Multipole ordering in f electron systems

We discuss multipole ordering in two cubic f-electron compounds. Field variation of the antiferroquadrupolar transition temperature T_Q in PrPb₃ is determined by the specific heat and the magnetization measurements. It is found that T_Q(H) shows a pronounced increase for H ∥ 〈 100 〉, which has been successfully explained by the antiferromagnetic interaction between the field-induced staggered moment in the O₂⁰(∝ 2J_z² - J_x² - J_y² AFQ phase. From the analysis of the anisotropy in T_Q(H), the importance of an octupolar interaction is pointed out. The new ordered state in Ce_xLa_1-xB₆ (x < 0.8), called phase IV, has been examined by magnetization measurements under uniaxial pressures. A pronounced anisotropy is observed at a relatively weak pressure, and the ordering temperature seems to increase in magnetic field. The results are discussed in view of a possible octupolar ordering in phase IV.