Magnetic Phase Diagrams of Kondo Compounds Ce_<b>0.75</b>La_<b>0.25</b>B_<b>6</b>and Ce_<b>0.6</b>La_<b>0.4</b>B_<b>6</b>

Abstract

We measured the elastic and thermal properties to examine the competing effect between the intersite interactions and the Kondo coupling in Ce 0.75 La 0.25 B 6 and Ce 0.6 La 0.4 B 6 with the Γ 8 ground state. The huge softening of the transverse C 44 mode of both compounds at low temperatures indicates a remarkable fluctuation of the quadrupolar moments O y z , O z x and O x y with Γ 5 symmetry. In the magnetic phase diagram of Ce 0.75 La 0.25 B 6 , we found a new ordered phase IV in addition to the antiferroquadrupolar phase II and the antiferromagnetic phase III. The compound Ce 0.6 La 0.4 B 6 , however, shows the Fermi liquid state without the long-range order at low fields and transits into the ordered phase II or III in the magnetic field above 16 kOe.