM CEB6

A theory of the antiferro-quadrupolar ordering in CeB6 is developed in the framework of the Gamma(8)-quartet basis. Possible ordered phases under the external magnetic field are classified in terms of their sym metry properties, and the relations between quadrupolar order paramete rs and field-induced moments are established. Then we formulate a mean -field theory of Ohkawa's RKKY model based on the group-theoretical co nsideration. The stability of the possible phases and the resulting ph ase diagrams are analyzed in connection with the character of quadrupo lar moments, the influence of induced moments and the form of Zeeman t erm. Considering available experimental results, we introduce an impro ved model with asymmetric interactions and discuss the phase diagram o f CeB6. The connection between magnetostriction and uniform quadrupola r moments is discussed.