O. Suzuki

Quadrupolar ordering of Ce3Pd20Ge6

Abstract We present ultrasonic measurement of the ternary intermetallic compound Ce3Pd20Ge6, where quadrupolar ordering at TQ≈1.2xa0K occurs at a higher temperature than the antiferromagnetic ordering at TN=0.75xa0K. The Curie term in the quadrupolar susceptibility for the crystal-field ground-state Γ8 gives rise to a softening of the transverse modes (C11−C12)/2 and C44 above TQ. The most pronounced softening of 50% is observed for (C11−C12)/2 which suggests a ferroquadrupolar ordering of O02 or of O22 with Γ3 symmetry below TQ.

Magnetic phase diagram and low-temperature properties of Ce0.5La0.5B6

Abstract We have measured the low-temperature specific heat of Ce0.5La0.5B6 under the fields of H ||[1 1 0] . The present results support the non-magnetic ground state of Ce0.5La0.5B6. We confirm the absence of the phase III of Ce0.5La0.5B6 for H ||[1 1 0] .

Quadrupolar effect of R3Pd20Ge6 (R=Ce, Pr, Nd)

Abstract We have investigated the quadrupolar effects on ternary intermetallic rare-earth (R) compounds R3Pd20Ge6 by an ultrasonic method. Down to 0.4xa0K, the transverse modes (C11–C12)/2 and C44 of Pr3Pd20Ge6 exhibit pronounced softenings of 15.8% and 13.8%, respectively. In Nd3Pd20Ge6, the longitudinal C11 and the transverse (C11–C12)/2 modes exhibit softenings. These softenings of the elastic constants are described in terms of quadrupolar susceptibility for the ground states Γ3 of Pr3Pd20Ge6 and Γ8 of Nd3Pd20Ge6 with orbital degeneracy.

Low-temperature specific heat of CexLa1−xB6

We have measured low-temperature specific heat of CexLa1−xB6. No indication of long-range ordering was found in the specific heat of CexLa1−xB6 (x=0.6 and 0.5) within the limits of the accuracy of the measurements. On the other hand, a clear indication of long-range ordering (phase IV) was found in the case of Ce0.65La0.35B6. The ground state of CexLa1−xB6 in the low-temperature and low-field region would change from phase IV to a non-magnetic state at the critical Ce-concentration 0.6<xc<0.65 as a result of the competition between the intersite interactions and the dense Kondo effect.

Ultrasonic study of Kondo compounds CexLa1−xB6 (0.60⩽x⩽0.75)

Abstract We have performed the ultrasonic measurements to examine systematic change of the magnetic-phase diagrams of the Kondo compound CexLa1−xB6 with the Γ8 ground state as a function of cerium concentration x. A long-range ordered phase IV is observed in addition to an antiferroquadrupolar phase II and an antiferromagnetic phase III in the compounds of x=0.75, 0.70 and 0.65. The huge softenings of C44 in phase IV indicate considerable enhancement of the quadrupolar fluctuation with Γ5 symmetry. With decreasing cerium concentration x, the ground state of CexLa1−xB6 at low temperatures under low-magnetic fields changes from the ordered phase IV to a non-magnetic state due to the Kondo effect in vicinity of x∼0.60.

Low-temperature specific heat of Ce0.5La0.5B6☆

Abstract We have measured low-temperature specific heat of Ce0.5La0.5B6. The specific heat for H = 0 shows a broad peak around TK. No indication of long-range ordering is observed for H = 0. Under magnetic field, anomalies of the specific heat associated with transitions into the antiferromagnetic or antiferroquadrupolar phase are observed.