  The origin of non-collinear magnetism under quadrupolar ordering is
investigated with CeB6 taken as a target system. The mode-mixing effect among
15 multipoles is analyzed based on the Ginzburg-Landau free energy. Then the
lower magnetic transition temperature and the order parameters are derived
within the mean-field approximation. In the presence of pseudo-dipole-type
interactions for the next-nearest neighbors, the observed pattern of
non-collinear ordering is indeed stabilized for certain set of interaction
parameters. The stability of the phase III' in the magnetic field is also
explained, which points to the importance of the next-nearest-neighbor
octupole-octupole interaction. Concerning the phase IV in CexLa1-xB6 with x ~
0.75, a possibility of pure octupole ordering is discussed based on slight
modifications of the strength of interactions.
