Magnetic phase diagrams of CexLa1-xB6 in high magnetic fields

We have performed ultrasonic measurements under high magnetic fields up to 30T by using the hybrid magnet at the National Institute for Materials Science to investigate the magnetic phase diagram for antiferroquadrupole (AFQ) phase II in CexLa1-xB6. With increasing Ce concentration x from x=0.50, the AFQ phase transition temperatures TQ indicate an almost linear increase in various fields. The large magnetic anisotropy of AFQ phase II, in which TQHparallel[001] is much smaller than TQHparallel[110] and TQHparallel[111] in high magnetic fields, is revealed in x=0.75,0.60 as well as in x=0.50. These experimental results support the theoretical calculation based on the Γ5-type AFQ ordering and the magnetic field induced octupole Txyz